Kirkby calibration kit alternatives? - Page 1
Forum section: electronics / testgear

author: rfspezi
author_rank: Regular Contributor
timestamp: February 18, 2018, 10:25:21 am
content: I'm in search for an affordable VNA calibration kit (6 GHz, SMA female) for my 8753E.The Kirkbymicrowave kit seems to be a good choice - however price has risen from 380 to over 600 USD recently?That's why i hope somebody can recommend an alternative.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 18, 2018, 12:55:57 pm
content: you are not paying the device or the material. you are paying the calibration data and service support. without it, you better off with DIY kit. which i had and compared with Kirkby Cal Kit. i'm not aware of cheaper option that can provide custom calibration data just as Kirkby did, sorry. as he put it himself, it means like... "you may believe whatever you want to believe". so its either Kirkby or DIY, imho. ymmv.

author: Safar
author_rank: Regular Contributor
timestamp: February 18, 2018, 02:31:08 pm
content: Some sellers from China on ebay sell kits with PNA trademark.They wrote in description:"Accurate electrical models are needed of the opens and short circuits. A number of eBay sellers sell low-cost calibration kits, but these are effectively useless, as they don't have the mathematical models of the opens and shorts necessary to load the constants into a VNA, and we doubt they have optimal phase difference between open and short. This kit is different, in that it is designed, rather than just assembled. With this calibration kit, there is a support page with information on what coefficients to use for Agilent/HP,R/S,ADVANTEST,ANRITSU...".Price is just 218 USD for SMA kit and looks good generally BUT I'm don't know quality and have no any information about this kits and where to get this calibration data.I suppose that would be clever to ask him first for characterization equipment and what data they provide for each kit and look for some info if it possible.

author: Pitrsek
author_rank: Regular Contributor
timestamp: February 18, 2018, 03:25:35 pm
content: SDR kits is offering onehttps://www.sdr-kits.net/index.php?route=product/product&path=66_68_69&product_id=50Depending on your frequency range, transmission line based calibration might be a viable option.

author: hendorog
author_rank: Super Contributor
timestamp: February 19, 2018, 04:43:43 am
content: Quote from: Safar on February 18, 2018, 02:31:08 pmJudging by the pictures of the VNA they show in the auction, these are complete rubbish.

author: Tony_G
author_rank: Super Contributor
timestamp: February 19, 2018, 05:18:51 am
content: Quote from: hendorog on February 19, 2018, 04:43:43 amInteresting. That text is copied directly from Dr Kirkby's auction. I wouldn't trust a cal kit from someone willing to copy text like that.Full disclosure, i have 2 Kirkby kits and have been very haopy with them.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 19, 2018, 06:28:23 am
content: Quote from: hendorog on February 19, 2018, 04:43:43 amanything without calibration data are... including those heavily used brand name cal kit many sold in ebay, from accuracy stand point imho. i was to reply long post to the OP describing the pro to Kirkby cal kit, but since he's looking after cheaper option, i decided a short version of a reply. those china ebay just copy pasted Kirkby ads, less custom calibration data and less support service. and remember the china version only provides female or male version not both. Kirkby provides both gender, including throughs, a pen drive containing hand made calibration data with unique serial number to the cal kit and a -3dB verification attenuator, so we can compare the respond plot from calibrated HP8720D compared to our VNA so we know where our VNA stands. as soon we want to purchase a complete set from cheap china matching Kirkby's, the cost will be about the same if not slightly cheaper than. as i simply concluded in earlier post, anything without calibration data will be not much better or worse than a DIY kit. ymmv.

author: hendorog
author_rank: Super Contributor
timestamp: February 19, 2018, 06:41:12 am
content: Quote from: Mechatrommer on February 19, 2018, 06:28:23 amThat is not quite the full story. The cheap eBay kits clearly use poor components whereas the SDR kits use decent quality components. I'd expect that the SDR kits product will be quite a bit better than a DIY attempt.Here is another low cost option :- If you know someone who has a cal kit then you can purchase good quality parts and characterise them. There is a Matlab script which will work out the coefficients.

author: G0HZU
author_rank: Super Contributor
timestamp: February 19, 2018, 10:38:34 am
content: I think it's possible to make a cheap but decent DIY SMA cal kit for use up to maybe 3GHz. I did this many years ago and I still use this cal kit today for many applications. The short and load and open were all DIY using SMA end launchers and I worked out the correction factors myself for the user cal file.I get very good results with this cal kit and I typically use it to help me model SMD components up to a few GHz.Once above 3GHz I'd prefer to use a used but decent commercial cal kit, eg a healthy 3.5mm 85033E mechanical cal kit or a 3.5mm Ecal kit. I don't think I'd want to pay $600 for the Kirkby kit. Old/used commercial cal kits can suffer damage and wear so some caution would be needed but I'd still prefer to go down this route compared to a cheapo SMA based alternative no matter how much time and effort went into measuring the cal coefficients.

author: Safar
author_rank: Regular Contributor
timestamp: February 19, 2018, 05:31:50 pm
content: Quote from: Tony_G on February 19, 2018, 05:18:51 amIt is really interesting. I have not seen Kirkby description before. Agree.

author: hendorog
author_rank: Super Contributor
timestamp: February 19, 2018, 06:51:33 pm
content: Quote from: G0HZU on February 19, 2018, 10:38:34 amGood point, I had forgotten that you had done that. It is very well done and is light years ahead of the eBay offering.https://www.eevblog.com/forum/testgear/agilent-8753es-and-other-vnas-this-kind/msg1063141/#msg1063141In comparison, the cheap eBay kit is shown in the pictures at about 10dB return loss on the load at 3GHz. It looks to be only usable below 500MHz perhaps.Here is a useful page as well for DIY cal kits:http://www.qsl.net/in3otd/electronics/VNA_calkit/calkit.htmlQuoteThe issue with that is the availability of those used kits. They are very rare at reasonable prices, the sellers seem to think that even the boxes are worth a fortune.Overall, I think that the simplest approach is to purchase some quality parts, get them tested by someone with a real cal kit, and then determine the coefficients using the script in the link above.

author: G0HZU
author_rank: Super Contributor
timestamp: February 20, 2018, 10:22:20 pm
content: Thanks. I had a quick look over the Kirkby website and there are a few things that give me slight concern.QuoteIt would be nice to see some test setup info and some data on this. My first reaction is to run to the hills because this spec of 4 degrees doesn't sound good... maybe I'm misinterpreting what is meant here? .. or maybe it's a typo on the website and the spec is much better than this?Also, the kit appears to use regular SMA F-F bullets with the standard screwed at the end. It looks cheap... The closeup images of the short and open don't inspire me. I wouldn't expect a regular SMA bullet to qualify as being part of a VNA cal kit that runs to 7GHz. Maybe these are special versions of the SMA F-F. I'm used to the Suhner ones at work. Also, what happens if the cap rotates? Do you tighten it again with a torque wrench and hope the cal is still good? Maybe it works a lot better than it looks?An ex colleague of mine bought one of these kits recently and I could maybe try and borrow it and test it. At work, I've got access to new and UKAS calibrated PNA VNAs and various calibrated mechanical kits and several Ecal modules and some £££ Rosenberger test cables. I think the cables cost about £1500 each!

author: hendorog
author_rank: Super Contributor
timestamp: February 20, 2018, 10:30:04 pm
content: Quote from: G0HZU on February 20, 2018, 10:22:20 pmI vote hell yes!! Please do if you can swing it.

author: G0HZU
author_rank: Super Contributor
timestamp: February 20, 2018, 10:50:07 pm
content: Sadly, he's unlikely to lend it to me unless he goes on holiday because he uses it every day for his business. So it might take a while.You posted up a link to that (fringe) cal coefficient tool using GNU Octave but it looks like it is still being developed.For my homebrew cal kit here I embed keysight's polynomial for the fringe capacitance (for the OPEN) into an RF simulator and make all the coefficients variable. Then I use a simple tline model plus the polynomial result to predict the phase result of an ideal model. I then compare against the homebrew open after a mechanical or Ecal calibration. On the real homebrew standard I used a fine rotary tool to optimise the end of the open and I got very good agreement out to well beyond 3GHz. But I only made this kit for use with my first VNA and so it only had to be good to 3GHz. It's lasted many years and I still use it a lot. If I made another I'd expect to get better results for the short and open and maybe get it to work up at higher frequencies too. I'm not sure how valid my approach for the fringe capacitance was but it seemed to work OK on the simulator. Back then I would have measured and optimised my open and short at work on an old 6GHz HP8753ES with an 85033E cal kit.

author: orin
author_rank: Frequent Contributor
timestamp: February 21, 2018, 01:07:42 am
content: Quote from: G0HZU on February 20, 2018, 10:22:20 pmA fair proportion of that 4 degrees will be the uncertainties in measuring the actual phase of the standards. According to the datasheet, the 8720D's uncertainty is close to 2 degrees in the 2-8GHz range for a 1.0 reflection coefficient.QuoteIn the Kirkby SMA kit I have, the female standards do indeed use an F-F adapter (and the male standards seem to use an M-F adapter). The F-F adapters have flats so they can be held by a wrench when being connected, so you shouldn't be holding them by the cap. Given the variation in SMA connector design, I'd guess the results using the male open on its own with varying female SMA connectors were unacceptable. Adding the adapters ensures a consistent interface to the actual male open and must give better overall results or Dr Kirkby wouldn't have done it that way.

author: G0HZU
author_rank: Super Contributor
timestamp: February 21, 2018, 03:02:11 am
content: FWIW here's a phase comparison plot that may be of interest. This is a relative phase measurement of my homebrew OPEN.The two measurements were take many years apart and one was with an old HP8753ES with 85033 cal kit at work and the other is with my modern 13.5GHz Ecal module on a fairly modern ENA VNA. This was taken today.There is a difference and this could be wear and tear and it could be the torque. I used different torque tools.But the result looks sensible to me. The vertical blip in the data is a 0/360 degree wraparound in the simulator so ignore this.Next to this is an old plot of my simulation model of the 85033 OPEN that is based on the data in the cal kit as below. I used the delay and the C0, C1, C2 and C3 data in the model and ran it on the simulator. It is compared to an 8753ES doing a self measurement of its OPEN.60 ! OPEN: $ HP 85033 Open70 ! Z0 50.0 $ Ohms80 ! DELAY 29.243E-12 $ Sec90 ! LOSS 2.2E+9 $ Ohms/Sec100 ! C0 49.433E-15 $ Farads110 ! C1 -310.131E-27 $ Farads/Hz120 ! C2 23.168E-36 $ Farads/Hz^2130 ! C3 -0.16E-45 $ Farads/Hz^3When I was messing with my HP8714B many years ago I calibrated a company HP8753ES with an 85033 cal kit and then used it to remeasure its own OPEN standard. I then exported the data in an S1p file. If I compare the S1p file to the mathematical model for the C0, C1, C2 and C3 polynomial and the delay and compare relative phase I get the plot on the right below. It looks like a flat line.The VNA is measuring it's own cal kit 'OPEN' so it will display a response of a very tiny length of transmission line that has an open with some fringing capacitance at the end. It does agree with the model. Obviously, the VNA is measuring its own reference here so the result looks good but the point is the simulator model I created does seem to agree very closely.

author: G0HZU
author_rank: Super Contributor
timestamp: February 21, 2018, 09:00:36 pm
content: Quote from: orin on February 21, 2018, 01:07:42 amMy suspicion is that due to the fact that the kit uses regular SMA F-F bullets and screw on caps the SHORT will have stray inductance between the interface between the end of the SMA bullet and the metal face/pin in the end cap. There won't be a perfect interface here so there could be a tiny air gap that introduces inductance. This on its own would introduce phase error and it may be that this could be as bad as a few degrees by 6GHz. I don't see any correction polynomial for this inductance on the website and this is probably because not many VNAs support this form of correction. Most only correct for the fringe capacitance in the open.So the limitations of the kit could be influenced by this inductance for one thing. A regular Keysight 85033 SHORT will perform very well here because it uses a 3.5mm connector with an air dielectric. So there is no dielectric 'gap' at the metal plate at the end of the short as you would get with an SMA connector.

author: hendorog
author_rank: Super Contributor
timestamp: February 21, 2018, 09:14:55 pm
content: Quote from: G0HZU on February 20, 2018, 10:50:07 pmYes it's fairly experimental, but I think it should do the job.I haven't tried it in anger, but I did get it working at least - a while ago. I seem to remember I had to modify it to use a different S-param library than the one they recommend.One of these days I'll have another crack at it - I have a new contact who has a cal kit who can do the reference measurement for me.

author: G0HZU
author_rank: Super Contributor
timestamp: February 21, 2018, 09:28:47 pm
content: For my homebrew SMA cal kit here at home I used an RF simulator (that permits equations/scripts) to model the delay and the fringe capacitance and this allowed me to tweak the delay and C0, C1, C2 and C3 using a manual/iterative approach to flatten the phase error on my OPEN. It takes a couple of minutes using the UP/DWN keys on the keyboard to tweak C0, C1 etc to get it flat.The plot below shows my OPEN being compared with the model after I had optimised the coefficients in the simulator. The OPEN was measured on my ENA analyser after an Ecal and the data compare against the model. It agrees very well

author: technogeeky
author_rank: Frequent Contributor
timestamp: February 21, 2018, 11:02:34 pm
content: I just wanted to point outthese male SMA referencesavailable for about $20 in the USA.They manufacturer link goes back tomRS miniVNA Tiny and Pro's website. After more and more searching, it seems likethese guysare the manufacturer (or at least they have made measurements of the 50 ohm SMA load part).The measurements they offer arehere. I doubt this is sufficient for converting into a format you could input into a VNA characterization, but I just wanted to point out that they exist.I am going to get a pair just as an additional set of open/short/load calibrations since my current best set are homemade, and because they have them in stock in their Atlanta, GA location which is down the street from me.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: February 22, 2018, 12:06:09 am
content: G0HZUI know you're an expert on VNAs and you may remember that I bought an 8753E a while back, I also got one of the Kirkby Cal Kits. The truth is that, I never really got to understanding the calibration process properly - I'm a trained RF engineer but have forgotten a lot of things.I'd like to request that you mentor me and others here to bridge the gaps in our knowledge; if you're willing; perhaps in a new thread or we could do it here?

author: G0HZU
author_rank: Super Contributor
timestamp: February 22, 2018, 12:13:20 am
content: If choosing an alternative, a lot depends on what the kit will be used for.Option 1.If you are just going to do fairly casual 1 port VNA measurements up to 3GHz and will be typically looking at antennas or basic matching networks then you might as well make your own from modified SMA end launchers and use 2 x 100R tight tolerance (or select on test) SMD chip resistors to make the 50R load. It wouldn't be that difficult to work out a reasonable USER cal file based on guesstimates of the delays in the short and open. It would cost less than $18 even with new parts? A fairly sloppy version would work to 1GHz but something tight and tidy would be OK to 3GHz for casual measurements.Option 2.If you want to do the same but go up to 6GHz then it gets tougher and the DIY cal kit will not perform well here unless you can generate decent correction coefficients for it. This would mean you would need access to a decent VNA and cal kit to help you set up the USER cal file for the DIY kit. A step up from this would be to buy one of the little SMA kits for maybe $100 and try and tweak up the USER cal data to improve it. Even then it is going to be inferior to a proper 3.5mm cal kit from Agilent etc.Option 3.If you want to do fairly accurate 2 port modelling of DUTs then it gets a bit more serious because you might want to determine the K factor (stability) for an amplifier design for example. Or maybe measure passive SMD parts to create user models of them whilst capturing package resonances. A carefully designed and tweaked DIY SMA kit with an optimised USER cal file could just about do this up to 2 or 3GHz but if you wanted to do this to 6GHz then I think the best option is a healthy/used 85033 cal kit from HP/Agilent/Keysight. As long as it is not damaged it should work well. You would ideally need to be using expensive RF test cables up at 6GHz as well. i.e. cables with minimal phase distortion when flexed. It starts getting expensive very quickly and the cables gradually degrade (in terms of phase and amplitude stability) with regular use.Somewhere in the middle of all this is the Kirkby cal kit. You can consider it too good for option 1 and good enough for option 2. I'm not sure about option 3 if there is a 6GHz requirement. I would want a proper 3.5mm cal kit for this.

author: G0HZU
author_rank: Super Contributor
timestamp: February 22, 2018, 12:19:54 am
content: Quote from: Gandalf_Sr on February 22, 2018, 12:06:09 amThis would be best done with a youtube video but, sadly, my presentation skills and video making skills are dire so I'm not really the best person for this. You have a fabulous analyser there that is highly capable and there are loads of powerful things you can do with a VNA like that, provided you have a decent cal kit and it is set up properly. I've not used the Kirkby cal kit but I think it's safe to assume its accuracy up to 3GHz will be very good. Good enough for quite serious work. It's the performance of the kit in the 4-7GHz range I'd be unsure about. It might be really good here too but I'd expect it to need some kind of correction polynomial for the type of SHORT it uses.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: February 22, 2018, 01:38:44 am
content: OK, thanks for the advice. I'm travelling right now but I will try to re-calibrate my VNA and then ask the questions along the lines of - Am I doing it right?

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 22, 2018, 02:46:04 am
content: Anyway, tuning or modelling a diy or stray unknown kit will require a very well calibrated vna in the first place right? Not many people can do that. One of them is kirkby, other than g0hzu... if g0hzu can produce a kit with custom calibration, with proof of vna standard used and cert of calibration at cheap that will be a good option. Vna users, used or cheap version will only want a reliable kit to start with to do their job, not dicking around with sim program and no access to devices capable of modelling a kit with some level of unarguable certainties.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: February 22, 2018, 03:32:45 am
content: I got a floppy disk with calibration data on it when I bought the cal kit from Kirby.

author: KE5FX
author_rank: Super Contributor
timestamp: February 22, 2018, 04:57:20 am
content: Quote from: Gandalf_Sr on February 22, 2018, 01:38:44 amI have no idea why they're not on YouTube, but there are some videos and other material here that should be helpful:http://rfic.eecs.berkeley.edu/142/labs.html

author: technogeeky
author_rank: Frequent Contributor
timestamp: February 22, 2018, 05:17:39 am
content: Does anyone here know how long it would take to record all of the relevant calibration coefficients, if someone purchased a open-short-load and sent it to another forum member with access to a good/great VNA?At the end of the day, when is the modeling necessary? If it's only when you are making your own and trying to improve your design of DIY devices, then we can just bypass that step and send devices to people who can make the measurements for a small fee?

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 22, 2018, 05:28:57 am
content: equipments needed should be in 5 digit price. the man should have access to company's equipments, or he must already invested his own money for the cost or borrowed from friend. not to mention knowledge need to be gained so he can answer all customers inquiries about the field. how many VNA customers potentially buying the service? 10? 100 a year? $600 seems reasonable already, imho....fwiw, among other things, attached is attenuator plot provided from Kirkby to me. the result i got on my VNA is much noisier, so i know something went wrong. i'm ordering stuffs to further verify my VNA condition if its fits for measurement etc later. i hope they will not get lost during CNY...

author: hendorog
author_rank: Super Contributor
timestamp: February 22, 2018, 06:36:29 am
content: Quote from: technogeeky on February 22, 2018, 05:17:39 amYes the modelling would not be required to transfer a calibration from someone elses' cal kit.In theory, all you need to do is send them the items you want to use as calibration standards and adapters. They just need to generate an S parameter file for each one on their calibrated VNA.Then you run it through the script to determine the coefficients. How well that step works is unknown.If you also sent a decent attenuator then that could be used to compare your new calibration with the calibration of the other user.So they would need a VNA and a good cal kit. Then they would do a calibration first, and then make 5 or 6 measurements, transfer them to a PC and email them. Then ship back the items.

author: hendorog
author_rank: Super Contributor
timestamp: February 22, 2018, 06:41:15 am
content: Quote from: Mechatrommer on February 22, 2018, 05:28:57 amHe has reduced the IF bandwidth from the default. That would reduce the noise. What VNA have you got?

author: Koen
author_rank: Frequent Contributor
timestamp: February 22, 2018, 06:52:08 am
content: Quote from: technogeeky on February 21, 2018, 11:02:34 pmAmphenol 132360, 132331, 202112 maybe. I have both the kit you linked and these very-cheap three but I'm not knowledgeable enough to say anything except they look very similar.

author: technogeeky
author_rank: Frequent Contributor
timestamp: February 22, 2018, 08:35:21 am
content: Quote from: hendorog on February 22, 2018, 06:36:29 amI don't even own a VNA (though some day I would like to). But I would like information on how good a particular cal kit is, so I can understand the limitations of what measurements I can make with e.g. spectrum analyzer with tracking generator (where you normalize, so this is less important); but more importantly what the (lack of very good cal kit) reference imposed limitations are on the equipment I own (in this case, the Agilent E7459a). Most importantly, measurements of one port insertion loss and one port return loss should be calibrated, but the equipment I have was probably calibrated against a very good cal kit (more then -40dB across the almost 3 GHz spectrum) and I would like to get a sense of how far off this the instrument is, in its current state (last cal was 2011 due for re-cal in 2013). All of this in addition to using such devices for measurements.I only paid $275 for the E7495a, and I certainly can not afford anything near the cal kit that would have been included which would probably cost $1000 or more now.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 22, 2018, 11:16:30 am
content: Quote from: hendorog on February 22, 2018, 06:41:15 amDeepace KC901V. i'm start to think its a toyish VNA, but i'm not done testing yet.

author: G0HZU
author_rank: Super Contributor
timestamp: February 22, 2018, 12:11:19 pm
content: QuoteIs that attenuator (reference) plot taken with the 8720D VNA and your cal kit? Or is it a 'best' reference taken of the attenuator with the 8720 and a Keysight/Agilent cal kit? See the text below from the Kirkby website.QuoteIf a calibration kit is made using SMA F-F bullets and end caps there are a few things that will limit its performance. There will be some (extremely tiny) added inductance at the end of the SHORT and also the SMA bullet won't have a perfect 50R Zo. The SMA bullet is about 42ps in terms of delay and this is longer than a regular 85033 cal kit and so this can make any phase variation (due to imperfect 50R Zo) appear slightly worse. The 85033 cal kit uses precision 3.5mm connectors and an air dielectric and it is much better suited for use up at 7GHz.It doesn't take much to get 4 degrees of phase error over 6GHz in a DIY cal kit. If you get several degrees of phase error and it isn't corrected for by the cal kit corrections then you can expect to see that reference plot degrade a lot by 5GHz and it will get quite noisy by 7GHz. Also, an inline test of a 3dB attenuator isn't a very critical test.I can show you what my old DIY cal kit can do to 7GHz but I'll have to generate a polynomial to correct the SHORT. Otherwise it will only be good to about 3GHz. I'll have a go at changing my simulation/model to produce L0, L1, L2, L3 correction factors for my old cal kit. It should then do quite well in an attenuator test.However, I see this process as polishing a turd once you get up to 7GHz. Much better to have a decent 85033 cal kit here.

author: G0HZU
author_rank: Super Contributor
timestamp: February 22, 2018, 12:39:25 pm
content: I don't have any precision 3dB attenuators here at home but I have measured a basic SMA 3dB attenuator on my VNA and the data is below. This is after a full 2 port calibration with an Ecal module. The scale is 0.2dB/div and I used a BW of 500Hz. Note that this is after an Ecal calibration and not after a calibration with my DIY cal kit. A plot after calibrating with my DIY cal kit would have ripple on it up at frequencies above 3GHz.The attenuator isn't very accurate and is more like a 2.8dB attenuator at LF but it is rated to a high frequency.But you can see how low the ripple and noise is after a full 2port calibration for S11 S21 S12 S22. Note that I'm using Gore cables here that would have cost a 4 figure sum each here and a $13k Ecal module and a fairly decent VNA.However, a 3dB attenuator test isn't exactly a demanding proof of the integrity of a VNA calibration. There are much tougher tests than this that will show up any sloppiness in the cal kit corrections.Even an error of 0.2ps in a cal kit delay correction can be highlighted with some tests.

author: G0HZU
author_rank: Super Contributor
timestamp: February 22, 2018, 01:01:11 pm
content: I entered a polynomial for the Lx corrections for my DIY cal kit SHORT and got the result below on the simulator after a quick manual tweak. It could be better than this but I'm not really that bothered to polish it any further.I then did a full 2 port calibration using the DIY cal kit (rather than the Ecal) and remeasured the 2.8dB attenuator. So this was calibrated using my first attempt at some decent cal kit correction factors for my DIY kit. Note that this cal kit also includes my Cx corrections to get a similar flat response on the OPEN to 6GHz.See below for the result. This is actually better than I expected. If I hadn't done the Lx corrections the trace would have a LOT of ripple on it by 5GHz.

author: G0HZU
author_rank: Super Contributor
timestamp: February 22, 2018, 01:25:34 pm
content: Here's a plot of what my DIY kit looks like with only crude corrections in it. There are no Lx corrections for the SHORT and only a basic C0 correction for the OPEN. This would still be good to 3GHz as long as the various cal kit correction factors for DELAY and LOSS were correct.That's why I think anyone could make a decent DIY cal kit to 3GHz assuming they are prepared to tweak/optimise their cal kit after some tests that help to optimise it.I could put together a cal kit file with this data in it and show you the 3dB test if that helps? It would have some obvious ripple above 3GHz. However the 3dB test is a really soft test anyway.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 22, 2018, 01:34:32 pm
content: Quote from: rfspezi on February 22, 2018, 11:30:03 amits a power splitter as described by TheSignalPath. there must be detailed explanation, concept and math behind it. i will read them up when i want to make my own diy VNAor if i figure out my VNA is broken and need a tear down. fwiw i guess this type of topology that makes KC901V gives false reading esp impedance value at very low end of frequency 5KHz - 1MHz or so.Quote from: G0HZU on February 22, 2018, 12:11:19 pmhe claimed he tested all the cal kit sold to me by his own hand. incl the attenuator. so the plot you see should be unique only to my attenuator. i expect other kirkby cal kit owner should have different plot. it took long time (about a week or more) for the calibration to be made, he claimed he do this process in some quantities, to quicken his process. going to lab with my cal kit alone to do the process will take him even longer time, i take and understand this as his economical point of view. furthermore he was not well when i made the purchase i almost cancel the order because it took so long for him that i thought he gave less interest in my order. but i'm glad to support him.Quote from: G0HZU on February 22, 2018, 12:11:19 pmi'm not sure how to reply to this, just as how i'm going to reply to Kirkby in my last test, i'm not knowledgable much that i need to gain some info, do some test (or even need to have access to much expensive gears) to be able to comprehend some of the meaning. i only can hope or rely on some expert to do the testing and give some promise that it should work.btw attached (1st file) is my translation of the parameters extracted from kirkby's data relevant to my kit and VNA. for open standard, he provided varying offset delays (that i translated from offset delay ps metric in his file into mm). its varying in sub ps range or max deviation (not std deviation, maybe variance) of 0.162 mm throughout the BW. so i just prefer the mean value of 17.357 mm @ 3.5GHz (57-58 ps) to punch in the VNA if i want to do quick testing. fringing capacitance effects should already be lumped in the figures during calculation or modelling). as for short he only provided a single offset delay so i suspect the variance due to inductance effect should be negligible? i never heard of fringing inductance effect for short standardhe should provide the complete data if this is a concern. anyway this only based on trust to the expertise because i'm not at his location during the modelling. if he lied, then i liedthe 2nd attachment is the zipped s1p for my SOL kit, i dont know how to read this and not sure if its relevant to this discussion, i need time to gain on this. 3rd pdf file is my latest test report to him to seek advice. you can see S11 and S22 plot of the terminated attenuator (after calibration with his SOL kit) are quite spot on except at the area of notches which he claimed of high uncertainty even if measured with his 20GHz VNA since attenuator is terminated hence reflecting very little signal for processing. his arguments are quite rational though... and i can accept a $2K VNA will be of no match to the $17K VNA. the concern in the report is S21 you can see the noises i was talking about. he stated the attenuator should not jump up and down 5dB variance in very short BW range. i'm yet be able to reply on this before i can do more testing..Quote from: G0HZU on February 22, 2018, 12:11:19 pmthat Agilent cal kit if well within spec and in full complete data, should be about 2-3X the cost of my VNA. i can see used price is $2K already without any data. i would not give my money betting on that. ps: i'm not sure why Kirkby called his cal kit as 85033E similar to agilent naming. maybe its tracable to the agilent cal kit he owned? and his cal kit is modelled/compared after that? i'm not sure.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 22, 2018, 01:55:30 pm
content: Quote from: G0HZU on February 22, 2018, 01:01:11 pmwhat i concluded from your reply #35 and #36 is, are you suggesting that using less quality cal kit in the same VNA will result in more ripple? if that is the case, there is possibility that kirkby did the attenuator report using agilent cal kit as his calibration standard? i'll need to confirm this back to him.anyway i'm doing the test with cheap crap china sma connection and 50 ohm coax cable. maybe those also contributes to the rippling effect, i'm not sure. what i'm sure is the cabling still give consistent result even if i move them around a little bit... fwiw...

author: G0HZU
author_rank: Super Contributor
timestamp: February 22, 2018, 02:42:21 pm
content: I think your problems may be due to the type of VNA you are using. I've not seen one of those models before and it may have quite poor performance.Can you post up your Kirkby cal kit correction file or list its corrections for Cx and delay etc?I tried creating a model based on the default corrections for delay and Cx on his website here:http://www.kirkbymicrowave.co.uk/support/Kits/85033/...and then I compared this to the OPEN S1p file I found in your zip files. I assume this S1p file came from Dr Kirkby as it looks like a decent measurement to me. When I compare my model to his s1p file the phase response is very good. I'm using the Cx and delay from the web link above but you may have a tweaked version of this with your cal kit? Either way the phase response is very good and I won't post it up here because I don't want to give the impression I can measure this stuff more accurately than DrKirkby. But I will say that the results are very close! Not much to worry about here I think..I also looked at the SHORT s1p file and the results are very close to the model that is based on his default cal kit corrections on the website. This is very good indeed and it kind of shows that the SHORT in his kit is a good one I think.I can suggest subtle differences in the default Cx corrections but you probably have this info already. His kit data looks VERY good to me

author: Bud
author_rank: Super Contributor
timestamp: February 22, 2018, 02:44:19 pm
content: Do not use crappy Chinese connectors directly on your VNA connectors, you will be sorry but it will be late."Less quality cal kit" - Dr. Dunsmore of HP/Agilent/Keysight, the 8753 designer, was saying he could calibrate a VNA using a brick, as long as the brick is accurately characterized with calibration coefficients.

author: G0HZU
author_rank: Super Contributor
timestamp: February 22, 2018, 03:02:02 pm
content: QuoteI think my Ecal module 'works' because it has a lot of correction coefficients. Otherwise it would be only useful as a paperweight...

author: G0HZU
author_rank: Super Contributor
timestamp: February 22, 2018, 03:41:27 pm
content: QuoteFor sure you will get more ripple with an inferior cal kit or with one that has not been corrected properly. I can make my ENA VNA look REALLY bad if I deliberately use a poor cal kit.But I think the Kirkby kit looks OK based on the bundled S1p files. The SHORT, OPEN and LOAD s1p files look very good to me against a model based on the default cal kit data. Assuming you are setting up the transmission calibration correctly you should get very good results with minimal trace ripple in the S21 and S12 attenuator test.Note that I don't get as good a phase response as that from an Agilent/Keysight 85033 kit though. I get a virtually perfect flat phase line with the Agilent 85033 kit for the OPEN if I use the Agilent cal corrections for Cx etc in my comparison model. Note also that I'm just doing this in my workroom at home and using an RF simulator to create the comparison model. But my model seems 'perfect' when compared with the decent $$$ Agilent cal kit data and a measurement of a real 85033 cal kit on an HP8753ES as I get a flat line for the phase as per the second plot in post #15I'd be happy to review a Kirkby cal kit and I now suspect the results will be better than I first thought. However, I'd be giving it some fairly strict tests, way beyond this simple 3dB attenuator test. I'll try and borrow one of these kits from my ex colleague and put it through its paces

author: G0HZU
author_rank: Super Contributor
timestamp: February 22, 2018, 05:54:17 pm
content: I created a flawed DIY SMA cal kit correction file with performance similar to the phase plots in post#37 and see below for the result of the 3dB attenuator test after my VNA was calibrated with the same DIY SMA cal kit but it now has flawed correction data for Cx and Lx.You can see that the response has ripple above about 4GHz. Note that this has the thru delay correct and also has the loss and the basic delay correct up to about 3GHz. So it works quite well up to about 3GHz.

author: G0HZU
author_rank: Super Contributor
timestamp: February 22, 2018, 06:02:27 pm
content: I can have a play at making a quick and dirty cal kit using commercial SMA F-F bullets and a shorting end cap and a commercial SMA load and show you what happens if you just try and guess the delays based on caliper measurements and/or the typical delay in an SMA F-F barrel? This would represent about the crudest cal kit you could make for maybe <$20. The performance won't be very good but it might be fun to try this. My current SMA DIY kit uses precision end launcher connectors and this needed some adjusting with a rotary tool to get good results. But the quick and dirty cal kit described above would be made in the time it takes to screw the SMA connections together...It might not be tonight though. Any interest in this?

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 22, 2018, 06:58:14 pm
content: Quote from: G0HZU on February 22, 2018, 02:42:21 pmmaybe the attached file is what you looking for. its for agilent VNA if using my cal kit with them. its not relevant to my VNA though.. fwiw...Quote from: G0HZU on February 22, 2018, 03:41:27 pmwhat rf simulator? is this simulator accessible to mortal?can i learn? ... for the rest of your post, i need time understanding that...Quote from: G0HZU on February 22, 2018, 03:41:27 pmnow isnt that golden? (from your link abovehttp://www.kirkbymicrowave.co.uk/support/Kits/85033/)its been announced in public

author: G0HZU
author_rank: Super Contributor
timestamp: February 22, 2018, 07:45:30 pm
content: I'm using an old version of Eagleware SW for the simulator. It's old and obsolete but it supports some features that aren't in the later Keysight version of this SW and I'm using one of these (script/equation based) features to model the Cx and Lx coefficients. So it won't run on the latest version below.https://www.keysight.com/en/pc-1297125/genesys-rf-and-microwave-design-software?cc=USI checked your custom correction data for your specific Kirkby cal kit and the results for the OPEN are very good when tested for the simulator mode against the measured/supplied S1p data for the actual OPEN in your kit. I get a flat line as belowThe results for the short aren't as good because there aren't any Lx corrections in the data. But it is still good considering it is using SMA based connectors in the SHORT. It would be easy to correct this for VNAs that support Lx coefficients and if a VNA supports this feature then I guess these would be included in the data?Note that my attempts to model this stuff are fairly quick and basic. But because the results for the OPEN are spot on for both the Keysight 85033 and the Kirkby kits I suspect I've got this nailed OK

author: technogeeky
author_rank: Frequent Contributor
timestamp: February 22, 2018, 11:33:55 pm
content: Quote from: G0HZU on February 22, 2018, 07:45:30 pmJust to make sure you've seen it, have you ever looked atthisguy'sthis DIY SMA femaleandthis SMA maleopen/short/load kits? I notice that he never publishes the phase charts that you are showing.

author: G0HZU
author_rank: Super Contributor
timestamp: February 23, 2018, 12:29:06 am
content: Thanks. It's interesting to see how people approach this in different ways. I had a look at the links you gave and the IN30TD cal kit corrections have some very odd values in them. I guess there are no rules here but the numbers do seem very strange.Back when I made/optimised my DIY kit I wanted flat phase to 3GHz and low loss in both open and short. I went to fairly nerdy lengths to achieve this so I could measure/model SMD parts accurately in a test fixture with my old HP8714B VNA. I kept on refining it until it gave the performance I wanted.My cal kit cost nothing in parts because I salvaged the SMA parts but it cost a lot in time spent optimising it both electronically and with a rotary tool.

author: G0HZU
author_rank: Super Contributor
timestamp: February 23, 2018, 12:41:32 am
content: To demonstrate this I dug out an old library file of a 1000R 0805 chip resistor and this was measured with my DIY cal kit up to 3GHz.Note the scale for resistance is 5 ohm/div and it is measuring parallel Rp and Cp (not series Rs and Rs).So this should look like 1000 ohm in parallel with about 0.08pF up to about 1GHz before the parasitics begin to change things. This is with a cal kit that does not have Lx corrections for the SHORT so I had to optimise the SHORT by other means.How would this compare to others on here? Have you ever tried to measure a chip resistor like this? You need a very good VNA and an accurate cal kit and SMD test fixture to do this and get data as smooth as this over a wide bandwidth

author: G0HZU
author_rank: Super Contributor
timestamp: February 23, 2018, 12:56:41 am
content: Here's an old plot of a precision 32.4k chip resistor. I'm pushing the VNA to its limits here so the data is noisy and there will be a fair bit of uncertainty in the setup. But it managed to measure 32k4 with a flat response up to 100MHz. With a 100k resistor it gets really noisy but it does still manage to give a reasonable measurement.This is with a DIY SMA cal kit made from scrap parts but with careful manufacture and a decent USER cal file.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 23, 2018, 04:17:56 am
content: Quote from: G0HZU on February 22, 2018, 07:45:30 pmi cant see any inductance effect for SHORT in any kirkby calibration data including the master file from where everything else are derived. so i guess his measurement setup is not supporting that, or consider the effect negligible. albeit not perfect, i can say ±0.5 degree error is good enough for me i guess (my VNA systematic error will be much worse from what i figured out so far). thanks for all your reports and findings..

author: G0HZU
author_rank: Super Contributor
timestamp: February 23, 2018, 11:48:16 pm
content: That's OK. Note that I had some free time today and had a look at your male OPEN and SHORT data in your custom correction file and the bundled S1p files. The male SHORT doesn't look as good as the female SHORT in your kit. There's a bit more phase shift in the male SHORT and although it's going to be better than an uncorrected kit, I'm not so impressed with it.I generally prefer to use female cal kits because this is good for calibrating for non insertable devices that have SMA female connectors. But for insertable devices it's common to use both kits for a calibration. So I kind of ignored the male standards in your kit until today. There may be a way to improve this performance but I'd have to have one of these kits here to play with it.

author: hendorog
author_rank: Super Contributor
timestamp: February 24, 2018, 05:38:43 am
content: This is a bit left field, but bear with me as it could be a simple method to get a better characterised cal kit ...I have an SDR kits cal kit which is only supplied with electrical delay values. It has no fringing capacitance coefficents.The open standard in the kit is just a dust cap. It has no effect on the measurement, at least not significant enough to matter.Therefore the open standard is just the open female SMA adapter which I have on the port of my test set.Taking a punt here and assuming that the female SMA adapter (which came with the Rosenberger SDR kit) I have is very similar to someone elses.Therefore, could someone with a nice cal kit (G0HZU?) do me a big favour and sweep an open female SMA, and post the S1P file?Then I'll take the file, try and run it through the script and see what C0,C1,C2,C3 values come out. Then put them into the VNA and try it out.The short and load are already covered - there are no L0,L1,L2,L3 fields in the old VNA's for shorts, so I can't input those anyway.Since I already have the delay for the short, so that is the best I can do for now.I already have the SDR Kits load, as well as several non-precision 18GHz Inmet loads from eBay, out of which I have selected a few which measure quite close to 50 ohms at DC. The best I can do here is hope that they are still close enough to 50 ohms up to 6 GHz. At least they all compare sensibly with each other and with the SDR Kits load.Anyone still with me?

author: G0HZU
author_rank: Super Contributor
timestamp: February 24, 2018, 03:38:39 pm
content: Probably the most controlled way to try your experiment is to see if you can generate Cx coefficients for the Kirkby kit OPEN s1p file posted below. Then post up your Cx values here and I'll see how they perform in terms of flattening the phase? Will I see the same flat result as in post #47 for example?

author: hendorog
author_rank: Super Contributor
timestamp: February 24, 2018, 08:05:37 pm
content: Quote from: G0HZU on February 24, 2018, 03:38:39 pmWill do.I will need to setup the NLopt stuff first for the script to work. I had it setup in the past but it must have been on the laptop which died on me.

author: G0HZU
author_rank: Super Contributor
timestamp: February 24, 2018, 09:55:00 pm
content: How long does it take to run?I've added some auto optimise limits in the RF simulator to see if it can do a better/faster job than me. For my open and short I tweaked the Cx and Lx coefficients manually whilst looking at the phase. It took a minute or so to get it quite flat. With this attempt at an auto optimiser I gave it a 'bad' starting point with the phase deliberately bad and so far it hasn't managed to beat my manual attempts and it seems stuck in a rut. I think I need to tweak the optimiser a bit...

author: hendorog
author_rank: Super Contributor
timestamp: February 24, 2018, 10:42:02 pm
content: Quote from: G0HZU on February 24, 2018, 03:38:39 pmOk here is the output of the first successful run. I can see C1 has hit its limit so not expecting much...I didn't change any of the defaults for the initial settings. I suspect I will need to give it an accurate offset delay.It took several minutes, but I didn't hang around to watch. I was out of the room for 10 minutes or so.The installation of NLopt is pretty painful. There was a identifier which had changed (Octave_map vs octave_map), and some messing around with include paths etc.Attached are the graphs it produced, and below is the final output.Code:1st optimization ended with status: Optimization stopped because xtol_rel or xtol_abs was reached. (NLOPT_XTOL_REACHED)2nd optimization ended with status: Generic success return value. (NLOPT_SUCCESS)Optimization results:offs_delay = 50.000000 psoffs_loss = 5.000000 Gohm/soffs_Z0 = 50.000000 ohmC0 = -172.920826 * 1e-15 FC1 = 10000.000000 * 1e-27 F/HzC2 = -1238.347686 * 1e-36 F/Hz^2C3 = 19.888550 * 1e-45 F/Hz^3Residual RMS error : -47.880563 dB

author: hendorog
author_rank: Super Contributor
timestamp: February 24, 2018, 10:48:20 pm
content: Second run - I opened up the limit for offset delay, as the first run had hit the limit of 50ps.This completed in less than 1 minute:Code:?1st optimization ended with status: Optimization stopped because xtol_rel or xtol_abs was reached. (NLOPT_XTOL_REACHED)2nd optimization ended with status: Generic success return value. (NLOPT_SUCCESS)Optimization results:offs_delay = 55.447558 psoffs_loss = 5.000000 Gohm/soffs_Z0 = 50.000000 ohmC0 = -265.965357 * 1e-15 FC1 = -2793.805192 * 1e-27 F/HzC2 = 1240.335578 * 1e-36 F/Hz^2C3 = -194.306089 * 1e-45 F/Hz^3Residual RMS error : -53.982524 dB

author: hendorog
author_rank: Super Contributor
timestamp: February 24, 2018, 11:01:48 pm
content: Best one so far - in terms of residual. I opened up the Z0 limit, to range from 48 to 52 ohms.Code:Optimization results:offs_delay = 55.465329 psoffs_loss = 5.685029 Gohm/soffs_Z0 = 49.172627 ohmC0 = -286.232017 * 1e-15 FC1 = -2372.098441 * 1e-27 F/HzC2 = 1891.981433 * 1e-36 F/Hz^2C3 = -246.050762 * 1e-45 F/Hz^3Residual RMS error : -62.879680 dB

author: G0HZU
author_rank: Super Contributor
timestamp: February 24, 2018, 11:49:48 pm
content: The last two look the best but I'm not sure if I'm modelling the offset Zo correctly. I found that tweaking Zo improved the male SHORT Kirkby kit and that was the thing I would have experimented with if I had this kit here as per post #53.Are you optimising to 3GHz or 6GHz? Your data looks flat to 3GHz but there is a tiny slope up to 6GHz. But it still looks good.However, some of your values look strange. Normally the fringing capacitance is about 50fF but your optimiser has put in a negative capacitance of -286fF. I guess that will still be OK in the world of mathematics but can you set realistic limits for this capacitance of maybe 30fF to 100fF and run it again?On the Agilent kit this capacitance only varies by a tiny amount away from 50fF across frequency.

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 12:10:35 am
content: Quote from: G0HZU on February 24, 2018, 11:49:48 pmBy default it is sweeping over the range in the Dr Kirkby S1P file - from 50MHz to 12GHz.QuoteNo problem, I'll constrain the C values to that range and run it again. Could be just that the Dr Kirkby standards are not as mechanically 'refined' as the Agilent ones?

author: G0HZU
author_rank: Super Contributor
timestamp: February 25, 2018, 12:15:38 am
content: Here's what appears to be the custom coefficients for that Kirkby female OPEN and C0 looks to be about 44fF.QuoteI just spotted your attached results files.The optimiser tool you are using looks very powerful. I tried downloading it and the other sparam tool etc and I already have GNU Octave but I wasn't sure what to type in the command line. I tried an edited version of the default example but it didn't like it. I'm a newbie with GNU Octave so I probably haven't installed something correctly. I assume all the plots come from this optimiser tool?

author: G0HZU
author_rank: Super Contributor
timestamp: February 25, 2018, 12:20:37 am
content: Try running it up to 6GHz or maybe 7GHz as Fmax. It might give a flatter result?

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 12:32:14 am
content: Quote from: G0HZU on February 25, 2018, 12:15:38 amYes it does look very impressive. The docs are here:https://nlopt.readthedocs.io/en/latest/NLopt_Matlab_Reference/If you are on Windows, there is a page which summarises the steps. However I would not recommend trying the install just yet. I will document what I had to do as that will make it much much easier for you and anyone else to get it going.

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 12:43:10 am
content: Quote from: G0HZU on February 25, 2018, 12:20:37 amAha, I did not notice this earlier. The graphs were being output with a hardcoded and therefore incorrect frequency range which did not match the input file.I am changing the script now to use the fmin and fmax values from the S1P file.The optimiser itself uses the correct frequency range, and so this won't change the results.Here are the results from a run with the Cx values limited to the range 30-100 units. Doesn't look very good at the higher freq's.Code:Optimization results:offs_delay = 35.951981 psoffs_loss = 10.000000 Gohm/soffs_Z0 = 49.000000 ohmC0 = 100.000000 * 1e-15 FC1 = 99.011405 * 1e-27 F/HzC2 = 30.000000 * 1e-36 F/Hz^2C3 = 30.000000 * 1e-45 F/Hz^3Residual RMS error : -22.299742 dB

author: G0HZU
author_rank: Super Contributor
timestamp: February 25, 2018, 01:06:08 am
content: Yes, that looks bad at the top end. The 30.0000 values look suspicious. Has this hit a limit?I don't think you need to alter Zo away from 50R on this OPEN because DrKirkby managed to get a really flat line with Z0 = 50 in my earlier post.Can you try locking in some of his values and see if it works better with fewer variables? I'm off to bed soon so can't do much more tonight...

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 01:10:09 am
content: Quote from: G0HZU on February 25, 2018, 01:06:08 amYes that one hit all of the limits - I constrained it to 30-100 on all of the C values.I've opened them back up again and I will lock the Z0 back at 50.

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 01:11:53 am
content: Also, thanks for your help

author: suj
author_rank: Regular Contributor
timestamp: February 25, 2018, 01:38:30 am
content: For comparative purposes I've downloaded S1P for female open given by G0HZU in post #55 and checked what definitions will be generated by the tool I use. It's METAS VNA Tools II.https://www.metas.ch/metas/en/home/fabe/hochfrequenz/vna-tools.htmlThis is a powerful metrological tool focused on VNA measurements, and one of its parts is a tool for optimizing the definition of standards. The results are similar to those obtained by hendorog in post #60.

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 02:12:47 am
content: Thanks, that is interesting. They have definately found the same point.Maybe try the next one too if you have time:I did another run after removing the data > 7GHz from the S1P file. This fits much better and I think it makes more sense to use a < 7GHz fit for this kit on an 8753 for example which can't go above 6GHz.I've attached the output pdfs for a couple of new graphs I added to the script. These show the difference between the model and the s1p file and I think these are comparable to what G0HZU shows in post #47. The scale on the phase graph is +/- 1 degree though instead of +/- 5 degreesI get something similar to one or the other of the following results :-Code:Optimization results:offs_delay = 52.360635 psoffs_loss = 5.470724 Gohm/soffs_Z0 = 49.000012 ohmC0 = -226.929303 * 1e-15 FC1 = -1964.414279 * 1e-27 F/HzC2 = 2232.392337 * 1e-36 F/Hz^2C3 = -236.119457 * 1e-45 F/Hz^3Residual RMS error : -67.897497 dBCode:Optimization results:offs_delay = 34.432636 psoffs_loss = 5.643170 Gohm/soffs_Z0 = 49.000000 ohmC0 = 138.424072 * 1e-15 FC1 = -1291.076067 * 1e-27 F/HzC2 = 2442.710614 * 1e-36 F/Hz^2C3 = -217.883669 * 1e-45 F/Hz^3Residual RMS error : -67.731741 dB

author: suj
author_rank: Regular Contributor
timestamp: February 25, 2018, 02:47:36 am
content: After removing the data f>7 GHz from S1P:Here, I normalized the graph to the data from S1P:

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 03:03:19 am
content: Very nice, quite similar to the first result.Also, I just realised that METAS VNA Tools II tool you are using is free.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 25, 2018, 07:06:16 am
content: Quote from: hendorog on February 25, 2018, 03:03:19 ambut i need to email someone to get the download link. if click the download link, setupping outlook will popupi just tried copy paste the email address into yahoo mail.

author: G0HZU
author_rank: Super Contributor
timestamp: February 25, 2018, 02:45:40 pm
content: QuoteYes, your data looks much better now.That METAS VNA tool used by suj looks to be very powerful. With my simulator I had a go at plotting the fringing capacitance of the Agilent/Keysight 85033 OPEN vs frequency and I think it looks like the plot below. I hope I've got this right. It only changes a small amount and these corrections only really affect the flatness above about 5GHz.With a cheapo SMA cal kit like the Kirkby kit the SMA based standards won't have the same design integrity as a proper 3.5mm kit so the corrections are much more important because they have to correct for the flaws over most of their 7GHz range. The male SHORT in the Kirkby kit does not look good at all with its limited corrections. I couldn't live with it unless it was corrected better in the cal kit file.

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 04:26:38 pm
content: Quote from: Mechatrommer on February 25, 2018, 07:06:16 amYes, I had to do the same for gmail. That is a bit of a pain and is a very basic, manual approach they have taken to registration.No reply yet. Cutting them some slack though because its free after all and it looks really handy.They might have their hands full if all the VNA nuts on here start registering en masse.

author: suj
author_rank: Regular Contributor
timestamp: February 25, 2018, 04:38:03 pm
content: Quote from: hendorog on February 25, 2018, 04:26:38 pmI think you don't have a reply because today is Sunday and the institute is not working today. I didn't wait for the link too long.

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 04:39:41 pm
content: Quote from: G0HZU on February 25, 2018, 02:45:40 pmInterestingly we now have a way of fixing the shortcomings in the correction data. Although it won't help if the VNA doesn't support L corrections of course, which goes back to your point of needing a better constructed kit which doesn't rely on the corrections as much.Although there is always the option of dragging the data out and doing the calibration on the PC with modern software.It would be interesting to compare the Dr Kirkby coefficents with ours on a tighter vertical scale on the same graph to see if there is any significant advantage one way or the other.

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 04:42:41 pm
content: Quote from: suj on February 25, 2018, 04:38:03 pmYes - it is pretty clear based on the email method and the delay over the weekend. The registrations are processed manually.AI hasn't taken over yet

author: G0HZU
author_rank: Super Contributor
timestamp: February 25, 2018, 05:34:31 pm
content: If you haven't downloaded it already here is the bundled s1p custom data on the Kirkby male SHORT in a text file and I've listed the custom corrections below.QuoteThere is only a delay correction and I get the phase response below. This does not look good but I guess the male part of the kit will be used less often. The older 8753 VNAs kind of default to 'insertable device' calibrations so they would often use both male and female kits for a full two port calibration. In this case it's debateable if the Kirkby kit is 'fit for purpose' for a decent 6GHz lab VNA like an 8753?

author: G0HZU
author_rank: Super Contributor
timestamp: February 25, 2018, 05:51:58 pm
content: With my manual optimiser for the Lx corrections I can flatten the response and it's easier if I drop the Zo slightly. But I get a slight fixed phase offset with the flat response. Not sure what has happened there. Maybe it needs to be measured again on a VNA?How does it look if you try and optimise it with METAS?It looks better with just a Zo tweak but maybe also try it with Lx corrections. It's a shame this Lx correction can't be added to the 8753 firmware in some way. It might be possible to bodge it in to the firmware with a crude patch?

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 05:53:30 pm
content: Quote from: G0HZU on February 25, 2018, 05:34:31 pmYes I think you have a point. Even with corrections it is not great.This is what the optimiser spits out when I remove the data above 7GHz. L1 has hit the limit.Code:offs_delay = 54.877614 psoffs_loss = 2.058719 Gohm/soffs_Z0 = 51.050105 ohmL0 = -3687.287669 * 1e-12 HL1 = 10000.000000 * 1e-24 H/HzL2 = -978.814153 * 1e-33 H/Hz^2L3 = 2713.293761 * 1e-42 H/Hz^3Residual RMS error : -48.553224 dB

author: suj
author_rank: Regular Contributor
timestamp: February 25, 2018, 06:28:51 pm
content: Quote from: G0HZU on February 25, 2018, 05:51:58 pmResults from Metas. A better result if the optimizer can change "Offset Z0" - column "Agilent definition". Anritsu and R&S probably don't support Z0 changes and the effects can be seen for Z0 = 50 Ohms.Normalized to S1P.Black - data from S1PRed/brown - HP (with optimized Z0)Orange - fixed Z0

author: suj
author_rank: Regular Contributor
timestamp: February 25, 2018, 06:56:22 pm
content: Quote from: G0HZU on February 25, 2018, 05:51:58 pmBy the way. It should be possible to do it off-line with Metas. It has a built-in driver for the 8753 and 8720 series (as well as 8510C, ENA, PNA). You can make measurements and off-line error correction using this software. Definitions of the "short" element that you can prepare have the option of defining L.The procedure is shown in the tutorial on the program's website.It looks like a Swiss army knife

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 07:03:28 pm
content: Quote from: suj on February 25, 2018, 06:56:22 pmBingo. I was thinking of using scikit-rf, but Metas would no doubt be more straight forward.Really looking forward to getting hold of it.

author: G0HZU
author_rank: Super Contributor
timestamp: February 25, 2018, 07:22:10 pm
content: QuoteWow, that sounds great. I hope to get a copy of METAS soonSee below for a quick and dirty OPEN and SHORT made from a pair of SMA F-F bullets. One has a commercial SC end cap for the short. Sadly, the two bullets are from different manufacturers so they are not going to be the same but the end cap for the short is a known part and it isn't expensive. Maybe $9?So maybe if I buy some Amphenol SMA F-F bullets from Farnell ($8 ea?) we could have a go at making a cheap cal kit for the masses?But for now, have a go with METAS to see how flat you can get the phase data for these two bad boys below?

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 07:23:09 pm
content: I was having a heck of time with this one. The fit wasn't lining up with the Metas one by sujThen I found a bug in the model calculation for the Lx params. Fixed that and tada, now it lines upAlthough it does tend to find another result at 53 ohms Z0. This one took a bit of nudging.Code:Optimization results:offs_delay = 32.331122 psoffs_loss = 6.333923 Gohm/soffs_Z0 = 60.858025 ohmL0 = 872.429450 * 1e-12 HL1 = 5981.654164 * 1e-24 H/HzL2 = 37028.127991 * 1e-33 H/Hz^2L3 = 3160.750516 * 1e-42 H/Hz^3Residual RMS error : -53.679006 dB

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 07:54:24 pm
content: Quote from: G0HZU on February 25, 2018, 07:22:10 pmI did a bit of blue sky thinking:There is nothing preventing us from having different coefficients for different frequency ranges.The fit will be better by limiting the frequency range it is over.Also, if the cal is done offline in software, then changing coefficients (i.e. recalibrating using a different set of coefficents) is purely software and doesn't require another sweep. So it would be technically possible to do a full sweep and change cal definitions on the fly. The definitions would match the real cal standards very closely.In fact I expect this could be as good or better than a high quality cal kit - assuming it only has one set of coefficents for the entire range of the kit. Perhaps this is how the eCal units work?

author: suj
author_rank: Regular Contributor
timestamp: February 25, 2018, 08:07:44 pm
content: Quote from: G0HZU on February 25, 2018, 07:22:10 pmTwo cases for the "open" element and two for the "short" element. For each element once Z0 opened and once set to 50Code:Agilent DefinitionStandard Type:OpenOffset Z0 (Ohm):60.711892Offset Delay (ps):27.289762Offset Loss (GOhm/s):3.507799C0 (E-15 F):414.232256C1 (E-27 F/Hz):-6871.633507C2 (E-36 F/Hz^2):-4959.099088C3 (E-45 F/Hz^3):470.623016Agilent Fit ErrorRMS Error0.001900Max Error0.003349_______________________________________________Agilent DefinitionStandard Type:OpenOffset Z0 (Ohm):50.000000Offset Delay (ps):58.437897Offset Loss (GOhm/s):2.711473C0 (E-15 F):-304.566047C1 (E-27 F/Hz):-8873.121112C2 (E-36 F/Hz^2):2622.781977C3 (E-45 F/Hz^3):-343.691735Agilent Fit ErrorRMS Error0.002197Max Error0.003648_______________________________________________Agilent DefinitionStandard Type:ShortOffset Z0 (Ohm):56.059063Offset Delay (ps):41.557996Offset Loss (GOhm/s):3.717653L0 (E-12 H):-222.842514L1 (E-24 H/Hz):-19759.249841L2 (E-33 H/Hz^2):11091.105982L3 (E-42 H/Hz^3):-651.849387Agilent Fit ErrorRMS Error0.001378Max Error0.003844_______________________________________________Agilent DefinitionStandard Type:ShortOffset Z0 (Ohm):50.000000Offset Delay (ps):32.074189Offset Loss (GOhm/s):4.973737L0 (E-12 H):492.787861L1 (E-24 H/Hz):-6736.857074L2 (E-33 H/Hz^2):-3868.927304L3 (E-42 H/Hz^3):506.666193Agilent Fit ErrorRMS Error0.001556Max Error0.004609Open element, Z0 open:Open element, Z0=50:Short element, Z0 open:Short element, Z0=50:

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 08:18:50 pm
content: See if you can manually scale the normalised phase charts - the glitch is killing all of the detail due to the auto scaling.From what I am seeing it is hard to get a good match 0-6GHz. Much better dividing into 0-3GHz and 3-6GHz.

author: suj
author_rank: Regular Contributor
timestamp: February 25, 2018, 08:20:33 pm
content: I think I need to change the way the phase is displayed. Error during changing the phase from -180 to +180 obscures the situation.

author: G0HZU
author_rank: Super Contributor
timestamp: February 25, 2018, 08:26:46 pm
content: Hi suj, thanks for putting the data into METAS.I noticed that the loss response of that SMA F-F (OPEN) on S11 looks a bit poor up to 3GHz and I tried another SMA F-F bullet and this one looks better. Both are clean and look similar but one has lower loss. I assume there must a difference in materials used and/or subtle differences in Zo along the connector.QuoteThat would be neat, I'd definitely be interested in being able to do this. My original DIY SMA kit must be about 12 years old now and it would be nice to retweak the corrections for any wear. I spent ages optimising the cal kit for it when I first got my HP8714B VNA and this involved lots of repetitive tests and calibrations. I don't really want to do this the hard way again.I've dug out the HP8714B from under the stairs and powered it up for a bit of nostalgia. I do like the big old CRT display on it even though it is just mono.

author: in3otd
author_rank: Contributor
timestamp: February 25, 2018, 08:34:37 pm
content: Quote from: hendorog on February 25, 2018, 07:23:09 pmuh, oh, you mean the indices of the Lx coefficients were off by 1in thestd_model_s_params()function, right? I'll upload a corrected version shortly, thanks!

author: suj
author_rank: Regular Contributor
timestamp: February 25, 2018, 08:34:47 pm
content: Hi,I changed the files on my server. After refreshing, the normalized data should look OK.

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 08:37:44 pm
content: Quote from: in3otd on February 25, 2018, 08:34:37 pmHaha, welcome! I was considering sending you an email to let you know we were discussing your code here!Yes that was the issue. I just figured you hadn't used L params much due to the 8753 et al not supporting them.

author: in3otd
author_rank: Contributor
timestamp: February 25, 2018, 08:51:39 pm
content: Quote from: hendorog on February 25, 2018, 07:54:24 pmIf you have a VNA where you can access to the calibration coefficients, like the 8753 and, I think, most of the ones not targeted at hobbyists, you can simply use something like scikit-rf to do the calibration using the calkit S parameters directly (no need of building any model of them) and then write the computed calibration coefficients back to the VNA. I don't know if this is what the METAS VNA Tools can actually do or if it allows only a post processing of raw data acquired from the VNA.Then another issue is the calkit repeatability, with cheap stuff you never know how it will behave tomorrow

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 09:09:39 pm
content: Quote from: in3otd on February 25, 2018, 08:51:39 pmYes, very true. In this way we can remove the model entirely.With the cal kit repeatability issue, I think that is where buying high quality open/shorts and characterising them should produce a better result than DIY.Also, the proposal I mentioned a while back, was to not use an open standard at all when the VNA has a female SMA port.As long as it is characterised then is there any point in connecting a standard to it, aside from a slight noise reduction? This is one less connection to make when calibrating.I need an s1p file from a calibrated VNA which has a female SMA port left open. Since we have optimisation software, I will try to create a model for it.

author: G0HZU
author_rank: Super Contributor
timestamp: February 25, 2018, 10:07:48 pm
content: QuoteI've done that with a known SMA barrel at the end of an SMA cable and I have a very 'short' male SHORT made from a cut down Suhner (good quality) SMA connector. See the image below.It is possible to just use an SMA end cap for the short instead but the end cap will obviously spin as it is being undone so this can cause wear. The short below has a nut that can still spin (so no wear issues) but this means it has some delay in it and the performance isn't great and I don't use this very often and I try to only use it below 1GHz.

author: hendorog
author_rank: Super Contributor
timestamp: February 25, 2018, 10:32:55 pm
content: Quote from: G0HZU on February 25, 2018, 10:07:48 pmFor the short I was intending to use these parts. These are the ones used in the SDR kits. I have one of their Male kits so I already have the male short below.Female short:http://sdr-kits.net/documents/32Z114-000L5.pdfMale short:http://rosenberger.de/ok/images/documents/db/32Z111-000L5.pdfThe wear issue is a bit tricky. I believe the Male below can spin internally (am not near it right now to verify), but the Female obviously can't and so would need to be held still while the nut is tightened. The specs for both say 500 mating cycles. However I am sure they will change their characteristics over their lifetime - as in3otd alluded to.

author: hendorog
author_rank: Super Contributor
timestamp: February 26, 2018, 04:53:53 am
content: Quote from: Mechatrommer on February 22, 2018, 01:55:30 pmI just took a closer look at your attachments in the post above this one.Few comments which hopefully will help:* The attenuator return loss measurements, with the free port terminated, is probably not too bad given the device. The return loss of that attenuator with attached terminator is probably pushing the limits of your device.* The Dr Kirkby data and method you have to use (i.e. using the terminator) don't seem to line up with what he has in his FAQ:http://www.kirkbymicrowave.co.uk/FAQ/How-do-I-verify-the-calibration-kit-is-working-properly/* The S21 measurements are probably poor as the Deepace doesn't seem to support a 'full 2 port' calibration. Do you know if it supports a full 2 port calibration, or is it just a 'response' calibration? In The Signal Path youtube review it shows a simple response cal only with a through.* A full 2 port cal can correct for many more errors than a simple response cal can. Since you are using a lower cost, compact device which doesn't have great directivity and port return loss, then you will really need this error correction to get decent results on the S21 test.* If you can pull the raw data out of the device and get it into touchstone format, then you should be able to use scikit-rf or Metas to do the full 2 port cal.* According the manual it supports using an external bridge/coupler. Sometimes high quality ones come up on eBay which have come from HP gear.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 26, 2018, 05:32:41 am
content: Quote from: hendorog on February 26, 2018, 04:53:53 ami did exactly according to that in my first report to him (see attached version 1 report fwiw). the S11 or S22 (just turning the attenuator upside down on the same VNA port 1) was totally out. in our email conversation he admitted the mistake of procedure in his link and said he will edit the link, but it seems he havent. he asked me to do the test again with attenuator terminated. with attenuator's end dangling opened (like in the link), the reflection from opened end will affect to the port under test on the under end, something like that according to him.Quote from: hendorog on February 26, 2018, 04:53:53 amcorrect, there is no directional coupler (or power splitter) on the other port 2 of the VNA, so it can measure S21 only but not true S12. i have to turn the DUT around to simulate S12. i guess the VNA will try to solve half part of the full 4 port parameter matrix.Quote from: hendorog on February 26, 2018, 04:53:53 amwhat raw data? sorry noob question. but i dont think i can extract anything from the device other than its measurement result.Quote from: hendorog on February 26, 2018, 04:53:53 amthanks for reminding me this. i will study more on this.ps: albeit more ripples on the output of the KC901V VNA, similar to G0HZU simulation on poorly tuned cal kit, i think we can still do some regression or averaging in our head on the result, since its still following the main path if we can see in G0HZU's report pictures reply #35, #36, #44 overlapped (2nd attachment). so i hope my VNA will give not entirely useless result. i just have to "assume" of lesser ripple in the final output. my further test and measurement will confirm this hypothesis true or false as i go, i just have to understand my tool better. ymmv.

author: hendorog
author_rank: Super Contributor
timestamp: February 26, 2018, 06:02:38 am
content: Quote from: Mechatrommer on February 26, 2018, 05:32:41 amYep makes sense.Quote from: Mechatrommer on February 26, 2018, 05:32:41 amIf you extract the data then you can still do better using scikit-rf. It supports a calibration type called 'Two Port one Path' or something like that. Basically you can do a full 2 port cal with only one directional coupler. You do need to swap around the DUT to measure both ports.However to do this, first you need to be able to extract the raw data for the sweeps and transfer it to a PC. Then use software on the PC to do the calibration instead of using the software inside the KC901V.Quote from: Mechatrommer on February 26, 2018, 05:32:41 amCheck the 'Data Saving' section of the manual. I found it online, apparently you can export s1p data files to an SD card in the smith chart mode.Without doing a cal of the device, you do a sweep of your cal standards, and export them each into different files - i.e. short.s1p, open.s1p, load.s1p, thru.s1p and the device you want to test dut.s1p. Then you should be able to use those files containing 'raw data' with software like scikit-rf or Metas to do a calibration and measure the device on your PC.Note I haven't done this myself - yet - so ymmv.

author: in3otd
author_rank: Contributor
timestamp: February 26, 2018, 07:56:30 am
content: Quote from: rfspezi on February 18, 2018, 10:25:21 amThere is a description about using Rosenberger parts, similar to the ones in the SDR-Kits, as calkit, seehttp://www.hhft.de/index.php?page=competences&subpage=calibration. They just use the offset lengths to describe the standards and leave all the Cx and Lx to zero. It may not be so important to split the femtofarad if you go up to 5 GHz - any excess capacitance or inductance can probably taken into account by adjusting the offset length only.

author: hendorog
author_rank: Super Contributor
timestamp: February 26, 2018, 08:03:01 am
content: Metas download link has landed in my spam folder this evening (I use gmail)So anyone that is waiting, might be worth checking there.

author: hendorog
author_rank: Super Contributor
timestamp: February 26, 2018, 08:18:18 am
content: Quote from: in3otd on February 26, 2018, 07:56:30 amNot sure if you have seen this info :- SDR kits actually publish reasonable delay info, and the part numbers of the Rosenberger parts they use. It used to be really difficult to find on their old website but its better now. There is also a document explaining how they got those values. Unfortunately they don't provide the s1p/s2p files or we could use them with your script to get the missing info.https://www.sdr-kits.net/index.php?route=web/pages&page_id=36_36https://www.sdr-kits.net/documents/Rosenberger_Fairview_Male_Cal_Standards.pdfhttps://www.sdr-kits.net/documents/Rosenberger_Female_Cal_Standards_rev4.pdf

author: in3otd
author_rank: Contributor
timestamp: February 26, 2018, 09:04:30 am
content: Quote from: hendorog on February 26, 2018, 08:18:18 amyes, I should have started my message saying "in addition to the well know calkit from SDR-Kits, which comes wit some modeling data".A few years ago I exchanged a couple of emails with Kurt Poulsen (which prepared the SDR-Kits calkit docs), when I saw a message he posted to the VNWA Users Group on Yahoo saying that had measured the S-parameters of the Amphenol Connex and Rosenberger calibration kits; I don't remember if he also sent me the related .s1p/.s2p files, need to check my old emails.Anyway, it would make sense to tell the SDR-Kits people that making the measured calkit data available may help in selling more kits.

author: hendorog
author_rank: Super Contributor
timestamp: February 26, 2018, 09:16:39 am
content: Quote from: in3otd on February 26, 2018, 09:04:30 amHeheI was just trawling through his website after reading your post. In one of his older docs he actually points to that same website and shows some of their dataIt would be great if they did. There are so many 8753's around that the prices have dropped even on eBay - which is the opposite of just about everything else there! There are just no cal kits to go with them (or test sets... sigh...) I'm sure they would sell quite a few of them.My cal kit box has s/n #28 on it, from about 2015. I wonder what number they are up to now...

author: suj
author_rank: Regular Contributor
timestamp: February 26, 2018, 01:21:19 pm
content: There is one type of calibration kits, that you can easily prepare yourself. Below the X band, waveguides are rarely used, so rather unhelpful for 8753. I have 8510C which supports TRL calibration. I needed to measure the WR90/WR75 adapter. I had the calibration kit WR90 but I missed the WR75. That's what I decided to build. I ordered machining on Wire EDM. I made the finishing of the surface with sandpaper and polishing paste. The determination of coefficients is pure geometry. I measured the length of the 1/4 lambda line with a micrometer. In the most simple case (if we do not measure the insulation), such a kit consists of two elements - short (wall closing the waveguide) and a section of waveguide 1/4 lambda. Inexpensive, quite easy to do and work - I compared the results with Maury X7005E WR90 kit.And the most important thingIt must have a wooden box.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 26, 2018, 02:20:02 pm
content: Quote from: hendorog on February 26, 2018, 06:02:38 ami think this is the missing piece for me to all of your discussions here, thanks i'll try to catch up. but the downloaded META VNA Tools II only works on Windows later than Vista, so my WinXP cant installed, anothermoment... i'll try install it in another Win10 PC.Quote from: hendorog on February 26, 2018, 06:02:38 amcorrect. i'll study this more seriously when i got installed any VNA tools. thanks.

author: hendorog
author_rank: Super Contributor
timestamp: February 26, 2018, 07:56:49 pm
content: Quote from: Mechatrommer on February 26, 2018, 02:20:02 pmCool.Now that I have Metas I think you are better off using scikit-rf for this type of thing. Metas is obviously targeted at Metrology and lab work, and as such is very 'rigorous' in its processes. Having worked in a lab (food not RF!) before I recognise the focus on recording everything, traceability of measurements, cables and adapters used for the measurement etc etc.I am not even sure yet what it can and can't do! This is just my impression from using it once so ymmv.scikit-rf is a much more techy to get installed and working, but has more flexibility so I will use that for experimentation.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 27, 2018, 03:51:59 am
content: Quote from: hendorog on February 26, 2018, 07:56:49 pmi am heavy butt lazy arse nowadays that i expect a ready made exe, i dont have much more time for long step by step install of Anaconda, Phyton learning etc. but i'll try that if i cant work out META... thanks.

author: hendorog
author_rank: Super Contributor
timestamp: February 27, 2018, 04:28:47 am
content: Quote from: Mechatrommer on February 27, 2018, 03:51:59 amYeah I can understand.It actually was quite straightforward though as anaconda takes care of installing python, scikit-rf and all of the dependancies, including a simple IDE. Certainly it is much easier than back when anything python related had to be installed manually, package by package. Now that was a pain in the a$$.

author: hendorog
author_rank: Super Contributor
timestamp: February 28, 2018, 08:34:40 am
content: New thread with install guide for the IN3OTD script is here:https://www.eevblog.com/forum/rf-microwave/vna-cal-kit-modelling-script-install-guide/

author: hendorog
author_rank: Super Contributor
timestamp: February 28, 2018, 10:54:03 pm
content: In other news, on his Test Equipment group Dr Kirkby offered a couple of out of spec cal kits at a low price.Since these come with s-params I grabbed one of them. Shipping is very high, but ultimately still worth it for me to have items which I can use as a calibrated reference.https://groups.io/g/Test-Equipment-For-Sale-Wanted-or-Exchange

author: TheSteve
author_rank: Unknown
timestamp: February 28, 2018, 11:04:27 pm
content: Quote from: hendorog on February 28, 2018, 10:54:03 pmThe question is, did you pay soon enough to get one of the sets. I know I paid for one 14 hours ago.

author: hendorog
author_rank: Super Contributor
timestamp: February 28, 2018, 11:28:22 pm
content: Quote from: TheSteve on February 28, 2018, 11:04:27 pmYeah I have one of them locked in. I was in a meeting at the time and was surreptitiously putting a payment through on Paypal while nodding my head and looking interested in what was being said. No idea what I have promised to deliver on, but hey at least I'll have a cal kit.Then I screwed up the email address and had to cancel the payment and put it through again. It was about 23 hours ago.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 28, 2018, 11:35:31 pm
content: Congratulation for your score. When i made the purchase, i wish i can have yellow case instead of black. But i choosed cheaper option of 'whatever color mostly in stock'. In the end i got... yellow case

author: hendorog
author_rank: Super Contributor
timestamp: March 01, 2018, 12:21:27 am
content: Quote from: Mechatrommer on February 28, 2018, 11:35:31 pmThanks

author: G0HZU
author_rank: Super Contributor
timestamp: March 01, 2018, 01:17:16 am
content: QuoteI'm not convinced you can treat the Kirkby kit as some form of calibrated reference if you want to start playing with Cx and Lx factors. I'm not an expert on SMA-SMA connector variability but you can't avoid having a subtle discontinuity between your SMA test cable and the Kirkby SMA cal connector because you can't expect two solid dielectric connections to mate perfectly without a tiny (uncontrolled) air gap and without some form of pin mating variability as well. So I don't know how much this will affect the phase response across a 6GHz bandwidth. A 3.5mm to SMA connection should be a lot better in this respect.

author: hendorog
author_rank: Super Contributor
timestamp: March 01, 2018, 01:33:53 am
content: Quote from: G0HZU on March 01, 2018, 01:17:16 amHmm, that is an interesting point and something I don't know enough about to understand how to mitigate.However, I do have some nice Gore 3.5mm M-M cables (I have been too scared to use them so far) which I can use to mate with the female type standards. Should I get some 3.5mm F-F barrels for the male type standards? I need some anyway as I have an old 8515 test set I want to play around with.I assume the other side of this is what was used on the other end when they were swept. I can ask the question.

author: G0HZU
author_rank: Super Contributor
timestamp: March 01, 2018, 02:15:58 am
content: Also, an SMA female inner expands as it is mated so the Zo (subtly) changes depending on mating depth and male pin diameter. The 3.5mm connector has a solid outer so this problem goes away.I just think that once you get past 2 or 3GHz you reach the point where you are trying to polish a turd if you want to try and 'calibrate' an SMA based standard using Cx and Lx corrections.I've always had decent results with my DIY female SMA cal kit but this was only up to the 3GHz limit of my old HP8714B VNA. Also, a lot depends on how accurate it all really needs to be. I suspect that you can get away with using an SMA based cal kit up to 7GHz if you just want to make casual measurements and can accept a lot of uncertainty.Has anyone tried doing an 'insertable device' calibration using both the male and female parts of the Kirkby kit up to 7GHz and them done some critical tests? Even the basic 6dB attenuator test would be interesting to see.

author: hendorog
author_rank: Super Contributor
timestamp: March 01, 2018, 02:25:42 am
content: Quote from: G0HZU on March 01, 2018, 02:15:58 amYes that makes sense. I was going to bypass the Cx Lx issue by doing calibrations offline on a PC where I want the best precision, but it will still be limited.While on the subject of 3.5mm - I wonder how much better 3.5mm F-F would they be as cal standards if you used them instead of the SMA F-F bullets in post #86??The end cap could still be SMA I assume as it won't ever be moved. Do you have any you could sweep?They are much more expensive of course, 100 USD on digikey/mouser. But still that is cheap in relative terms.

author: G0HZU
author_rank: Super Contributor
timestamp: March 01, 2018, 02:42:09 am
content: I've got one at work but someone has borrowed it. Also, I haven't inspected it for quite a while to see how healthy it is. It's very old and has seen a lot of use. I'll try and find it tomorrow.

author: G0HZU
author_rank: Super Contributor
timestamp: March 01, 2018, 02:59:37 pm
content: OK I found it at work today. I had to walk 1km into a horizontal blizzard to get it as it was being used at another company siteIt's a 3.5mm F-F connector but not the same grade as the 3.5mm connectors in a typical Agilent cal kit as it uses expanding female contacts rather than the delicate solid centre (with inner petals) as per an Agilent cal kit. So it might not be that much better than an SMA F-F connector, especially as this one is very old and probably quite worn. But I've cleaned it and I'll try it later today. It's really cold and snowy here in the UK and we've been sent home from work early today and told that we don't have to go back until MondayI'll have an initial look at this connector once my VNA has warmed up.

author: hendorog
author_rank: Super Contributor
timestamp: March 01, 2018, 05:50:12 pm
content: Quote from: G0HZU on March 01, 2018, 02:59:37 pmNow that is dedication!

author: G0HZU
author_rank: Super Contributor
timestamp: March 01, 2018, 10:08:31 pm
content: It's really cold here because of the gusty wind chill factor and it's hard to keep the house warm. However, I've measured the 3.5mm F-F bullet and the files are below. Note that the room is not that warm even with the test gear on so I don't know if the VNA and Ecal will be stable and OK. Plus this type of measurement really should be done in a proper metrology lab and not with my gear in a spare room in a house.But here are the results for the 3.5mm F-F left open and with the shorting end cap fitted. The results are fairly good but maybe not as good as I'd expected. I'm off to sit by the fire... the strong winds are sucking the heat out of the house like blowing cold air on a heatsink!

author: TheSteve
author_rank: Unknown
timestamp: March 11, 2018, 05:01:24 am
content: My very budget Kirkby kit - I added the USB drive, male and female through's and Pelican case.

author: hendorog
author_rank: Super Contributor
timestamp: March 11, 2018, 05:33:08 am
content: Quote from: TheSteve on March 11, 2018, 05:01:24 amNice oneI didn't go for the case or the usb stick. I did get the attenuator and the thru's though.Mine is still some way away though. I really should use the time to build a case

author: TheSteve
author_rank: Unknown
timestamp: March 11, 2018, 06:28:40 am
content: Quote from: hendorog on March 11, 2018, 05:33:08 amWhen I say I added the USB drive and Pelican case I was meaning I added it myself. I already had an extra Pelican 1020 sitting here, same as Dave uses.

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 11, 2018, 07:10:54 am
content: Quote from: TheSteve on March 11, 2018, 06:28:40 amdid the cal kit comes with calibration data? if not, how are you going to calibrate it?

author: TheSteve
author_rank: Unknown
timestamp: March 11, 2018, 07:11:55 am
content: Quote from: Mechatrommer on March 11, 2018, 07:09:50 amDr Kirkby is emailing me the file for my specific kit to load into my FieldFox.

author: TheSteve
author_rank: Unknown
timestamp: March 11, 2018, 07:51:50 am
content: Here is a shot of a Mini Circuits 10 dB 0-6 GHz attenuator. Note the scale is 0.2 dB per division. I really need some phase stable cables!edit - added the 20 dB one as well.

author: hendorog
author_rank: Super Contributor
timestamp: March 11, 2018, 10:43:38 pm
content: Quote from: TheSteve on March 11, 2018, 07:11:55 amWhen you get the s1p files, can you post them please? I would like to compare them with mine when it arrives.Also, out of interest which type of through calibration did you use for the attenuator pics?(1000th post whoop whoop!)

author: TheSteve
author_rank: Unknown
timestamp: March 12, 2018, 12:23:28 am
content: Quote from: hendorog on March 11, 2018, 10:43:38 pmSimply normalized the system.

author: G0HZU
author_rank: Super Contributor
timestamp: March 12, 2018, 01:39:44 am
content: Try clamping the cable ends so they can't move during the calibration.Here's a 6dB attenuator measured using the crappiest SMA cables I have here. These are used/salvaged cables that cost less than £1 each on ebay and they are old but made with decent quality SMA elbow connectors. But the cable is regular skinny low cost cable.See below for the attenuator response to 6GHz and how feeble these old cables are. But I still got a good result with a bit of care wrt not moving the cables during the full 2 port SOLT calibration.

author: hendorog
author_rank: Super Contributor
timestamp: March 12, 2018, 02:15:18 am
content: Quote from: G0HZU on March 12, 2018, 01:39:44 amQuote from: TheSteve on March 12, 2018, 12:23:28 amI think the difference is ^^^

author: G0HZU
author_rank: Super Contributor
timestamp: March 12, 2018, 02:45:37 am
content: The poor plots were blamed on poor phase stability so I assumed some form of SOLT calibration had been done. What's the point of posting up the attenuator plot if it wasn't made with the Kirkby cal kit? I'm lost...I also don't see the point of posting up a plot to 6GHz using poor cables and a normalisation. The mismatch uncertainty during the through cal ought to be the main problem, not phase stability. Maybe try it again using attenuators at the cable ends during the thru cal. This will improve the port match.

author: TheSteve
author_rank: Unknown
timestamp: March 12, 2018, 03:47:13 am
content: Quote from: G0HZU on March 12, 2018, 02:45:37 amIt is fair you are lost. The post was largely irrelevant, just got caught up playing with my toys, sorry guys.As far as a cal goes for S21 the only cal option I have is to normalize. The FF I have does not do S12/S22 nor phase with S21.I can do the full OSL for S11 of course.With respect to the attenuation plots it is quite easy for me to shift the plots around by moving the cable, I did switch to another which isn't as sensitive but it is still easy to see changes.edit - G0HZU - the plot you made looks great. Do you know what(if any) kind of averaging or smoothing your analyzer is doing? I can easily make my plots look significantly better with just a little bit of smoothing added in firmware.Added an example showing S21 and S11(well within the spec of the Mini Circuits attenuator), OSL cal for S11, normalize for S21, smoothing turned on).

author: hendorog
author_rank: Super Contributor
timestamp: March 12, 2018, 04:12:16 am
content: Quote from: TheSteve on March 12, 2018, 03:47:13 amIf you can get all of the data out of your FF then you could have a go at using scikit-rf for the 'one path 2 port' cal.I will be doing the same when my cal kit arrives and I'm happy to give it a go as a test run if you post all of the files. I don't have a test set, am just using a coupler.

author: G0HZU
author_rank: Super Contributor
timestamp: March 12, 2018, 05:21:15 pm
content: QuoteRBW is 1kHz and averaging and smoothing both set to off.

author: mgberry
author_rank: Newbie
timestamp: March 14, 2018, 11:16:01 pm
content: Great thread on the Kirkby kit. I thought I would throw in my experience as well. I purchased one his kits awhile back and did some measurements using my 85052b and N5221A. My observations were that for a low cost kit it performed pretty well below 3Ghz. I found some challenges above 3Ghz that were basically what you guys have observed. The two things that stood out were inductance issue and connector repeatability. Overall I thought it was a reasonable buy for a low cost kit....of course this is prior to the price hike.Matt...Would be glad to make some measurement for anyone that needs additional data points of the kit.

author: G0HZU
author_rank: Super Contributor
timestamp: March 16, 2018, 07:49:28 pm
content: Hi MattCould you use both the male and female parts of the Kirkby kit to do a 2 port cal for an insertable device? i.e. measure something like an inline SMA 6dB or 10dB attenuator up to 6 or 7GHz?Then maybe repeat using a different set of SMA test cables to see if the results are repeatable across different mating SMA connectors. You may have done this already and it would be interesting to know what results you got.I'm not convinced that an SMA cal kit will give repeatable results up in the 3-7GHz region when mated with various makes of SMA cable because of the undefined air gap between the solid dielectrics once the connectors are mated. I think it will be fine to about 3GHz and it already looks like you have reached similar conclusions.

author: TheSteve
author_rank: Unknown
timestamp: March 17, 2018, 08:21:38 am
content: Just as a quick followup here is what I have been able to achieve using the Kirkby out of spec SMA cal kit(good to 3 GHz, not 7 GHz) with my N9912A FieldFox handheld analyzer.Port 1 OSL performed, then normalized to port 2.Mini Circuits VAT10+ 10dB attenuator.First capture with 5% smoothing, no averaging.Second capture no smoothing, no averaging.edit - added the same captures with VAT20 20 dB and VAT30+ 30 dB attenuators, I only have one of each to measure.

author: rfspezi
author_rank: Regular Contributor
timestamp: March 19, 2018, 08:06:25 pm
content: I could need some advice on what i am doing wrong with my Kirkby cal-kit.(Please appologise stupid questions, since VNA measurements are totally new to me)My setup consists of:-) HP 8753E VNA (6 GHz)-) Kirkby 85033 SMA calkit-) 50 cm RG316D koaxI followed the instructions on the Kirkby 8753 page here:http://www.kirkbymicrowave.co.uk/support/VNAs/HP-Agilent-Keysight/8753/On the floppy disk there are 3 files (SMA, SMA_M_M, SMA_F_F).I selected "SMA" and loaded it with "RECALL STATE".Is that the correct file to choose?After that, the frequency range is automatically changed to 300 kHz ... 3 GHz.Shouldn't it be set to the full range of 30 kHz - 6 GHz of my VNA?Next, i start a "S11 1-Port" calibration.When selecting "OPENS", a new menue appears and asks me for "OPEN (M)" or "OPEN (F)".Since i am using the female-open, i guess selecting "OPEN (F)" is correct here?The same applies to the SHORT.Just the "LOAD" does not open a sub-menue for (F) or (M).Ok, so after i finalize the calibration by pressing "DONE 1-PORT CAL", i set the VAN to Smith-chart to verify if calibration is correct.I do this by attaching the SHORT again and check if the Smith-chart gives me a point at the short-position.However, i don't get a dot at the short position but a line reaching from short to almost infinit on the upper, outer pure inductor circle.Similar, just mirrored is displayed when the OPEN reference is connected.For compensation, i applied a port extension of 58.14 ps and get the expected results (dots) with all 3 calibration standards.I thought that with the complete calibration data on the floppy disk, there would be no need for manual port extension entry?Or maybe i am doing something completely wrong here?ThanksP.S.:Another thing that irritates me is that the 50 Ohm references are 49,5 and 51,1 Ohm instead of "50,0".I would expect to get better quality references for that price?

author: orin
author_rank: Frequent Contributor
timestamp: March 19, 2018, 11:50:56 pm
content: Quote from: rfspezi on March 19, 2018, 08:06:25 pmNot usually for HP VNAs.The (M) means a male test port and (F) a female test port. So if you are using a female open, you should select OPEN (M) and if using a male open, select OPEN (F).(Later Agilent changed the convention to indicate the sex of the standard and replaced the parentheses with hyphens so OPEN -F- would indicate a female open and so on.)This information is on Dr Kirkby's web site, but I could only find it under the old NCV032B kit information here:http://www.kirkbymicrowave.co.uk/support/Kits/NCV032B/HP/

author: G0HZU
author_rank: Super Contributor
timestamp: March 20, 2018, 12:53:47 am
content: QuoteDon't forget that your cal kit SHORT and OPEN is at the far end of either a male-male SMA adaptor or a female SMA adaptor. The typical delay in the F-F adaptor is about 42ps and the M-M is probably about 58ps.So the moment you put your cal kit OPEN back on the VNA after a calibration the open end of your OPEN will be either 42ps or 58ps away from your reference plane. So the smith chart on the VNA will show a 0-6GHz line going maybe halfway around the smith chart. It's effectively measuring the SMA F-F barrel.My guess is that you have tried to do a 1 port calibration and told the VNA the wrong gender for the cal kit. So the 42ps and 58ps are muddled. Try again for the 42ps female OPEN (and don't forget the VNA refers to this as OPEN (M) ) and it might look like this:

author: G0HZU
author_rank: Super Contributor
timestamp: March 20, 2018, 01:09:13 am
content: If you put the female SHORT back on the VNA after a successful calibration it will probably look like the image below. These smith chart images for the female SHORT and OPEN are based on s1p data from another Kirkby cal kit. i.e. the SHORT will look like a short that is shifted about 42ps from your reference plane once you fit it back on the VNA after a calibration.

author: Bud
author_rank: Super Contributor
timestamp: March 20, 2018, 03:16:51 am
content: Quote from: rfspezi on March 19, 2018, 08:06:25 pmYou should not do this. Why? Think about what your VNA will show if you connect an ideal Short or ideal Open. They will Not be at zero and infinity dot position as they should, because you offset the chart by 58ps. Therfore any measurements you take with such port extension applied will be invalid.

author: TheSteve
author_rank: Unknown
timestamp: March 20, 2018, 06:09:27 am
content: Quote from: rfspezi on March 19, 2018, 08:06:25 pmOn my "out of spec" SMA kit my female load is 51.05 ohms and my male load is 49.25 ohms.And I do get the expected smith chart results G0HZU suggested you would.The kit cal info does have a max frequency entered into it that was supplied for my N9912A, I'm not familiar with the 8753ES but is it possible Dr Kirkby entered 3 GHz into your data for a max frequency instead of the spec'd 7 GHz or your 8753ES's 6 GHz.

author: rfspezi
author_rank: Regular Contributor
timestamp: March 20, 2018, 07:10:16 am
content: Quote from: G0HZU on March 20, 2018, 12:53:47 amThank you for the explanation!So I definately used the wrong sex and need to think at the reference plane.If i understood right, i should be able to verify a correctly performed calibration by e.g. connecting the SHORT-reference and applying a port extension that exaclty matches the one specified in the calibration data for convergence?Concerning the loads the calibration file says:Code:** Male load. **Minimum frequency: 0 MHzMaximum frequency: 7000 MHzOffset Zo: 50.0 ohmsOffset loss: 1000 Mohm/sOffset delay: 0 ps** Female load. **Minimum frequency: 0 MHzMaximum frequency: 7000 MHzOffset Zo: 50.0 ohmsOffset loss: 3000 Mohm/sOffset delay: 0 psShouldn't the resistor values match the truely measured ones? (although measured with DC)I guess the correct way would be to get better 50 Ohm references, right?

author: drkirkby
author_rank: Newbie
timestamp: June 10, 2018, 07:31:32 pm
content: Hi,I'm Dr. David Kirkby, the director of Kirkby Microwave.Since a few people asked, I can confirm that the attenuator supplied in the SMA kitshttp://www.kirkbymicrowave.co.uk/support/Kits/85033/is measured with an Agilent 85052B 3.5 mm cal kit,notthe SMA kit supplied. There are 5 measurements made on the SMA attenuator:S11S21S12 (in theory the same as S21)S22Reflection coefficient at the male port, with the female port unterminatedS11 and S22 measurements can't be expected to be very accurate at low frequencies, as the return loss of the attenuator is very good. A high return loss means a high measurement uncertainty. As the frequency rises, so the return loss of the attenuator deteriorates, and the S11 and S22 measurements are more meaningful. But the S21 measurement is useful at all frequencies.The measurement of a reflection coefficient at the male port with the female port unterminated gives a return loss that will be met in many practical circumstances.On the N kitshttp://www.kirkbymicrowave.co.uk/sales/85054/we also measure the reflection coefficient at the female port, with the male port unterminated. But we don't do that on the SMA kits as the nut on the male SMA wobbles around, changing the capacitance to the inner conductor. Since such a measurement is potentially unstable, we don't do it.There's no doubt the attenuator is not a perfect test of a VNA, but it has in the past highlighted problems when people have entered the coefficients incorrectly.There's a review of our kit on Amazon UK by Dr. Robert Watson at Bath University. He describes how he used airlines, and a Beatty Standard and compared the kit with various other kits. Seehttps://www.amazon.co.uk/Kirkby-Microwave-85033-calibration-verification/dp/B01BAWR70M/ref=sr_1_1?ie=UTF8&qid=1467301985&sr=8-1&keywords=85033+sma+calibration+kit/I have no connection with Robert Watson, other than he bought a couple of kits, and another UK university bought one when they were collaborating with him. I never studied at Bath University, and have never met him, but he has agreed if anyone has any questions, he may be contacted. You can find his details on the Bath University website.As for the comments by someone about the DC resistance of the loads, we are less concerned about their DC resistance than their RF performance. The loads are tested to have a return loss of at least 32 dB from 50 MHz to 7 GHz in a standard kit. (They are usually much better). We have an HP 3457A 6.5 digit multimeter (currently at Keysight for calibration), so could easily measure the DC resistance using 4-wire Kelvin connections. However, I feel that's irrelevant, as it does not indicate the RF performance at all, because the real part of the resistance isnotindependent of frequency. You will never see a specification for the DC resistance (other than 50 or 75 ohms) in any cal kit from Agilent. Of course, if the DC resistance is well away from 50 ohms, the return loss at low frequencies would be poor, and we would reject the load, irrespective of what its performance is like at microwave frequencies.On some loads, the return loss at 50 MHz (the lowest frequency we measure) will be worst than at 7 GHz. Whilst this is the exception, rather than the rule, it does indicate that the DC resistance is not so important.We do now provide measured S-parameters on the opens, shorts and loads so if one has a VNA that allows the S-parameters to be imported, that data could be used.Someone asked why when they loaded the floppy disk into an 8753, it indicated a maximum frequency of 3 GHz. That is because we find it quicker to create the files on our 8753ES, which is a 3 GHz unit. The actual coefficients are valid to 7 GHz, and a 6 GHz 8753 will calibrate up to 6 GHz. I have never seen one, but there's some information in one of the data sheets from Agilent that suggest there were versions of the 8753 up to 8.5 GHz. I guess these were "specials". If you did have such a unit, a standard SMA kit would not calibrate it beyond 7 GHz.We can do SMA kits up to 12 GHz now, but they are more expensive, as very few loads have suitable performance at 12 GHz.I strongly suggest if anyone does have any queries about how to use our kits, it is better to ask us, than ask on a forum like this. I see people asking if the SMA_M_M file is the right one to use in a particular circumstance.Oh, and one more thing. The Agilent N9912A FieldFox is a very poor VNA. If you ask Agilent, they will tell you it is only designed for basic measurement. It can not even measure the phase of S21 - only the magnitude. When I first played with an N9912A I thought there was a fault on it, as the dynamic range is only about 50 dB. I'm told that is normal. The N9912A really is a brain-dead instrument.Dr. David Kirkby,Kirkby Microwave.

author: drkirkby
author_rank: Newbie
timestamp: June 10, 2018, 07:42:35 pm
content: Quote from: Safar on February 18, 2018, 02:31:08 pmNote those words are a direct copy from the Kirkby Microwave auctions!They did not copy the link to our website! The Chinese have just copied what we wrote. I did think of complaining to eBay, but decided not to bother.Dr. David Kirkby.

author: drkirkby
author_rank: Newbie
timestamp: June 10, 2018, 08:07:15 pm
content: Quote from: rfspezi on March 19, 2018, 08:06:25 pmIf you need advice, you should contact us!The reason the span is set from 300 kHz to 3 GHz on your 6 GHz 8753ES is that we actually create the files to go on the floppy disk using an 3 GHz 8753ES, which works from 300 kHz to 3 GHz. This is less tedious, and less error prone than trying to use any Agilent software, like the Cal Kit Manager 2.1 software. The coefficients are valid to 7 GHz though. If you load the SMA kit, and look at the frequency range of any of the standards, you will find the minimum frequency is 0 GHz and the maximum 7 GHz.Someone else has already pointed out some other errors you made, so I will not repeat them, but I thought I'd explain why you see a span of 300 kHz to 3 GHz. You will just need to set the start and stop frequencies to what you want.Dr. David Kirkby.

author: TheSteve
author_rank: Unknown
timestamp: June 13, 2018, 04:47:38 am
content: It is great to have you here David.I have been playing with more VNA's. I have something that is full 2 port now to 6 GHz. With a full 2 port OSLT cal my Mini Circuits VAT10+ looks quite reasonable when compared to the datasheet. Much better then the results my N9912A was providing.

author: sixtimesseven
author_rank: Frequent Contributor
timestamp: July 17, 2018, 10:52:41 am
content: Sorry for hacking this thread, but what do you guys think about the possible cal kit options for a HP3577A with S-Parameter test set (100khz-200Mhz, 50Ohms)?The Kirkby Kit with 7GHz seems to be overkill for me at the momentThanks

author: TheSteve
author_rank: Unknown
timestamp: July 17, 2018, 04:31:12 pm
content: DIY is totally possible but he will still need someone to measure them for him.

author: drkirkby
author_rank: Newbie
timestamp: July 23, 2018, 11:19:16 am
content: Quote from: rfspezi on March 19, 2018, 08:06:25 pmIf you need advice on the use of our kit, please contact us, but I will answer them best I can here.Quote from: rfspezi on March 19, 2018, 08:06:25 pmI put the answer why your VNA is set from 300 kHz to 3 GHz in our FAQ.https://www.kirkbymicrowave.co.uk/Support/FAQ/Quick-questions-about-vector-network-analyzers/#Frequency-is-3-GHz-on-6-GHz-VNAThe short answer is we write the coefficients using a 3 GHz 8753ES. The calibration standards arenotmeasured on the 3 GHz VNA, but using the 3 GHz 8753ES it is just a convenient way for us to write the floppy disks. The standards are measured on a 20 GHz VNA (8720D) with a 26.5 GHz calibration kit (85052B).As for the correct file to load (SMA, SMA_F_F or SMA_M_M), it does not matter for 1-port calibrations. For 2-port calibrations it does, as the different files each have a different delay on the thru standard. An explanation is athttps://www.kirkbymicrowave.co.uk/Support/FAQ/What-file-should-I-load-from-the-floppy-disk-into-the-VNA/Quote from: rfspezi on March 19, 2018, 08:06:25 pmA low frequency (DC) resistance of 49.5 ohms, the VSWR is 50/49/5=1.0101 (return loss 46.0 dB), which is no worst than the return loss of the loads in the Keysight 85052B (US$ 12,956 in July 2018) 3.5 mm calibration kit. A DC resistance 49.5 ohms would not be out of specification in that kit.Now 51.1 ohms is a VSWR of 51.1/50 = 1.022 (return loss 39.3 dB), which is within the specification of our kit (> 32 dB return loss to 7 GHz), but not the 85052B, but then our kits do not cost almost $13,000. (For the 8, 10 and 12 GHz version of the SMA kit, the return loss of the loads will be at least 32 dB at 8, 10 or 12 GHz respectively)What we care about is theRF performanceof the kit. If the loads were made from wirewound resistors, as standard resistors usually are, the DC resistance could be made very close to 50 ohms, but the RF performance would be appalling.You might note there's no specification for the DC resistance of RF terminations in any of the Keysight calibration kits, nor in the loads from companies like Minicircuits. It really is irrelevant.We have a HP 3457A 6.5 digit multi-meter here, which we had calibrated by Keysight only a month or two ago. It supports 4-wire resistance measurements. We could easily measure the DC resistance of the loads, but tests performed in the past indicate there's no correlation between DC resistance and microwave performance. So worrying about DC resistance is pointless. Loads are screened based on their RF performance, not the DC resistance.Dr. David KirkbyKirkby Microwave Ltd.

author: G0HZU
author_rank: Super Contributor
timestamp: July 23, 2018, 10:30:44 pm
content: QuoteHmm... I think you are trying to justify your use of a low cost wideband SMA 50R 'termination' here rather than the type of precision 50R load found in an expensive commercial RF cal kit. I don't 'test' HP/Agilent/Keysight cal kits very often but usually the performance/agreement between our kits at work (at LF) is excellent and this implies the LF resistance must be very close to 50R.When I made my homebrew SMA cal kit many years ago I tried to get as close to 50R on a DMM (at DC) as possible so spent some time selecting the best resistors to use. This cal kit always gives extremely good agreement at LF with a proper cal kit from Agilent so I think all the works Agilent/Keysight kits (and my homebrew kit) are very close to 50R at LF (eg at test frequencies <10MHz). I'd like to think they are all within about 0.1 to 0.2R of 50R at LF but I've never tried this test to prove it. I also have a Suhner (18GHz) SMA load here that I selected from a batch to be the closest to 50R (on a DMM) I could find. I sometimes use this instead of my homebrew SMA load.At work I think we have about a dozen 85033E 3.5mm kits and various 13-26GHz Ecal modules and a couple of 85032F N kits. However, I haven't tested all of them for LF performance. I have checked a few of them though...So a cal kit load that measures 51.1R at LF is an 'unusual case' in my experience.The Ecal kits will be corrected in a lookup table to be very close to 50R at LF although the only Ecal module I've tested extensively is my own one here at home. It usually agrees within a few tens of milliohms of 50R at LF compared to my homebrew cal kit and the hand selected Suhner 18GHz SMA load. The Suhner load and my homebrew SMA load have been tested in the past against an 85033E cal kit and I got similar agreement. So I generally take it for granted that a commercial cal kit will be very close to 50R at LF even though this isn't quoted in the datasheet.

author: G0HZU
author_rank: Super Contributor
timestamp: July 23, 2018, 11:05:34 pm
content: Here's an old plot of my Suhner 18GHz SMA load showing the LF performance. This load was hand selected from a large batch of identical Suhner 18GHz loads to be the closest to 50R and I just measured it again this evening (after many years) and it is 49.99R at DC on a Keithley 2000 4W meter.This plot was taken at work (a few years ago) using an 85033E cal kit and the VNA was a 6GHz 8753ES. It shows very close agreement with 50R all the way up to 200MHz. So this implies the 8753ES/85033E can measure a real 50R quite accurately.On my VNA here at home (using my N4431B-60006 Ecal to calibrate the VNA) the same Suhner 18GHz load measures 49.94R at LF. So pretty close to 50R again!I also dug out another Suhner 18GHz load and it measured 49.87R on the VNA (with the same Ecal calibration) across about 2-10MHz. On the 4W Keithley this second Suhner load measured 49.89R at DC. So good agreement again I think.

author: G0HZU
author_rank: Super Contributor
timestamp: July 24, 2018, 05:55:14 pm
content: FWIW at work today I tried measuring a number of 50R loads from our Agilent N and 3.5mm cal kits. I used a decent Agilent 4 wire bench DMM (calibrated at Agilent in April this year) and the 'worst' load I found in the group test measured 49.97 ohm at DC. The rest were slightly better than this but all very close to 50 ohms as expected.I also tried calibrating an E5071 VNA with one kit and measuring the resistance of the other Agilent cal kit loads at low frequencies. They all measured within a few tens of milliohms of 50.00 ohm at a few MHz and some were within just a few milliohms of the reference load used for the VNA calibration. Some of our Agilent cal kits must be >15years old so this is a good result I think.

author: hendorog
author_rank: Super Contributor
timestamp: July 24, 2018, 08:01:07 pm
content: Quote from: G0HZU on July 23, 2018, 11:05:34 pmThis is what I did too when I got my 8753 up and running so I'm glad to hear it makes some sense.In addition I entered the measured resistance into the VNA cal standard table, instead of just 'Load'.IIRC that helped the VNA measure the other loads more precisely.Interestingly the SDR Kits guys use this DC measurement to characterise their loads in their low cost cal kits - you get a little label in the box with the result hand written on it.Of course this doesn't necessarily mean that it will still be 50 ohms at 6GHz, which is I think what Dr Kirkby was saying.

author: G0HZU
author_rank: Super Contributor
timestamp: July 24, 2018, 10:15:31 pm
content: I think you also have to correct for the time delay in the SMA load I'm not sure how muddy things get if you were to try and do some precision work with a full 2 port VNA with an uncorrected 51.1R SMA load as the calibration reference. I wouldn't want to use it like that even if it would be OK for many casual tasks. I'm not sure I want to waste the time working out how much it will degrade certain types of measurement. I'd rather source a decent load and keep it simple

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 25, 2018, 03:19:16 am
content: Quote from: hendorog on July 24, 2018, 08:01:07 pmwhat i suspect he's saying is, albeit the inaccuracy of the load at DC and to some extend at RF, the error should be close to insignificant (for normal Joe's purposes).. but to know exactly, one has to make a comparison test requiring both the inaccurate load and super accurate $$$ load in hand, calibrate VNA with both and make few practical measurements to see how the measurements will be far off. i cant do the test since i cant justifiably afford $2,000 and beyond calibration kit let alone $13,000. so i have to anticipate more ripply measurement than it should. my 2cnts.

author: Bud
author_rank: Super Contributor
timestamp: July 25, 2018, 04:23:05 am
content: You do not have to do that elaborate test, and it will not be conclusive anyways because the best commercial calibration loads still have errors. All you need is to know your calibration load's Retun Loss within the frequency range of interest, then you can reference existing charts / tables that show +/- error of measurements for a given Return Loss figure. You can pull these charts from the Internet.Now the problem is to know your cal load RL, that you need to measure against a decent calibration kit on a VNA or from the manufacturer data.

author: hendorog
author_rank: Super Contributor
timestamp: July 25, 2018, 05:06:21 am
content: Quote from: G0HZU on July 24, 2018, 10:15:31 pmYes - but consider the inverse case, which is what I was trying to do:Can you make your measurements _more_ accurate by entering the exact resistance of the load?I believe that the assumption that a load is exactly 50 ohms is a bit of an historical relic.So taking the argument one step further, why not do away with the model altogether? Since a better model of the load is an S-param measurement of the load, then we could just use that instead and calibrate on the PC.

author: G0HZU
author_rank: Super Contributor
timestamp: July 25, 2018, 10:42:15 pm
content: QuoteI guess so, assuming the VNA supports this feature. However, I'm not sure how it handles both the resistance and the Zo of the delay in the standard. It just seems to me to be a bad idea to have to resort to this. Pretty much all of my VNA experience is with official cal kits or my own homemade ones and they are probably all within 0.05R of 50R at LF so I don't have much experience of fudging the 50R standard.I chimed in because DrKirkby seemed to imply (to his customer) that the DC/LF resistance is irrelevant and can be ignored in the cal kit file. But I think the real/imaginary parts of the load at lower frequencies needs to be very close to a pure/accurate 50R resistor if you want to exploit the potential of a decent VNA when measuring impedance or if making a decent 2 port model at these lower frequencies. In my experience. a good VNA and a decent cal kit can deliver really good accuracy for impedances in the 5R to 2000R range at low frequencies. Much better than the uncertainty stats given for a default VNA with fairly grim uncertainty factors for the various contributors to overall uncertainty.An uncorrected 51.1R resistor would give an additional error of over 2% for this when measuring typical LCR parts at low frequencies. I think the error will be worse for some types of measurement. Also, even a decent VNA will typically struggle a bit when measuring the Q of inductors on the HF bands but in my experience the results can be quite good with a good VNA and cal kit as long as the Q is in the order of 50-100 and the inductance is in a typical/sensible range. I'd expect an uncorrected 51.1R load to magnify the uncertainty of a Q measurement quite a bit.Up at microwave frequencies the impact is going to be less but down at a few MHz to maybe 100MHz I think a VNA can deliver really good performance as long as the 50R load has a decent reflection coefficient down at these frequencies.QuoteAgreed, but based on the physics of the component I'd expect the return loss of a decent 50R cal kit load to be in the ballpark of 70dB at a few MHz. Even a cheapo homebrew load made from selected chip resistors will be close to this at a few MHz if selected to have a load resistance very close to 50.00R at LF. Obviously, this would have to be verified as you say, but I don't think it's rocket science to make a reasonable 50R SMA load.A couple of years ago I posted up a measurement of my homebrew SMA load. It was quite a few years old by then and quite worn but it still managed 40dB return loss by 3GHz and the LF resistance was within maybe 20 milliohms of 50R. This was made using a pair of hand selected 100R chip resistors mounted on a decent quality SMA PCB end launcher. I chose resistors and an end launcher type that gave very good results across this range of LF through 3GHz.The plot below of my homebrew load was taken with an ENA VNA calibrated by a decent 13GHz Ecal module. It isn't quite this good today because it has been used a lot in the last two years and is showing increasing signs of wear.

author: G0HZU
author_rank: Super Contributor
timestamp: July 25, 2018, 10:58:57 pm
content: In terms of a typical application for that old homebrew load I used it as part of my homebrew cal kit to design and verify a precision (SMA connector based) resistive splitter a few years ago. This was needed to help me service an ancient HP8405A vector voltmeter and verify the performance.I used the cal kit to check out various SMD chip resistors (when piggybacked) to make up the resistors in the splitter. I wanted to match the performance of a decent commercial splitter up to the 1GHz range of the HP8405A. I needed ultra low port VSWR and sub 1degree phase balance and very good amplitude tracking on both arms of the splitter. To get this I needed resistances in each arm that were very close to 50.00R across LF to as close as 1GHz as possible. So I needed a decent cal kit for this.I used my old/lowly HP8714B VNA and the homebrew cal kit to do all this because that is all I had back then. When I got the 4 port ENA VNA and the 4 port Ecal module I remeasured it formally as a 3 port device (to 3GHz!) and you can see the results below.It was very impressive indeed for port VSWR, phase tracking and amplitude tracking across LF to 1GHz as you can see in the plots below. It degrades a bit by 3GHz but is still about as good as a typical commercial precision splitter up to 1GHz

author: hendorog
author_rank: Super Contributor
timestamp: July 25, 2018, 11:17:51 pm
content: Quote from: G0HZU on July 25, 2018, 10:58:57 pmThat is impressive - I made a splitter as well but as I recall it is not even close to that performance.As a matter of interest, what does your eCal measure itself as? I am curious how close that is performance wise to a physical cal kit.

author: G0HZU
author_rank: Super Contributor
timestamp: July 25, 2018, 11:36:58 pm
content: QuoteThanks. A fair bit of design effort went into it and it would have been far more sensible to just buy a splitterI used the homebrew cal kit, the HP8714B VNA and a suitable test fixture to measure the best resistor type to help me reverse engineer a decent model of the chosen chip resistor. I then designed and simulated a (0.02" Rogers 4003C) circuit board using Genesys and Sonnet EM with my resistor models to try and get the lowest port VSWR across at least 1GHz. I used a precision PCB mill with decent end mill tools to make the PCB I had a good result with the very first PCB design and I think there was an element of luck in the phase matching. I didn't expect it to be that good and I only needed a few scrapes with a scalpel in the right places on the PCB to get the phase that flat. This was taken with the SMA connectors done up with a torque spanner as the phase shifts with connector tightness in the GHz region as you would expect.I'm not sure it's possible for me to directly measure the load in the Ecal because it is all controlled by the VNA via USB. I think the Ecal is at its very best above a few hundred MHz. By that I mean probably better than a typical 85033E mechanical kit. Below this (especially down at a few MHz) I think the mechanical kits (and my homebrew kit) are marginally better for both 1 port and 2 port measurements. But that is based on my experience of using all three.When I designed my SMA cal kit I went to similar (nerdy) lengths to verify I had the delays and corrections in my user cal kit as close as possible. I developed various passive 2 port test fixtures here that can easily show even slight errors in the cal kit's user file when the VNA test fixture s2p data is post processed on a computer. This work really highlighted to me why the 85033E cal kits and the Ecal modules are so expensive and I'm impressed how consistent all our 85033E cal kits are at work.

author: Andrey_irk
author_rank: Regular Contributor
timestamp: July 30, 2018, 08:17:49 am
content: G0HZU,If you are concerned about the RL accuracy when measuring low RL values then you should look at the residual directivity value. These are in order of 40-50dB for the most of commercial kits. Keysight, for instance, provide these values for every VNA calibrated with every their kit or ECal (as long as I remmember).51.1 Ohms gives you these 40dB of RL at low frequencies and the high frequency values will depend on the parasitics (which are usually much more difficult to make small). And it won't help you if you get a 49.999Ohm resistor as the HF performance won't be affected.If you measure say 20dB RL DUT with with a VNA calibrated to have 40dB of directivity - it will give you an error of about 0.8-0.9dB, which is pretty good.At work I have an SMP cal kit, which has a Load standard with (according to specs) 50+-0.25Ohms, but only 25dB RL beyond 4 GHz. And I'm not aware of any commercial kits with better specs for this type of connectors. So, with our 20dB RL device this kit gives us an error of 4-7dB (!).P.S. I'm not a guru at this, so hope Dr. Kirkby will correct me if I'm wrong.P.P.S. Is it possible to invite Joel Dunsmore here?

author: G0HZU
author_rank: Super Contributor
timestamp: July 30, 2018, 02:12:03 pm
content: I think you are missing the point I'm trying to make. DrKirkby said the resistance at LF is irrelevant.Suppose I wanted to test some 100R resistors across temperature to see how accurate and consistent the resistance was over maybe 0-200MHz.If I take DrKirkby's advice then it won't matter which Kirkby cal kit I use to measure the complex impedance as long as they all have the same 39dB return loss. So for each test at each temperature I could select a Kirkby cal kit at random (from a box of several) to use and not care if the real part of the calibration load was 48.9R or 51.1R between the kits.But I'd see errors of > +/-2% for the real part of the impedance even for this simple test at a fixed temperature. I could correct the resistance in the user file for each cal kit to minimise the error but DrKirkby implies all this is irrelevant.

author: Bud
author_rank: Super Contributor
timestamp: July 30, 2018, 03:30:42 pm
content: Can't you enter the reference impedance value in the VNA settings and call it a day. Not all VNAs may have that setting changeable though.

author: G0HZU
author_rank: Super Contributor
timestamp: July 30, 2018, 03:42:48 pm
content: I guess so but I don't know if a VNA would interpret this as a 51.1R resistor with a 50R Zo delay or as a 51.1R resistor with a 51.1R delay.So it might cause subtle problems when being used up at higher frequencies. I had a rummage at work to try and find an SMA 50R termination as poor as 51.1R at LF but couldn't find one. The other option is to use a homebrew SMA load up to a couple of GHz that is selected to give close to 50R and then use the wideband 51.1R load up at higher frequencies if critical measurements are being done in either case.

author: Bud
author_rank: Super Contributor
timestamp: July 30, 2018, 04:17:24 pm
content: VNAs should not assume things, unless it is a Chinese one where anything is possible. I'd think the math certainly has delay variable in it but any delays should be specified by the user explicitly.

author: Andrey_irk
author_rank: Regular Contributor
timestamp: July 31, 2018, 01:33:09 am
content: G0HZU,Ah, now I see what you mean.Quote from: G0HZU on July 30, 2018, 03:42:48 pmI think if you leave the load connected after calibration and take a look at the smith chart you'll see how it interprets the 51.1R load. Anyway, in E5071? for instance? you can set offet Zo, impedance value and even offset loss. Although if you want to specify load impedance that is not 50R, then it will be a different standard - arbitary impedance. And I don't know if there are any limitations with using this kind of standards instead of usual loads.

author: Andrey_irk
author_rank: Regular Contributor
timestamp: July 31, 2018, 01:40:20 am
content: Still, I understand that it is not difficult to measure LF impedance, but I don't know if it'll give a real benefit. Maybe Dr. Kirkby calculated all the errors and realized that it really doesn't worth it (to some extend of course). Maybe the noise floor is much higher.

author: mark03
author_rank: Frequent Contributor
timestamp: June 10, 2019, 01:09:53 am
content: Quote from: Bud on July 30, 2018, 03:30:42 pmYes, at least on my VNA (Agilent 4396B) the "arbitrary impedance" standard type has the usual offset parameters (delay, loss, Z0), then a separate termination impedance.I found this necessary to accurately model my own DIY set of female SMA standards. The professional cal kit I borrowed (a Copper Mountain S911) is spec'ed at better than 38 dB return loss from DC to 9 GHz. The [measured by me] DC resistance is 50.8 ohms, which is still in spec, but makes LF measurements less accurate than they ought to be. I couldn't figure out why my DIY load was measuring at ~ 49.2 ohms on the VNA, all the way down to 1 MHz, when I had measured its DC resistance at 50.0 ohms on my DMMI guess the moral of the story is that some cal kits (not just Kirkby) are really focused on microwave performance where 40 dB return loss is pretty good, and it's mostly weirdos like ham-radio people who care about LF accuracy, so if you are one of those people it's worth measuring the DC resistance and using that up to ~100 (?) MHz. Unless you have access to higher-end kits like G0HZU

author: Noy
author_rank: Frequent Contributor
timestamp: November 13, 2020, 10:38:32 am
content: Hi, is the suggested :https://www.sdr-kits.net/index.php?route=product/product&path=66_68_69&product_id=50Kit useable for up to 3.2GHz im thinking abaout buying / hacking a SSA3021X-Plus but additional >>100€ for a calkit is said, the SSA is expensive enough for me..?

author: Noy
author_rank: Frequent Contributor
timestamp: November 13, 2020, 12:28:08 pm
content: SSA3021X-Plus is hackable up to SVA1032XThan it is a VNA.

author: tautech
author_rank: Super Contributor
timestamp: November 13, 2020, 06:42:50 pm
content: Quote from: Noy on November 13, 2020, 10:38:32 amLikely to be quite good enough for most measurements.Doing a Cal with other than kits listed in the Cal menu you need save the file to the SVA file system and then apply it as a Correction.All simple enough once you get your head around the process/method.Looking forward to seeing your measurements.

author: Noy
author_rank: Frequent Contributor
timestamp: November 13, 2020, 08:36:06 pm
content: Is there a list which "official" calkits are supported from the cal menu?Sometimes i think tautech is an inoffical siglent fae crew account (multiple fae behind this account..) or maybe a very smart siglent bot / KI.. :-D so many posts in so many threads where do you work beside posting ? :-D

author: tautech
author_rank: Super Contributor
timestamp: November 14, 2020, 01:38:45 am
content: Quote from: Noy on November 13, 2020, 08:36:06 pmThe Siglent Cal kits of course are all supported plus the crossover ones listed in this document:https://siglentna.com/wp-content/uploads/2020/08/Mechanical-Calibration-Kit-Datasheet.pdf

author: hendorog
author_rank: Super Contributor
timestamp: November 14, 2020, 08:18:30 pm
content: Quote from: Noy on November 13, 2020, 08:36:06 pmHe's definitely a bot. But a fully mechanical one. IC's weren't invented when he was built.The Tauturk.

author: Noy
author_rank: Frequent Contributor
timestamp: November 18, 2020, 10:35:57 pm
content: Is it worth to pay the "extra" for the SDR Kits Calkit (box, load measurment, male male Adapter) instead of buying the parts as "single" from Mouser?Refering to:http://www.hhft.de/index.php?page=competences&subpage=calibrationMouser: 56€ + 16% vat inkl. shippingSDR Kit : 75€ inkl. Vat + shipping (85€ total)I think same parts and i think the only measured thing from SDR kits is resistive load resistor..I can do this also with 4 wire measurment with my fluke8840a or?Or are there more measurment done by them?Male - male Adapter is sure also available from Mouser (didnt searched , not sure if i need this one...)Suggestions??

author: tautech
author_rank: Super Contributor
timestamp: November 19, 2020, 07:29:46 am
content: Quote from: Noy on November 18, 2020, 10:35:57 pmSOL are the minimum you need and some kits also come with a through but they are all rated to a max frequency and when swept to that frequency there must be little change across the full range.You can sorta cobble a set together but good results are tricky to achieve as I found out trying to make some on the cheap for myself.In the end I sucked it up and bought a $400 SMA Cal kit.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 19, 2020, 07:31:18 am
content: Quote from: Noy on November 18, 2020, 10:35:57 pmwell without providing CAL kit coefficients or s1p profiles, there is not such thing as even "Kirkby alternative", you can buy whatever cal kit you want and be happy about it, you can even make your own its doesnt matter. you can do the "inverse" or "reverse" profiling from whatever s1p/s2p plot from your VNA. if you care about Load quality that we all can measure with any DMM, you can get from already mentioned brand such as Rosenberger or whatever name they are you can browse the thread. or better, buy few Loads and hand pick which one is the closest to absolute "Fifty Ohms" and still cheaper compared to any knock off or "Kirkby alternative" buzzed/advertised as "CAL kit" out there (you can already have few terminations to test things such as 2/3/4/5 50 ohm signal splitter etc you are going to need it today or 10 years from now). you may get cheaper than your mentioned Mouser or SDR-kit's CAL kit at $50 and get a free (NanoVNA V2+ with decent quality 50ohm Zo SMA pigtail cables) if you buy from Tindie... or$4 thisjust look closely from the link you gave about these facts...Quotethis is what we call... Ideal Calibration Standard, even HP $20K CAL kit cant achieve this in reality. offset length can be measured physically with caliper, one eye closed and tongue at the right angle. electrical one way trip can be observed from VNA plot/TDR and punch the figure into the formula to get dielectric constant and hence "electrical length" aka "offset length". the deal here is to get 3rd degree polynomial approximation for those Cn and Ln up to whatever BW you are interested in, maybe those are negligible up to say 3-6GHz? i dont know. if someone can figure that out from "reverse" characterization from even a cheap VNA like NanoVNA alone, there is no reason to buy from Kirkby or HP at all, they should not be even mentioned in the first place, and there should not be any comparison to or no such thing as "Kirkby alternative" at all... $4 CAL kit is what we should look after if we dont care about polynomials, ymmv. cheers.

author: Noy
author_rank: Frequent Contributor
timestamp: November 19, 2020, 08:04:20 am
content: There are more informations available:https://www.sdr-kits.net/documents/Rosenberger_Female_Cal_Standards_rev5.pdfSo because they are "standard" Rosenberger types i think these informations are also true for the "single buy" mouser parts.SDR-Kits are using the same parts like stated on the website. But I#m unsure if SDR-Kits are measuring anything "more" than the 50 Ohm impedance and write this value on top of the box...If this is all there is no need to pay the "extra" if its only a small wood box...This is what i mean. I think rosenberger parts are way more "true" even with this provided sheet against these cheap china parts (i already have delock 12GHz N->SMA Adapters, some decent SS405 2x (20cm) / 2x RG405 (1m) and some (10x 20cm / 2x 1m) RG316 cables for up to 3.2GHz (hopefully) also RG58 with bnc but these are <<1GHz useabel..) And all kind of "cheaper" SMA adaptors. Only a calkit with "stated true" things is missing (beside the china stuff) but 400$ if the whole VNA was only 1600€ is for hobby use a bit too much. So the rosenberger parts are (i think for hobby use) best bang/buck? And since i will not go higher than the 3.2GHz i think its sufficiant?But I'm new to this stuff so i will need an advice.

author: tautech
author_rank: Super Contributor
timestamp: November 19, 2020, 08:14:00 am
content: Quote from: Noy on November 19, 2020, 08:04:20 amSee what they're really like when you sweep them.I played around with a SMA load member hendorog gave me which he said measured quite reasonable with his HPAK and SH VNA's and it was pretty good on my SVA1032X however his Kirkby Cal kit was somewhat better.IIRC I've posted some sweeps in the SVA thread, go have a peep.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 19, 2020, 08:34:39 am
content: afaik, they can only gather research on nice appearance "butt plug" for open or short etc and save your time from calculating offset (mean) length and collect/put them in a nice wooden box and possibly do the "comparative/relative" quality check to their more pricey CAL Std (you can ask them what, i dont know). those are worth the price increase if you can appreciate that. but the cost for characterization is another thing. individual/unique coefficients/character profile files for your kit and getting a nice calibrated equipments (aka expensive) to get a reasonable transferable standard worth that another cost.Quote from: tautech on November 19, 2020, 08:14:00 amcompared to what? i can make a sloppy diy cal kit and make them flat to 6GHz on a VNA with zero offset everythings. one clue though to see a good LOAD without relative comparison is its return loss, but its real impedance and esp for OPEN and SHORT... you can be happy about anything.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 19, 2020, 10:38:59 am
content: Quote from: Noy on November 19, 2020, 08:04:20 ami just noticed they use Thru as Open, to cut corner maybe? thats funny, as i read somewhere, the Open need to be shielded to reduce nasty/random "fringing capacitance" effect. you can download plenty of "Basics of VNA" and "Calibration Standard" materials esp good materials/appnotes from HP/Keysight and learn as you go, i'm also still learning, there are lots of things and maths to learn in this arena.

author: Noy
author_rank: Frequent Contributor
timestamp: November 19, 2020, 10:52:07 am
content: So basically put a cheap china "open" on the other side of "thru" to close the shield?

author: switchabl
author_rank: Frequent Contributor
timestamp: November 19, 2020, 11:37:09 am
content: So a lot of things to unpick here:- The kit from SDR kits is really just the normal Rosenberger parts with a box and a 4-wire resistance measurement. I seem to recall that the price on Mouser was around the same, but if you can get them cheaper elsewhere now, no reason to pay more.- The offset lengths given by HHFT and Kurt Poulsen contain the first capacitance/inductance term (C0/L0), which really just gives a delay. You cannot derive them from a mechanical measurement. You also cannot measure them on a VNA without calibrating it first against known standards.- I have seen some measurements on a lab-grade VNA of the open and short and they didn't look bad to 5GHz+. The measurements shown on the HHFT page are probably not a bad indication of what to expect. On the plots they show, the performance >3GHz seems to be limited mostly by the load.- The mechanical dimensions of the parts are probably quite precise, but the properties of the PTFE dielectric will vary from batch to batch. So if you need a more accurate characterization (with higher-order capacitance terms), you would really need to measure each one individually (like Kirkby does). Or use 3.5mm parts with air-dielectric (like Keysight, Spinner, Maury Microwave or the proper Rosenberger cal-kits). Those are very consistent and the RF properties can essentially be calculated from the CAD model.- I would recommend against putting a male cap on the female thru used for open calibration. The fringing capacitance is already factored into the offset delay and is likely to increase (slightly) with a cap. The point of shielding the open is mainly to prevent radiative loss, but even on a male SMA (which essentially has a tiny antenna if left open), this isn't really an issue until at least 5-6GHz.- The load has a relatively large tolerance (all of those cheap general purpose loads have). It is only guaranteed to have >26.4dB return loss above 2GHz. In reality, most will be a lot better than that but don't rely on it. At low frequencies, the main contribution is the tolerance of the resistive film, so selecting by DC resistance is not a bad start if you have several. Entering the DC resistance as a parameter is usually also better than not (at least to 2-3GHz), but keep in mind there is also a short piece of transmission line between the connector and the resistive film, so changes in the resistance don't translate into a purely real impedance change at higher frequencies. If you buy separately, any 12-18GHz female load from Minicircuits, Huber+Suhner, Telegärtner etc will be very similar, in case you can find some of those cheaper.- Buying a pack of cheap random loads on eBay and selecting those by DC resistance may end in disappointment. Some of those have really poor RF properties and even if you find one with 50.00Ohms at DC, it may be way off at a couple hundred MHz, let alone a couple of GHz. Buying cheap RF parts of unknown providence is risky business in general. Mechanical tolerances may be off and it's easy to damage a good connector by mating it with a bad one. So inspect carefully, keep questionable parts separately and don't connect them to expensive instruments/parts. Use some sacrificial adapters or cables in between.Never use male SMA connectors where you cannot rotate the barrel separately from the center pin (like in some cheap "calkits"). That is a sure way to eventually ruin the mating female connector.Overall, if you are looking for something cheap for non-critical measurements, the Rosenberger kit is probably your best option. It will not give you the confidence and accuracy of a proper calkit, but you get quality parts (mechanically) and to 2-3GHz performance will likely be respectable. It is also a female kit, which is likely the more useful one if you are getting just one. I don't know why all the cheap NanoVNAs all come with male ones.I am a bit more sceptical about their male kit. Like I said above, the male open cap doesn't really do much at low frequencies anyway, so the open measurement will depend more on your test connector than on the calkit.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 19, 2020, 12:21:05 pm
content: Quote from: Noy on November 19, 2020, 10:52:07 amas i said it does not matter actually if we dont care about polynomials. but my thought is, if they want to sell a nice cal kit set, why they let us to go to trouble to buy separate shielded Open? maybe it will cost them only extra $1.Quote from: switchabl on November 19, 2020, 11:37:09 amexactly my point in some of my earlier posts in the other threads too. but well, its not like the end of the world if we dont have a characterized CAL kit, it will not prohibit us from happy go learning. later i will look into how good a VNA can de-embed fixtures such as pcb, say if we want to probe at the very tip of smd components pad, i've been doing this for sometime by omitting cal parm and offsets, ie leave them all to 0, i will evaluate if my method is correct or what.Quote from: switchabl on November 19, 2020, 11:37:09 amyes agreed. this one point that i didnt highlight but it can be a concern if you try to mate with expensive equipment or cable. so from this point of view, NanoVNA's short and the $4 kit i linked are bad. but since my KC901V is using cheap sacrificial N-sma, and NanoVNA is using equally cheap female sma connector, this is not really an issue imho, and i usually use cables that are male connectors, so they wont mate with those solid Short male directly, a thru will become sacrificial.Quote from: switchabl on November 19, 2020, 11:37:09 amagreed too as this is what i found out with a couple of Loads/terminators i bought from china (not meant for CAL kit). but to know this, you need a good CAL kit in the first place.Quote from: switchabl on November 19, 2020, 11:37:09 ambecause the Nano has female input? or they figured it is better (more configurable) and they dont have to provide M-M thru. male cal kit can always be connected to F-F thru to get female version. i find F-F thru is inevitable and i very seldomly reach for M-M thru version.

author: Noy
author_rank: Frequent Contributor
timestamp: November 19, 2020, 12:48:29 pm
content: Quote from: switchabl on November 19, 2020, 11:37:09 ambecause the Nano has female input? or they figured it is better (more configurable) and they dont have to provide M-M thru. male cal kit can always be connected to F-F thru to get female version. i find F-F thru is inevitable and i very seldomly reach for M-M thru version.Sure, but normally i thought you will also calibrate your used cables out or not ??A decent / cheap "Calkit" for < 4-6 Ghz would be nice. All the expensive calkits are already up to >>10GHz which is not needed for "cheap" VNAs like siglent ones which are only up to 3.2GHz. Why aren't there affordable ones for less than <150€ with measured values?

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 19, 2020, 01:08:47 pm
content: Quote from: Noy on November 19, 2020, 12:48:29 pmKirkby SMA kits thats advertised as 6GHz are specified to 12GHz using 20GHz calibrated HP VNA, dont ask the CAL kit he uses as The Reference. to convincingly rate a kit to 3GHz, you may want to specify to like what? 4-6GHz? using calibrated reputable brand VNA like HP/Agilent/Keysight, that is still expensive investment, dont ever call them to quote for the CAL kit alone we'll come back in shame, to get the idea, check on used (out of spec) market in ebay. if target customers are hobbiests, its sad hobbiest always aim for cheap price (me included), making this unpleasant business to venture. going to companies and universities, they will tend to go beyond 10GHz with todays 5G age. so you could end up with an expensive piece of paperweight on your desk without return profit. among all, most of Kirkby's customers are universities and professors thats impressed by him. we dont go into the know-how knowledge yet for the reliable calibration/verification process. inside the usb drive of CAL kit profiles, Kirkby included bunches of app notes relating to his work (i guess free non copyrighted) materials mostly from HP, i think i've only read one or two of the materials.

author: switchabl
author_rank: Frequent Contributor
timestamp: November 19, 2020, 01:13:48 pm
content: Quote from: Mechatrommer on November 19, 2020, 12:21:05 pmBecause it makes very little difference and if it does, it will likely make the performance slightly worse. Shielding an open standard does not help against fringing capacitance, it introduces more of it. If you think about it, the dust cap is essentially one plate of a capacitor. The same is true with these cheap male "calkits": don't bother with the open "standard", just leave the connector open. Use dustcaps to protect from dust, not for calibration.I hasten to add that of course a properly designed open standard for higher frequencies should be shielded (and some care goes into doing it in a way that capacitance is reduced), because the open connector eventually becomes an antenna otherwise. But we are talking 5-6GHz+ there.Quote from: Mechatrommer on November 19, 2020, 12:21:05 pmYes, the test port is (usually) female, but then most often there is a M-M test cable to connect to the DUT. And you really should calibrate at the end of the cable, not at the VNA port. "Converting" a cal kit with a F-F adapter will degrade performance significantly.Quote from: Noy on November 19, 2020, 12:48:29 pmAs you can see from the Rosenberger kit, the individual parts are not exactly free even without the characterization (if you want reliable parts from a reputable brand). And that is re-purposing jelly-bean parts like a thru for an open. Having a purpose-built open standard made in the really low volume we are talking about would be prohibitively expensive. And then you need an expensive VNA with a reference cal kit, pay for regular calibration and maintenance and pay for the lab technician who actually does the measurements.

author: Noy
author_rank: Frequent Contributor
timestamp: November 19, 2020, 01:24:46 pm
content: As you can see from the Rosenberger kit, the individual parts are not exactly free even without the characterization (if you want reliable parts from a reputable brand). And that is re-purposing jelly-bean parts like a thru for an open. Having a purpose-built open standard made in the really low volume we are talking about would be prohibitively expensive. And then you need an expensive VNA with a reference cal kit, pay for regular calibration and maintenance and pay for the lab technician who actually does the measurements.For sure, i thought something like "calibrated" VNA with a "pogo plug SMA" and a machine putting it on the pogo plug, measure the value write it down into an excelsheet and throw away, put the next onto the pogo plugs.. something like that. "Fully automized" than calkits with SMA for <6GHz would be cheaper...

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 19, 2020, 01:35:23 pm
content: Quote from: switchabl on November 19, 2020, 01:13:48 pmimho no, except with extra effort to screw unscrew for connection and reduce usable life of the connectors. with good continuity/connectivity and good quality 50 ohm Zo thru, connecting to Open and Short will only increase its offset length, the rest of parameters are still the same. connecting to a good Load will still appear 50 ohm to the VNA. but well, this is true given the CAL set is of descent quality, if not, even a SMA cable or the sacrificial adapter connected to your VNA can look funny. this can quite visible beyond 3GHz and much lower with nonsense hunglow grade. ymmv.

author: switchabl
author_rank: Frequent Contributor
timestamp: November 19, 2020, 01:35:52 pm
content: Quote from: Noy on November 19, 2020, 01:24:46 pmHa, unfortunately, that won't work. There are some "snap-on" RF connectors, but they won't mate with SMA. Especially for calibration purposes, there is just no way around properly tightening it to a matching connector (with a torque wrench).Also, even if it were technically feasible, how many of those do you think you could sell? This is a tiny market.

author: Noy
author_rank: Frequent Contributor
timestamp: November 19, 2020, 01:49:33 pm
content: Thx for all the clarification.I think i will go with the Mouser Parts and will not get Male-Male thiny + box.I don't know for what i need this Male-Male Adaptor. Everything i use (cables are Male - Male, PCB connectors everytime female..) so i don't know for what i can use it.. So i will go for single buy (especially i have to order some parts from mouser already..).And if i need such a adapter (maybe i will calibrate without a cable at the VNA Port with the N->SMA Female Adapters (https://www.delock.de/produkt/89983/merkmale.html)) i can use a "cheap" chinese and calibrate them out or? Its the same like using a very short cable?

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 19, 2020, 02:03:58 pm
content: Quote from: Noy on November 19, 2020, 01:24:46 pmoh no, dont!..1) slight wiggling will change characteristic, and where the measurement plane will be? thats why they will ask you to buy another expensive torque wrench. if its thats easy everybody is already doing that and skip the torque wrench.2) what do you want to mass produce cal kit for? not everybody buying it. you will compete with $4 kit anyway that people buy because they think its good enough.your provided SDR links are not deep enough... i remember i saw a website at characterizing few SDR-kit, i cant find it right now... the closest thing you should read is something like this..http://hamcom.dk/VNWA/https://www.sdr-kits.net/downloads/2014-Rosenberger-Fairview-male-female-Cal-standards.zipfromhttps://www.sdr-kits.net/Female-12%20GHz-Kitsome sort of hand tuning cal kit, or to see how much batch to batch differ in characteristics. i dont read because i dont own one and afaik they dont include Ln and Cn effect into consideration. you may read yourself and decide if its good enough or what and then tell us something about it. cheers.

author: switchabl
author_rank: Frequent Contributor
timestamp: November 19, 2020, 02:25:30 pm
content: Quote from: Mechatrommer on November 19, 2020, 01:35:23 pmYes, in theory, an ideal adapter will add only delay. And to be fair a good 3.5mm air-line f-f will get reasonably close to that. Your average SMA adapter may not be that ideal. Minicircuits specifies a return loss of only >23dB @<8GHz for theirs. Now imagine connecting your nice 40-45dB calibration load on the other side and calibrating with that. Yes, that is a bit extreme, the adapter will usually be much better then the spec (especially at low frequencies), but you get the point. In particular, unless you have a cal-kit for the other side, you will not be able to check how good it actually is. Sadly so, because it would be much simpler and more economical if we could just have one cal-kit with a bunch of adapters.Now to be clear, for none-critical measurements you can get away with a lot. On a good lab-grade VNA, you can skip the cal-kit entirely, attach your cables and adapters and run the automatic port extension if you don't care about a few dB. But if you are worried about the 35dB residual mismatch you might hope for with the cheap Rosenberger kit, you should probably worry about adapters.

author: rubidium
author_rank: Regular Contributor
timestamp: May 20, 2021, 05:21:57 pm
content: Has anyone tested out the Applied EM Innovations kit?

author: 小太
author_rank: Contributor
timestamp: February 07, 2024, 08:02:28 pm
content: radar_macgyvermentionedthey bought an Applied EM kit while having access to a professional 3.5mm calibration kit... I wonder how the comparison went given that it's almost 2 years later?For reference, current prices with conversion rate £1=US$1.263ItemKirkby£GBPKirkby$USDApplied EM$USD6 GHz5997 GHz4855788 GHz513648649Torque wrench150189(included)

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: February 08, 2024, 09:14:11 pm
content: I have the 10 GHz version of the Applied EM cal kit. I made some measurements on a FieldFox 9917B that was first calibrated with a Rosenberger RPC-3.50. The Fieldfox was set to full span (30 kHz - 18 GHz) with 1601 points. I then measured the female standards from the Applied EM kit and saved the s1p files. Also grabbed an s1p from the RPC-3.50.I plotted the impedance, and it seems like the AEM kit does well up to ~10 GHz.I quit after tearing my hair out for a good 2 hours trying to figure out the METAS tools, so if someone else can use it to generate a model I'd be grateful (and maybe post a link to a tutorial?)

author: alan.bain
author_rank: Regular Contributor
timestamp: February 08, 2024, 11:26:31 pm
content: Are you trying to use VNA Tool? I had previously had issues with this and the process I got wasRight-click on the file of measurements, then select Database / Fit Calibration Standard Model (as per the screenshot)You then choose which type of standard it is and which parameters you don't want to adjust (I would suggest that initially you reduce the set size e.g. remove L2/L3 from the fit for a short) and hit "Start Optimization". If you try and fit too many it can get into "Not Responding" state which is a bit poor!

author: TheSteve
author_rank: Unknown
timestamp: February 10, 2024, 07:47:16 am
content: Quote from: radar_macgyver on February 08, 2024, 09:14:11 pmCan you give the expected/specified Z0 offset and offset delay for the Applied EM kit. As was mentioned for it to work best you should know some of the parameters, or at least enter what they should ideally be to reduce the variables.

author: 小太
author_rank: Contributor
timestamp: February 10, 2024, 09:01:30 am
content: Quote from: TheSteve on February 10, 2024, 07:47:16 amThey posted values inthis postas an attachment.TL;DR for the female load is offset Z_0=54.16Ω and delay=4.77psI'll try to derive calibration parameters myself with the data too in a few days, if nobody else has done it by then

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: February 12, 2024, 03:35:04 am
content: Per the PDF included with the kit, Z0 offset is 54.16 ohm, delay is 4.77 ps, and loss is 10 Gohm/sec for the female load.I ran the IN3OTD Octave scripts with the max frequency set to 10 GHz, and got Z0 offset = 54.5 ohm, delay 5.37 ps and loss of 20 Gohm/s. I suspect the optimization is not converging on a good solution since it hits various bounds (in the case of the run I included the results from, the upper bound for loss was 20 Gohm/s).

author: 小太
author_rank: Contributor
timestamp: February 22, 2024, 03:35:18 am
content: Here are the fitted values by METAS VNA Tools for the entire 0~18GHz range.The Applied EM kit is only specified up to 10GHz though, so this is just for educational purposes and not a commentary about the kit quality(I'll do a proper 0~10GHz version in my next post)Results have been plotted in Mathematica with equations from Keysight application note 1287-11 "Specifying Calibration Standards and Kits"."Given" values are those included with the Applied EM kit (as reportedhere), while "Fitted" are those VNA Tools generatedShort FOffset Z0(Ω)Offset delay(ps)Offset loss(GΩ⋅s-1)L0(10-12H)L1(10-24H⋅Hz-1)L2(10-33H⋅Hz-2)L3(10-42H⋅Hz-3)Given51.5683.612.57-889.079989.259983.11-1413.8Fitted51.52481.1396.2800-909.96111076-14204340.48Open FOffset Z0(Ω)Offset delay(ps)Offset loss(GΩ⋅s-1)C0(10-15F)C1(10-27F⋅Hz-1)C2(10-36F⋅Hz-2)C3(10-45F⋅Hz-3)Given5076.371.96-351.35-39471326.61-507.08Fitted53.54967.4422.787146.597-9005010138-358.16Load FOffset Z0(Ω)Offset delay(ps)Offset loss(GΩ⋅s-1)Given54.164.7710Fitted54.2538.4764-11.561P.S., Equations from Keysight application note 1287-11 converted to Mathematica formCode:Zr = Quantity[50, "Ohms"];(* Equations 1.1 and 1.4 *)\l = \l + I \l;\1 = (Zc - Zr)/(Zc + Zr);\T = (ZT - Zr)/(ZT + Zr);\i = (\1 (1 - Exp[-2 \l] - \1 \T) + Exp[-2 \l] \T)/(1 - \1 (Exp[-2 \l] \1 + \T (1 - Exp[-2 \l])));(* Equation 1.10 *)\l = (offsetLoss offsetDelay/(2 offsetZ0)) Sqrt[f/Quantity["Gigahertz"]];\l = 2 \ f offsetDelay + \l;Zc = offsetZ0 + (1 - I) (offsetLoss/(4 \ f)) Sqrt[f/Quantity["Gigahertz"]];(* Equations 1.12 and 1.13 *)ZS = I 2 \ f (L0 + L1 f + L2 f^2 + L3 f^3);ZO = 1/(I 2 \ f (C0 + C1 f + C2 f^2 + C3 f^3));(* Example usage with OPEN parameters *)\i /. ZT -> ZO /. {C0 -> Quantity[46.597 10^-15, "Farads"],C1 -> Quantity[-90050 10^-27, "Farads"/"Hertz"],C2 -> Quantity[10138 10^-36, "Farads"/"Hertz"^2],C3 -> Quantity[-358.16 10^-45, "Farads"/"Hertz"^3],offsetDelay -> Quantity[67.442, "Picoseconds"],offsetLoss -> Quantity[2.7871, "Gigaohms"/"Seconds"],offsetZ0 -> Quantity[53.549, "Ohms"],f -> Quantity[f, "Gigahertz"]};S11 = % /. Cases[Variables[%], v_ /; Head =!= Quantity -> v -> Quantity[v, "DimensionlessUnit"]] /. {Quantity[v_, "DimensionlessUnit"] :> v,Quantity[v_, 1/"DimensionlessUnit"] :> v,Quantity[v_, Sqrt["DimensionlessUnit"]] :> v};Plot[Abs, {f, 0, 18}, AxesLabel -> {"Frequency (GHz)", "|S₁₁|"}]

author: 小太
author_rank: Contributor
timestamp: February 22, 2024, 04:11:33 am
content: Same thing as above, but fitting was limited to just 0~10GHzShort FOffset Z0(Ω)Offset delay(ps)Offset loss(GΩ⋅s-1)L0(10-12H)L1(10-24H⋅Hz-1)L2(10-33H⋅Hz-2)L3(10-42H⋅Hz-3)Given51.5683.612.57-889.079989.259983.11-1413.8Fitted52.31985.3251.0887-965.37-6172329349-2997.3Open FOffset Z0(Ω)Offset delay(ps)Offset loss(GΩ⋅s-1)C0(10-15F)C1(10-27F⋅Hz-1)C2(10-36F⋅Hz-2)C3(10-45F⋅Hz-3)Given5076.371.96-351.35-39471326.61-507.08Fitted52.27777.4471.2253-309.12-12284219.52-456.68Load FOffset Z0(Ω)Offset delay(ps)Offset loss(GΩ⋅s-1)Given54.164.7710Fitted 1*77.7750.76737340.06Fitted 2*54.1426.239110.000* The "Load F" fitting decided to produce stupid values initially, so I ran it again but forced the offset loss to 10, and it gave more reasonable values. Both results are shownI'm not really qualified to make a conclusion here (I'm too inexperienced), but if I were to make one anyways:- Assuming the VNA was calibrated correctly with the Rosenberger kit (and kit was within spec)- Applied EM's short and open have calibration coefficients that seem fitted to a max of 6~8GHz rather than all the way up to 10GHz- Applied EM's load coefficients seem to be way off- Ignoring the load coefficients (I haven't worked out how to apply them to measured data yet), the load only has a return loss of ≥36dB up to 4GHz, and it progressively gets worse until 29dB at 10GHz, which doesn't sound like it's within spec

author: EE-digger
author_rank: Frequent Contributor
timestamp: February 23, 2024, 06:33:30 pm
content: You can also ask yourself how good your results have to be. I've done a lot of chip antenna layout and tuning work. After cal to the end of my VNA cable with SMA standards, I still have to extend it over an SMA to U.FL to another U.FL on the pcb.In a case like this, you're better off creating your own open, short load on the pcb itself. Then, just put an RF short on the last connector and run auto or manual compensation for the short.added - and, of course the frequencies you're working on will affect this big time

author: joeqsmith
author_rank: Super Contributor
timestamp: September 07, 2024, 05:14:32 pm
content: Quote from: radar_macgyver on February 08, 2024, 09:14:11 pmSorry for the necropost. I had watched the METAS video and they did not go into any details on how to accomplish this. Going through this thread, I too am curious how to derive the coefficients for an unknown set.The last time I did this, I used one of the local members Matlab scripts. I would like to try this with METAS. Any pointers to save my hair are appreciated.Also:https://www.eevblog.com/forum/testgear/kirkby-calibration-kit-alternatives/msg1437115/#msg1437115SUJ, nice job with the waveguides. I am on a similar path.

author: shabaz
author_rank: Frequent Contributor
timestamp: September 07, 2024, 07:09:58 pm
content: Not read the entire thread (too long!) but I was in a situation where I had an OK-ish quality, new OSL Tee, but without the coefficients. I asked Dr. Kirkby nicely, and he was kindly willing to measure it and provide the coefficients for me. The price was extremely reasonable (this was about five years ago). So, that might be an option for the cases where someone's ended up with a cal kit (say from eBay) which might accidentally be missing the data.Recently I've been using theSDR-kits cal kit(PDF doc), but have not exercised them beyond 1 GHz yet. The kit is not bad for what it is, however, the supplied 50-ohm load in my case had 48.52 ohm DC resistance. That's normally not an issue (there's another thread on the topic elsewhere) and some VNAs allow for entering that value, but if that's a concern (personally, I wanted closer to 50 ohm because I also tend to use it for various purposes at low frequencies, from DC to tens of kHz) then the very easy solution is to just replace that with your own 50-ohm load, e.g. Huber & Suhner ones are often much closer at DC.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 07, 2024, 11:32:29 pm
content: A much better thread:https://www.eevblog.com/forum/rf-microwave/calculating-correction-data-for-an-unknown-vna-calibration-kit/

author: 小太
author_rank: Contributor
timestamp: September 08, 2024, 11:10:30 am
content: Quote from: joeqsmith on September 07, 2024, 05:14:32 pmI just followed the instructions by alan.bain posted a bit further up:(You have to open a measurement file first)Quote from: alan.bain on February 08, 2024, 11:26:31 pm

author: vsilves
author_rank: Regular Contributor
timestamp: January 29, 2025, 09:51:53 pm
content: Novice here and recently found this thread and looked at Dr. Kirkby statement back in 2018 with respect to DC resistance (DCR) of 50Ω loads, which I trust to be "correct."<Dr. Kirkby QUOTE>I feel that's irrelevant, as it does not indicate the RF performance at all, because the real part of the resistance is not independent of frequency....S11 and S22 measurements can't be expected to be very accurate at low frequencies, as the return loss of the attenuator is very good. A high return loss means a high measurement uncertainty. As the frequency rises, so the return loss of the attenuator deteriorates, and the S11 and S22 measurements are more meaningful. But the S21 measurement is useful at all frequencies.</Dr. Kirkby QUOTE>I evaluated all my chinisium 50Ω loads using a converted SSA3021X+ for S11 return loss (RL) after performing an OSL calibration with the presumably better Mini-Circuits ANNE-50L+ DC-12 GHz Precision 50 SMA-M load --see attached PNG files--. Used a Fluke 289 with a female SMA connector to banana plug DIY rig to measure DC resistance (DCR) relative to one of my NanoVNA F-3 "shorts" as offset --file name includes the DCR measurement for each load--. Number 9 file is actually one of a set of 5 terminators, all with similar RL and DCR profiles (could not upload more than 10 files to this forum).After getting the Mini-Circuits load and reading the comment about RL, I consider the job of 50Ω loads to absorb energy and return as close to 0 as possible (opposite of open and close, required to return as much as possible, 1 ideally). Based on this, the ANNE-50L+ (mostly better than -40 dB RL), and my Long1 and Long2 (better than -35 dB) are the only loads I plan to use for calibration of NanoVNA and Siglent SVA. Dot1, dot2, dot3 could be used. Most of these arrived with NanoVNA F2, F3, TinySA, or Ultra, I think, but lost track of which is which.All the other 50Ω loads I have appear to be made of copper-chinisium alloy and show appalling RL, reflect significantly more energy than the 50Ω loads in the previous paragraph.These results are very surprising to me, and made me change my prior assumptions. I previously focused exclusively on DCR and considered my L1, L2, L3 the best loads for OSL calibration based on their proximity to 50.0Ω DCR. Now I consider them unusable based on their poor RL.I purchased an N Type OSL set from Amazon and it was similarly 2% off on DCR, but I may have misjudged it, and now I need to measure how it responds to RL by observing its S11 and completely disregard its DCR.Eventually, I will find time to OSL calibrate the Siglent SVA using one or more poor RL 50Ω loads and then measure all the others to see if I draw different conclusions.

author: vsilves
author_rank: Regular Contributor
timestamp: January 30, 2025, 02:47:29 am
content: Follow up post. The N-type load in the Amazon cal set turned also horrible with respect to RL (only better than -20 dB RL at low frequencies). Had to remove N male to SMA female (calibration plane) to attach the N-type load.Decided to look at all my loads in the Smith chart as well (after recalling previous calibration, re-confirming previous RL values, using same N to SMA calibration plane --no cables--, etc.). All my good loads (Mini-Circuits, Long1..2, and Dot1..3) had exceptional single dot on the center of the Smith chart all the way up to 3.2 GHz. Dot2 distinguised itself as-good as better ones. Dot1 and dot3 a bit worse but also great. All others (L1..3, Long China1..5, and N-type): oh my gosh, big arc, nothing close to constant impedance (some with inductance and some with capacitance). The Long China even got me an open from time to time (it's not a bug, it's a feature, still on return window but keeping as examples of what loads should NOT be).Attached one example each for each type of load name tested (rest on same group had similar profiles). These results sort of confirm which 50Ω loads are good and which ones are junk.

author: hendorog
author_rank: Super Contributor
timestamp: January 30, 2025, 05:53:47 am
content: Comparing loads is a bit tricky - it ultimately just a comparison against the load you calibrated with - along with added noise and drift which are introduced by the VNA you use.The first measurement, of the MC ANNE load, which is what you used for the cal, tells you something about the stability of the VNA but it tells you nothing about the load itself.Attached is a screenshot showing:ANNE-50+ load in yellowANNEF-50+ in blueThe cal was SOLR (with isolation as a test), and the cal kit was a combo:Female cal parts: 85033Male cal parts: 85052CThe second screenshot with the blue trace only shows the Female cal load re-measured after being disconnected and re-connected again.The next screenshot is from METAS, and is a NanoVNA cheapo load (measured a while ago using an adapter to protect the VNA connectors)The next screenshot is the best INMET load I have measuredThe final one is the Load from a mid priced Taobao cal kit.

author: tautech
author_rank: Super Contributor
timestamp: January 30, 2025, 06:28:19 am
content: Quote from: vsilves on January 30, 2025, 02:47:29 amChanging the Smith chart scale can reveal some surprises and make the trace large enough to place markers on.Good idea to capture at a 1U scale first then have something to compare zoomed in captures to.

author: hendorog
author_rank: Super Contributor
timestamp: January 30, 2025, 07:31:28 am
content: Here is the calibration load measured on the SSA3075XR with 100 averages.No disconnect/reconnect done.Male cal kit same as before.Without 100 averages it looks about the same as vsilvesAnd the same ANNE load *** Edited initial image was not the same load ***

author: joeqsmith
author_rank: Super Contributor
timestamp: January 30, 2025, 01:32:19 pm
content: Quote from: vsilves on January 29, 2025, 09:51:53 pm"presumably" I assume you read and understood the datasheet. So you know what they spec them to worse case.Data showing two of the best ANNE terminators compared with a few others. Reference is vintage Agilent PNA calibrated with 85033e standards. The other six ANNE loads I have were not near that good. Sorting was a cheap way to get a decent load standard.https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg3323942/#msg3323942Making various DC measurements for loads.https://www.eevblog.com/forum/testgear/nanovna-v24-sma-cal-load/Recently I attempted to tighten up my measurements with the low cost VNAs, using a couple of T-Checks to verify the quality of the calibration. This was a comparison between the low cost VNA and my PNA. Even after adding support for databased standards, characterizing my low cost standards, verifying my math against Agilents..... when it was all said and done, the VNA was the limiting factor, not the cheap standards I use with them.https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg5665155/#msg5665155More discussion on the ANNE terminators.https://www.eevblog.com/forum/projects/20db-rf-attenuator-seeking-feedback-to-improve/msg3093968/#msg3093968

author: vsilves
author_rank: Regular Contributor
timestamp: January 30, 2025, 04:15:53 pm
content: Appreciate the hints, measurements, and comparisons from more experienced folks.Thanks @tautech for hint on zooming into Smith chart (have never done it yet, but makes sense, and should be easy to figure out).@joeqsmith: Haha, I did "presume". I had seen ANNE specs, but did not take into account or recall numbers during my measurements (complete gamble and bad move on my part, so thanks for pointing it out). Looking at ANNE specs again I see min RL is only -26 dB (DC-4GHz) but that is, of course, for 4 GHz. Typical is -30.84 dB (4 GHz), and closer to my upper bound -33.81 dB (3.05 GHz). Higher use I probably have is 2.4 GHz wifi so around -35 dB typical. Your two ANNE traces and hendorog's M and F ANNE traces are roughly in line with typical specs. I see now that I got a not so bad ANNE, could be better, but could also be a lot worse. In the land of the blind (i.e., my basement), my one-eyed ANNE is king.After yesterday measurements, I had asked ChatGPT what RL to expect for a good 50Ω load 0-3.2GHz and the answer was high-quality load (metrology-grade, precision loads) better than -45 dB up to 3 GHz. Standard lab-grade (high-quality but not metrology grade) better than -35 dB to -40 dB across 3.2 GHz. General purpose 50 Ω terminations (not for precision calibration) -30 dB or worst at higher frequencies. Based on this I keep my modest aim on getting loads -35 dB or better, if I can help it.For my calibration/measurements, I had increased the trace point to 2000 for 0-3.2GHz. Surprised hendorog uses the default 201 points for 0-7.5GHz. On the other screen covering ANNE-50+ and ANNEF-50+, S11 and S22 respectively, to 8.5 GHz I cannot see the number of points. Should not make a hughe difference but couldn't that miss some peaks or valleys, if present?Hendorog's female ANNE dropping roughly from -40 dB to -75 dB after removal and reinsertion is crazy, no? When I measured the Smith charts I first looked at the RL (after power cycle, calibration recall, had even removed N-to-SMA and put back to restore same cal plane, etc) and the RL for all loads looked indistinguishable from the original uploaded measurements (to my uncalibrated eye).Hendorog's cal load on SSA3075XR with 100 averages is showing roughly below -60 dB (around -70 dB even), and without averages roughly at -40 dB (similar to my measurement). Question. Shouldn't we care about the worst case RL and engage max hold instead of any averaging? (I think I'm gong to try that, unless I hear it makes no sense).In my original measurements for RL, I had 10 averages on, but at around 1-2 sec sweep time (cannot recall) I probably did not even wait all 10 runs before taking screenshots. For Smith I do not think I turned on averaging at all. On hendorog's measurement to 7.5GHz of the calibration load I see the same (lots of) jagged edges (be it noise or uncertainty??), same as the measurement of my ANNE cal load (immediately after calibration without removing it). Curious to know why measuring whatever cal load is used results in a more jagged trace than measuring loads other than the reference cal load, independent of overall badness of RL of each load. (Will try to cal with my Long1 and then measure my ANNE, expect the jaggedness to go away, even if I don't know why).@joeqsmith I like your "the VNA was the limiting factor, not the cheap standards I use with them" comment and since I have a NanoVNA-F3 will try and experiment to see what I find now that I know a bit more about he quality of my loads (how good or bad the NanoVNA is compared with the Siglent, using same loads).Just learning all this and, overall, I am very pleased nobody mentioned DCR in their responses, a topic that was very popular on older posts in this thread ;-)

author: joeqsmith
author_rank: Super Contributor
timestamp: January 30, 2025, 04:46:53 pm
content: Quote from: vsilves on January 30, 2025, 04:15:53 pmMine were below 40dB compared with a metrology grade standard on a name brand VNA. Below 40 is pretty much in the noise floor. How do you know what yours is? You would need something as a reference to compare it with.Quote from: vsilves on January 30, 2025, 04:15:53 pmAfter upgrading the Agilent for 9GHz and running through the alignment, I borrowed a set of metrology grade standards that I transferred to my E-Cals. I maxed out the memory on them using a high sample count. IFBW was cranked way down. I also tried two different power levels to see if there were any improvements. That was what I used to then re-characterize the low cost standards.I think for the T-Check experiments, I limited the number of points to 1600. The problem isn't the T-Check stability, its the low cost VNA has a lot of noise as I get beyond 4GHz.Quote from: vsilves on January 30, 2025, 04:15:53 pmNo. See response below:Quote from: virtualparticles on December 09, 2020, 07:09:36 pmQuote from: vsilves on January 30, 2025, 04:15:53 pmI did provide a link for DCR measurements. That was the same thread where OP was talking about SWR three places beyond the decimal point. There was a recent thread running from ham trying to use some low cost terminators for a standard. You should try using the search engine. There is a lot of useful information available.

author: hendorog
author_rank: Super Contributor
timestamp: January 30, 2025, 07:00:32 pm
content: Quote from: vsilves on January 30, 2025, 04:15:53 pmAs pointed out by virtualparticles, the return loass of your calibration load is what dictates how accurately you can measure return loss in your DUT.See image attached showing the error, from this document:https://markimicrowave.com/assets/e01dd483-b079-4da5-9d03-79b6db1f5969/directivity_and_vswr_measurements.pdf(In an OSL calibration, when the Load is assumed perfect, the Directivity error is exactly the same as the true Return Loss of your calibration load)Quote from: vsilves on January 30, 2025, 04:15:53 pmPotentially, but would have made that measurement and calibration take significantly longer.In my first post, which had measurements done on a Siglent SNA, I used 500Hz IFBW, no averaging and 2001 points. Sweep time 3.5 seconds.In the second post, which had measurements done on a Siglent SSA, I used 100 averaging and 201 points. Sweep time 6.4 seconds (incl averaging). Sweep time would have been 64 seconds with 2001 points and 100 averages. Not worth it for measuring a load which was already known good.The SSA does not permit IFBW adjustment, much to my dismay.Couple of further points:Slowing down the measurements with too much averaging and/or too many points on a low end VNA can be worse because they drift more.Taking more time to measure means the instrument can drift quite far between completing the Load calibration step, and completing your measurement.The SNA is very stable in comparison to the SSA.And of course:Something which has a sharp enough notch response that you cannot see it in the GHz range with 200 points means it has about 37 MHz bandwidth. Seems a bit unlikely to happen by accident in a load.Quote from: vsilves on January 30, 2025, 04:15:53 pmSorry I was not very clear and so you missed the point I was making with that image.The -75dB images in both of my posts were of the same Agilent load which I used in the calibration. In the first post, from the SNA, I disconnected and reconnected the same load used for the calibration. In the second post it was just left on the port and measured.This will always result in an excellent return loss, as the VNA is almost always set to assume the cal load is perfect.If I had not disconnected and reconnected it, and instead made the load the last measurement in the calibration, then the return loss trace on the SNA can be below -100dBThis number tells us nothing about the calibration load itself. I could have used the ANNE load or an ultra cheap NanoVNA load for the calibration, and I would get the same result.Quote from: vsilves on January 30, 2025, 04:15:53 pmThe spikes are due to the noise of the VNA.So max hold will measure the peak of the VNA noise as well as what is measured from the DUT. It will also capture the drift of the VNA very nicely.When you are measuring the same load you used in the calibration, then by definition there is no reflection from the DUT being measured. Any reflection is calibrated out - because it is used to determine the Directivity error of the VNA.Quote from: vsilves on January 30, 2025, 04:15:53 pmTry on different VNA's:OSL calibration and then measure the same load without disconnecting it.See how low you can get the trace by messing with averaging and IFBW (if available), and how long it stays in one place. That tells you something about the quality of the VNA.Quote from: vsilves on January 30, 2025, 04:15:53 pmThis is where the Smith chart is useful. You can turn on a marker and you should see a resistance close to the DCR of the load _when the marker is close to the DC end_ of the frequency range. Then observe how it changes as you increase the frequency.

author: vsilves
author_rank: Regular Contributor
timestamp: January 30, 2025, 09:47:03 pm
content: > I did provide a link for DCR measurements.Sorry, I genuinely missed it. However, my point was that I continue to agree with Dr. Kirkby's statements and DCR should not matter so long as low frequency response is not affected, and for that you only need to look at RL, not DCR.> How do you know what yours is? You would need something as a reference to compare it with.Definitely agree that I don't know without a better reference to compare to.In fact, I calibrated SVA with (crappy) China1 load and that made (awesome) ANNE looked pretty crappy (1st pic below). Shows about -12 dB RL (at roughly 3 GHz). ANNE min specs are -26 dB (at 4 GHz, so should be way better at 3 GHz) and typical -33.81 dB (at 3 GHz). My conclusion, unless ANNE is broken, which I believe it is not, then the China1 is as crappy as I suspected. Even if China1 cal makes China1..5 RL appear decent (a bit worse than -30 dB RL --2nd pic below).I remembered I have an SMA 2W 10 dB attenuator rated to 6GHz (on label) and it may be worth measuring with different reference cals. The 3rd pic shows the attenuator's insertion loss (flat at roughly -10 dB, with a -10 dB TG input). Using normalized tracking generator function, so not dependent on any external load. Looking at S11 of the attenuator with a (presumably good similar to ANNE on previous tests) Long1 load OSL cal, I get a flat response roughly at -20 dB RL (see 4th picture). Port 2 of attenuator was open. This all makes sense in my mind: -10 + (-10) = -20. Given that the first TG measurement did not depend on the load, any load that agrees with TG must be right.Then, if I measure the same S11 of the attenuator after a China1 OSL calibration, results get clearly off from what the TG said (picture 5 below). Wildly swinging from -22 dB to -7 dB.I feel pretty good about this. Like I just proved a theorem or something. But not as good as a known good cal reference. There might be fallacies in my logic, and, as I hobby-study more, I hope to find out one way or the other. I will probably not find any better cal kit, and not worth the $$$ for my hobby purposes.Just saw hendorog posted replies (still have to read and study to see if I can comprehend). Again, thanks for all the hints. I learned a lot reading this blog, and Google, over the years. Finally posting some. Honored to get dialog with the big guns, haha.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 30, 2025, 10:28:50 pm
content: Quote from: vsilves on January 30, 2025, 09:47:03 pmConsider that when I received that first NanoVNA in 2019, I used the supplied standards to create a demonstration video of it. I also used the ideal model (told the VNA the standards were perfect). I made several measurements of various passive networks and everything measured as it should. Often I won't calibrate the VNA, or it is the last step. Over the last four years, I've ran a lot of tests and shown a lot of data using these cheap VNAs and poor quality standards. I'm the last person that would suggest you need to spend a lot of $$$ for a hobby and learning how to use a VNA. That's the whole point of these cheap VNAs.As long as you understand the limitations of your particular VNA (for example not being able to make narrow band measurements with the V2Plus/LiteVNA, drift, effects of the squarewave drive on your circuit) you shouldn't have any problem. The most common problem I see in the forums is the hams connecting them to their antennas and taking them out with ESD. Even then, they damage a $200 at most. Good learning experience and may save a costly repair bill in the future.

author: vsilves
author_rank: Regular Contributor
timestamp: January 31, 2025, 02:57:07 am
content: When I said this in my previous post, -20 made sense for TG insertion loss test only (shown as -10, instead of -20, since it was normalized with -10 dBm TG output). For the SVA S11 measurement I had no idea why it should, or should not, be -20, but it looked like a very round number (coming out of my fourth point of contact).> This all makes sense in my mind: -10 + (-10) = -20.Chit chatting with ChatGPT afterwards about what to expect for the S11 on an ideal terminator of known value with no parasitics and open port 2, it spit out some formulas to calculate the reflection coefficient as Γeff = Γopen x 10 ^ (-2 A ÷ 20), where Γopen = 1 (full reflection since port 2 is open), factor A is the attenuation, and factor 2 accounts for the attenuation happening twice on the way to port 2 and on the way back from port 2, which for a 10 dB attenuator would be Γeff = 1 x 10 ^ (-2 x 10 ÷ 20) = 10^-1. Then from that it calculated the S11 as S11 ‎ = 20 log10 |Γeff| or S11 ‎ = 20 log10 (10^-1) = 20 x (-1) = -20 dB. Basically, this calculation will always be twice whatever the value of the attenuator used.Looking at the SVA1032X Tech Sheet specifications, I see the dynamic range for the directivity of the calibration S11, Log mag, Average=50, >50MHz, > 40 dB. Which I think I should interpret as: there is a -40 dB floor of how low I can see S11 reflections, (I assume) relative to the output power of the TG (port 1 of SVA). Not sure (until I look) if the amplitude button/menu shows or controls output power during S11 measurements.Earlier, I had measured the S11 (pic 1) and S22 (pic2) of a cheap SMA 10W 40dB attenuator (rated to 3 GHz by vendor). Based on the dynamic range limitations of the SVA, I think I cannot see or do anything with respect to the S11 of this 40 dB attenuator (i.e., cannot expect to see -80 dB).My arsenal only has two 3 dB attenuators, and two 30 dB attenuators left. A single 30 dB may also lay beyond the S11 dynamic range. My plan for tomorrow is to measure the S11 of one 3 dB attenuator alone (should read -6 dB), two 3 dB attenuators in series (should read -12 dB), and the 10 dB attenuator in series with a single 3 dB attenuator (should read -26 db). I think it will be interesting to see how the S11 RL trace correlates with the S22 insertion loss of the attenuators.

author: vsilves
author_rank: Regular Contributor
timestamp: January 31, 2025, 04:07:28 am
content: Specs in Sysjoint NanoVNA-F V3 manual show better S11 dynamic range (50 dB) than Siglent SVA1032X (40 dB), if true.> NanoVNA-F V3 is a Portable Vector Network Analyzer (VNA) with frequency range of 1MHz ~ 6GHz. It can be used for S11 and S21 measurements. The S21 dynamic range of NanoVNA-F V3 is 65 dB, while the S11 dynamic range is 50 dB.Further down a table in the manual states:> S11 dynamic range:> 50dB for < 3GHz> 40dB for > 3GHzWill try and repeat whatever I get with SVA1032X later with the NanoVNA-F V3. My goal is to see how the load in the OSL calibration affects results for S11 measurements of port 2 open attenuators, in order to judge the quality of the 50Ω loads themselves.

author: hendorog
author_rank: Super Contributor
timestamp: January 31, 2025, 06:22:31 am
content: Quote from: vsilves on January 30, 2025, 09:47:03 pmSomething that I discovered a while ago.If you have two loads and you:Preset the VNACalibrate with Load A and then measure Load B and record the trace.Preset the VNACalibrate with Load B and then measure Load A and record the trace.Both traces are the same.If I understand correctly, then you did this. But the traces are not the same.As another sanity check, even the cheap loads generally have decent Return Loss at very low frequencies (your sweep starts at 100kHz)Your cheap load was around 50.9 ohm - say 51 ohms. That should get you -40dB return loss.The ANNE load should be below -40dB return loss there.So the sanity check suggests your recent screenshot should be better than what it is. (The first screenshot in post 226)

author: vsilves
author_rank: Regular Contributor
timestamp: January 31, 2025, 07:05:07 am
content: Rechecked screenshots and yes RL traces were different. Will repeat with SVA1032X and also NanoVNA F V3 and post results in a couple of days.> Preset the VNA> Calibrate with Load A and then measure Load B and record the trace.> Preset the VNA> Calibrate with Load B and then measure Load A and record the trace.Looking at RL trace of cheap load (China1) after calibration with ANNE, I see -40 dB only to less than half a division (10 divisions for 3.2 GHz) so less than 160 MHz. Then ramps up roughly -15 dB around mid span, and maybe -8 dB at 3.2 GHz. First picture below.Conversely, looking at trace of ANNE load after calibration with China1, S11 starts at slightly better than -30 dB at near DC, ramps up to maybe -18 dB at mid-span, and ends at around -9 dB at 3.2 GHz. Second picture below.Picture 3 shows the specs for SVA1032X. Could you comment how you interpret the limitations for the dynamic range of S11 measurements on SVA mode and what S11 RL levels the SVA1032X should be able to measure?Picture 4 is the ANNE S11 RL after calibration with a presumable decent/regular load (other than ANNE itself). Shows that it stays below -40 dB across entire span.Picture 5 is the cheap (China1) S11 RL after calibration with same decent/regular load (Long1). I don't have a China1 RL after Long1 cal, but picture below shows China2 (very similar set of 5 China bad loads).Again thanks for kind and helpful comments!

author: hendorog
author_rank: Super Contributor
timestamp: January 31, 2025, 07:37:20 am
content: Something is off with the measurement in your second picture.Can you try the process again:Preset then calibration with China1 and then measure ANNE and take a screenshotPreset then calibration with ANNE and then measure China1 and take a screenshotMake sure you don't change anything - use the same open and short and choose the same cal kit in the SVA for both.

author: hendorog
author_rank: Super Contributor
timestamp: January 31, 2025, 08:16:36 am
content: Quote from: vsilves on January 31, 2025, 07:05:07 amThe S11 'dynamic range' is called Effective Directivity.That is the directivity that the VNA is capable of measuring after calibration.VNA Calibration corrects the directivity error in the hardware, which is why the VNA can more accurately measure RL than you can using the SVA tracking generator and SA mode.However the error correction of directivity is _directly_ dependent on the return loss of the calibration load.Aside: You can cheat that rule on an SVA, if you have someone with a real cal kit measure your OSL standards and give you s1p files. Then you can take your own measurements on your SVA, save them as s1p files, and then do the calibration offline on a PC.Effective directivity can be measured, but requires an airline.The better the effective directivity, the more accurately you can measure return loss.The Effective Directivity spec is 40dB. If your ANNE load is better than that and you turn on averaging at least as much as the spec says you should achieve that.Attached is an image from the pdf I pointed to earlier. It shows the measurement error for a given Directivity value.See the 40dB directivity trace on the chart.

author: vsilves
author_rank: Regular Contributor
timestamp: January 31, 2025, 10:07:53 pm
content: @hendorog, I did the cal A measure B, then cal B measure A, in order to compare the reciprocal return loses. See PDFs. The RL of the opposite load is shown in step 5.First PDF is ANNE vs China1 (bad bad load in my perception) and the RL of each other does not look identical.Second PDF is ANNE vs Long1 (decent load in my perception, from NanoVNA most likely). The RL of each other DOES look identical!Thanks for your analysis and comments. I hope this means China1 is messed up and my SSA/VNA is not.

author: vsilves
author_rank: Regular Contributor
timestamp: January 31, 2025, 10:17:31 pm
content: This is the other experiment I wanted to do. OSL cal with ANNE then measure some attenuators to observe expected vs actual RL obtained.I think the observed RL meets roughly the expected RL for 3, 6, 10, and 13 dB attenuators (got roughly 6, 12, 20, and 26 db RL). Maybe no enough dynamic range for 30 dB attenuator.The idea would be to repeat this after first OSL cal with China1 to see how the expected RL is "not" obtained.

author: hendorog
author_rank: Super Contributor
timestamp: February 03, 2025, 02:57:06 am
content: Quote from: vsilves on January 31, 2025, 10:07:53 pmOk thanks for all of that effort. It that looks more sensible - not identical but the return loss charts are now fairly similar.Because there is still a difference, some inconsistency must be causing that.The Long1 pdf looks much better than the China1 pdf, both in terms of RL and the symmetry.Likely there is some sort of mechanical issue with the China1 load, the trace you get when you put it back on and measure it is quite different to the others.Other things to check, the N-SMA adapter, the connections are not clean, something is not tight, have you left to warm up for an hour or so?Check that nothing changes when you tap/wiggle the load (you will need to turn off averaging and have a low number of points to see anything)The 180 degree phase rotation which is visible on your Smith chart images is correct I believe.You can do the same test with the attenuator instead of the China1 load.It does not matter if you Cal with the ANNE load and measure the attenuator, or Cal with the attenuator and measure the ANNE load. You should get the same trace in both cases.If you don't get the same trace, then I think something must be wrong.If you have time/can be bothered to take measurements of all of your SMA devices (incl OPEN and SHORT), and save them as s1p files with appropriate filenames, we can run the calibration offline on a PC.Please ensure the SVA has been turned on for an hour or two first and is in a place with no draughts or direct sunlight and a stable temperature.No calibration is required.50 averages and 1000 points (adjust points if you need to keep the measurement time under 10 seconds)

author: vsilves
author_rank: Regular Contributor
timestamp: February 03, 2025, 06:45:37 am
content: Quote from: hendorog on February 03, 2025, 02:57:06 amThis is a great tip, along with original tip to measure A->B and then B->A. May try with attenuator vs ANNE, but also have second (similarly good) Long2 50Ω load to try. I have a LPF, Combiner/Splitter, and a Directional Coupler from Mini-Circuits to about 2GHz and may try to match spec sheet graphs (to prove cal load is ok if specs are matched), if I can figure out how to measure. Also have a mixer but a bit harder to figure how to measure for now.Of all the possible pitfalls you mentioned, I think everything is steady and clean, except yes I may have violated not enough warm up time of instrument (for China1). May repeat, but I have observed similar behavior after 1+ hour warm up (in stable basement temp, no drafts). Two of my 5 China 50Ω loads (not this China1) intermittently show as "open" if I wiggle the core while holding the nut. This does not happen with any of my other loads. So a mechanical problem is very likely for all China# loads.Quote from: hendorog on February 03, 2025, 02:57:06 amVery interested if you could analyze any .s1p files I may generate for OSLs. It appears SVA1032X can NOT save .s1p files, only .csv files. I will figure out how to pull S11 traces using python, and generate .s1p files (which may be faster than saving .csv and processing). With that end, what would be more convenient to process for offline calibration on a PC?:1. # MHz S DB R 50frequency logmag phaseor2. # MHz S RI R 50frequency real imagOnce more, thanks for your time and comments, which help immensely a hobbyist like me.

author: hendorog
author_rank: Super Contributor
timestamp: February 03, 2025, 07:04:17 am
content: Quote from: vsilves on February 03, 2025, 06:45:37 amCopy, that makes sense with the mechanical load issue.On the SSA if I hit the File button then Save Type there is an option called SNP. If that is available in the SVA then that will save an S1P file.Otherwise yep the CSV method works and either of the two formats is fine.I think from memory you need to be in Smith Chart mode to get it to export both R + I or gain + phase in a single csv.I will use scikit-rf to do the cal, and I use it in a Jupyter notebook.The cal and then measurement can be done the two different ways on just the one set of files. That means you don't get the connection/reconnection error and so the two different cals will result in perfect overlaps.If you end up coding the extract s1p then maybe do several disconnect/reconnects of the loads and extract multiple files so that error can be viewed.

author: vsilves
author_rank: Regular Contributor
timestamp: February 03, 2025, 10:21:00 pm
content: Here are the .s1p files for a few of my 50Ω loads and my open and short SMA connectors, all in .s1p format and descriptive file names. Some with repeated removal and reinsertion (test 1, test 2, etc). Uncalibrated instrument. I had never opened any .s1p file before, but I installed a free Mac app named splotRF, and was able to open the .s1p files and verify that the Smith chart trace shown in the app looks identical to the instrument's Smith chart. Hoping I did not code anything wrong on the output files.Need to improve code. Currently pulls FREQ, LOGMAG and then PHASE, PHASE, in two goes, so it messes with any AVG when changing mode from LOGMAG to PHASE, but only takes like a second to pull the 1000 points. Need to figure out an SCPI command that will return FREQ, LOGMAG, PHASE (or FREQ, REAL, IMAG) all in one go to keep existing AVG.

author: vsilves
author_rank: Regular Contributor
timestamp: February 04, 2025, 06:17:05 am
content: The hint of using scikit-rf was both surprising and great. Scikit-rf looks very intimidating and I know nothing about it (probably need to study more theory before I can use it). However, plotting multiple .s1p files side by side as Smith, LogMag, or Phase charts using scikit-rt was so easy! I prefer this kind of rudimentary interface to fancy programs.In any case, trying not to bombard the forum with files, but I fixed my SCPI script and now I can pull RE, IMG data at once from Smith Chart view (like you said) and that pulls the 50 AVG trace or whatever trace 1 has to the .s1p file. Quick to pull (under 1 sec?), but based on your drift comment I should not let the averaging itself take too long either before I pull a trace (so reduce number of points). With some practice I should be able to pull more robust .s1p traces under various conditions.

author: vsilves
author_rank: Regular Contributor
timestamp: February 04, 2025, 09:15:09 pm
content: Just playing with scikit-rf a bit more and I think I figured out how to do offline calibrations using .s1p files. Results in attached PDF for ANNE, long1, and china1 seem to meet expected traces (identical logmag and 180º shifted phase for A <--> B). Generated traces look a lot like the actual measurements I remember. Pretty amazing that you can generate all that from only the uncalibrated .s1p files for the OSL. I had no idea this was possible until hendorog mentioned it.Unfortunately, this says nothing about the quality of the loads (without a known good reference). But I think loads of similar response are, duh, similar. Just don't know (for sure) which ones are the good and which ones are the bad.Would like to get example OSL .s1p files with good descriptions to play with. Not sure if manufacturers or users post this somewhere. I will be searching eevblog ;-)

author: hendorog
author_rank: Super Contributor
timestamp: February 04, 2025, 11:18:45 pm
content: Nicely done!Sorry I have been a bit too busy to get into this, but you have done exactly what I would have done.It was messing around with scikit-rf that lead to discovering the reciprocal relationship and the 180 degree phase change. I think it provides a nice sanity check I think.I have not seen that mentioned anywhere before, this is the first time I have posted it and thank you for verifying it.That probably means it is so obvious that everyone except me knew about it alreadyThe maths side seems to work out too.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 05, 2025, 05:11:36 am
content: Quote from: vsilves on February 04, 2025, 09:15:09 pmI'm not following but it would be easy enough to synthesize data for a set of standards. You could make them anything you like. You could then use those to calibrate your virtual VNA and then measure some virtual parts. When playing with METAS, that is basically what I was doing.I doubt this will help but when I attempting to tighten my measurements with the LiteVNA, I characterized the standards I use with it. This was done using my Agilent PNA which was calibrated using an ECAL that was characterized to some standards I loaned. The short and open standards are basically what was supplied with the LiteVNA64. The load is a mini-circuits ANNE I hand selected using the PNA and metrology grade kit. You can find the touchstone files using the dropbox link in my signature. Goto VNA_Support/Solver64/Calibration/LiteVNA64. That directory contains the data for the SOLT. These were swept from 300k to 9G. 1601 data points. 500Hz IFBW. 0dB. Format is Freq S11 dB/Ang.I used METAS to derive the coefficients for these standards. That data is hardcoded into Solver as a default. You can view it with that tool, or just recreated it with METAS.Again, I noted little difference between using the raw Touchstone files and the coefficients METAS selected. Measuring a T-Check that performed well on the PNA to 9GHz, using the same coefficients and calibrated with the same cheap standards, falls apart with the LiteVNA around 4GHz. I used the same software when running both VNAs, same math. That was also checked against Agilents built-in firmware.

author: vsilves
author_rank: Regular Contributor
timestamp: February 10, 2025, 05:29:45 am
content: Still loving skrf and got many nice plots, but looking at Mini-Circuits ZFDC-10-5-S+ (directional coupler) I'm struggling to plot "directivity" correctly using their posted .s3p file. The first picture is my logmag plot of their .s3p file. The second picture is their posted graph for directivity (a bit more detailed than the small graph in the main spec sheet). The third picture is me trying to plot directivity from the .s3p file (all in dB, plotted with a minus sign in order invert the traces and directly compare with picture 2):- First trace in red is S31-S32 (simple definition).- Second trace in blue is S31-(S32+S21), which I figured from the handbook of microwave component measurements, where it is defined as = isolation / (coupling * loss).- Third trace in green is S31+S21-S32 (exactly as stated in the Marki document that hendorog pointed at earlier).Comparing visually pictures 2 and 3 I'm disappointed as they do not seem to match very well, only very generally. Are the calculations wrong or is there no way to calculate directivity directly from S parameters and the only way is to measure S21 (logmag at CPL port) with out port open/short and then out port terminated, and then subtract?

author: hendorog
author_rank: Super Contributor
timestamp: February 10, 2025, 06:08:27 pm
content: Did you use the ANNE load to terminate the unused port?

author: vsilves
author_rank: Regular Contributor
timestamp: February 10, 2025, 06:12:55 pm
content: To highlight something that does work here is a simple DTF graph. Even though skrf does not have TDR/DTF that I know of, using a simple numpy IFFT or CZT on the Siglent VNA .s1p file (about 8.5 cable here) yields results similar to Siglent's internal DTF tool.On another note, if anybody has both (1) a known good SMA 50Ω calibration load and (2) a Siglent SVA1032X (or better yet a converted Siglent SSA3021X Plus like mine), it would be great to get two .s1p files (one with uncalibrated SVA and one with OSL calibrated SVA using same load for calibration).I found lots of .snp files in this forum and around from helpful members but have not identified any .s1p files that cover a load measured both with and without first calibration of the SVA, let alone the SVA being an SVA1032X.

author: vsilves
author_rank: Regular Contributor
timestamp: February 10, 2025, 06:16:40 pm
content: Quote from: hendorog on February 10, 2025, 06:08:27 pmThe .s3p file is the one posted by Mini-Circuits here, so I did not perform any measurements. Just trying to reproduce their results. I see other offsets between their own tech spec sheet graphs and their actual posted .s3p file data. If I try to measure with only the 2 port Siglent SVA I will try and thing what I terminate and what I do not terminate :-)https://www.minicircuits.com/WebStore/dashboard.html?model=ZFDC-10-5-S%2B&srsltid=AfmBOoo9m8hNMxr51KLYybor5wlXTa6vgoVi1vr7YaLZAOkPx3aapP_V

author: hendorog
author_rank: Super Contributor
timestamp: February 10, 2025, 07:00:44 pm
content: Oh sorry now I understand.Hmm, that is interesting.

author: Miek
author_rank: Regular Contributor
timestamp: February 10, 2025, 09:11:16 pm
content: Quote from: vsilves on February 10, 2025, 06:12:55 pmIt does by the way, here are a couple of examples:https://scikit-rf.readthedocs.io/en/latest/examples/networktheory/Time%20domain%20reflectometry%2C%20measurement%20vs%20simulation.htmlhttps://scikit-rf.readthedocs.io/en/latest/examples/networktheory/Time%20Domain.html

author: hendorog
author_rank: Super Contributor
timestamp: February 10, 2025, 09:36:53 pm
content: Quote from: Miek on February 10, 2025, 09:11:16 pmSomething to be aware of when comparing VNA TDR with scikit-rf is that scikit-rf does not use the Chirp-Z algorithm.Some more info here:https://github.com/scikit-rf/scikit-rf/issues/1093

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: February 11, 2025, 01:59:13 am
content: Keep in mind the cheap Chinese loads look like this

author: vsilves
author_rank: Regular Contributor
timestamp: February 11, 2025, 03:00:08 am
content: Quote from: Miek on February 10, 2025, 09:11:16 pmSorry, yes, I actually mean to say DTF, not TDR. I used the extrapolate_to_dc() call as the only way to add points to pre-recorded S11 data which allows to extend the time/space range. Tried many things that failed before that.Also used network.plot_s_db_time() very rudimentary to plot amplitude vs time.skrf is great, specially to ingest .s1p, .s2p, .s3p files robustly.

author: vsilves
author_rank: Regular Contributor
timestamp: February 11, 2025, 03:19:23 am
content: Quote from: hendorog on February 10, 2025, 09:36:53 pmFor my DTF script I used np.fft.ifft() for the IFFT transform and scipy.signal.czt for the Chirp-Z. Something wrong in my use of CZT, all the trace is consistently off by one frequency bin from the IFFT, and I cannot figure out how to fix it so far. Just experimenting to see if results look good.

author: vsilves
author_rank: Regular Contributor
timestamp: February 13, 2025, 06:58:09 pm
content: Quote from: Miek on February 10, 2025, 09:11:16 pmNo matter how many times I read the examples, which I had already seen before this post, I was only registering the plot_s_db() calls and thinking that skrf could only plot values vs time, but not return values over time for custom processing and plotting. Of course, I was wrong, and totally missed the skrf.network.Network.step_response() calls. Indeed, I ended up reinventing the wheel instead of relying on existing skrf functionality. I will investigate and use step_response().

author: vsilves
author_rank: Regular Contributor
timestamp: February 13, 2025, 07:55:16 pm
content: I wanted a way to tell if a coax was 50Ω or 75Ω from S11 or S22 alone. Did not find any info on how to do this online. Decided to measured the cables I had laying around on my Siglent SVA1032X, combine .s1p measurements to a single .s2p file, and study the different reflection coefficients. Eventually got a rudimentary algorithm that more or less works. I detail the steps graphically with some examples in the attached PDF. Importantly (for me), the algorithm works without letting the script know what the expected impedance is "a priori."

author: hendorog
author_rank: Super Contributor
timestamp: February 13, 2025, 09:28:14 pm
content: Here is a method which at first glance looks like what I have used before for PCB stripline.It should work with any transmission line like coax.https://chemandy.com/technical-articles/measuring-track-characteristic-impedance/measuring-track-characteristic-impedance-article1.htmAnd a manual calculator for one point:https://chemandy.com/calculators/characteristic-impedance-measurement-calculator.htmCould be worth a try to validate your algorithmEdit: Of course you can use TDR to determine impedance too.https://scikit-rf.readthedocs.io/en/latest/examples/networktheory/Time%20domain%20reflectometry%2C%20measurement%20vs%20simulation.html

author: vsilves
author_rank: Regular Contributor
timestamp: February 19, 2025, 10:36:48 pm
content: As a complete RF noob I cannot cease to be amazed at what skrf can do. Made a short list of things to try related to coax impedance measurements, based on hendorog pointers (thanks again), but got distracted with other measurements.I think I figured out how to use impulse and step time-domain responses as well as time gating. Got super distracted (obsessed?) with simulated networks. Pic1 shows a real RG58 coax measurement (.s2p) vs a simulated RG58 coax (using skrf's distributed circuit). Pic2 shows more charts of real vs sim RG58. Pic3 shows some time gating on the real RG58 only. I had no idea you could do all this!Would be nice if I could simulate a 50Ω load and use that for a simulated calibration (I have no idea this is possible or even makes sense) and measure my assumed good calibration loads.

author: vsilves
author_rank: Regular Contributor
timestamp: July 13, 2025, 03:42:44 pm
content: Recently got a LibreCal for my SVA1030X and, even though the loads in the LibreCal are nothing remarkable (first picture), the fact they are characterized with .s1p files using "Agilent Technologies,E5071C,MY46524282,B.12.04" up to 8.5GHz and the LibreCal's python script generated Siglent e-cal packet is quite large (I think uses all the .s1p and .s2p files) allows the SVA to see all my mystery loads for what they are (second picture).In the second picture, ANNE1 is the original ANNE I had (quite good). ANNE2 is a second ANNE I acquired since, and looks not quite as good but still very decent. Long1 and 2 are the loads from NanoVNA-F v2 (RIP) and v3 (still strong) that I had been using as my uncharacterized OSL kits (not bad!). BNCload is a Mini-Circuits load which is not horrible taking into account it is BNC. L1 represents a set of 3 similar loads that I had thought were better than that (previously). China1 represents a set of 5 similar loads that are as remarkable bad as I had guessed.This sort of closes the loop on my unknown loads and opens the door (for me) to characterize loads and use them with off-line calibrations and skrf.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 13, 2025, 08:00:46 pm
content: Looks like an easy way to calibrate. Appears seem less. Are the S-parameters stored on the ecal, or do you need to load them into the VNA manually? Does the manufacture provide data for each unique serial number?I found this video but there are no details.

author: tautech
author_rank: Super Contributor
timestamp: July 13, 2025, 09:06:38 pm
content: Quote from: joeqsmith on July 13, 2025, 08:00:46 pmThe Touchstone files of each Ecal are stored on the device and loaded when an Ecal calibration is performed.It is very quick and offers the advantage of much less connector wear by only needing 1 connection cycle.Using the LibreCal is a new hack of SVA/X-R analyzers in order to use a more cost efficient Ecal from other suppliers.A little more info here:https://www.eevblog.com/forum/testgear/siglent-sva1015x-1-5ghz-spectrum-vector-network-analyzer-(coming)/msg5976343/#msg5976343

author: vsilves
author_rank: Regular Contributor
timestamp: July 13, 2025, 09:27:11 pm
content: Quote from: joeqsmith on July 13, 2025, 08:00:46 pmIt does. The .s1p and .s2p files are exposed in a read-only volume (that Siglent SVAs do not look for or recognize) but if somehow you lose them, they are available online, based on serial number of device, for download (link in LibreCal GitHub).Siglent SVAs cannot read the .s1p/.s2p files as presented so a script available in LibreCal GitHub needs to be run. The script processes all the .s1p/.s2p files and creates a siglent folder in the read-write volume of the LibreCal that Siglent SVAs recognize and load during e-cal. Other e-cals can be added, for example, after characterizing any connectors or protectors added to the LibreCal SMAf ports. I think for Siglent SVAs one would need to regenerate the compressed Siglent e-cal packet in the read-write volume of the LibreCal using the new .s1p/.s2p files, instead of the original files for the bare SMAf ports on the LibreVNA.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 13, 2025, 09:36:39 pm
content: Thanks. I wonder why in 2025, why it was limited to 1202 points and even multiple data sets. Do they have software tools that allow you to re-characterize it?

author: vsilves
author_rank: Regular Contributor
timestamp: July 13, 2025, 10:37:02 pm
content: Experienced folks seem to favor as few points as possible (to reduce measurement time and increase stability) so I was glad we did not get 201 points :-). The 1202 points cover all the way up to 8.5 GHz, so, yes, I would prefer more points to 3.2 GHz (Siglent) or NanoVNA (mine is 6 GHz). But folks with higher end Siglent SVAs should be happy with coverage. Works very well, so cannot complain.Any higher end equipment can be used to re-characterize the standards on each port as they can be manually selected clicking hardware buttons. Including the Siglent SVA after e-cal. The new .s1p/.s2p would be the new characterization, which can be saved (for LibreVNA use only) and compiled into a Siglent e-cal packet on the read-write volume. Just need to follow the structure of the existing files and instructions on GitHub.GitHub has a LibreCal-GUI app. I had to use the Windows version on a virtual machine, and realized I did not need it. Mac version crashes and cannot be digitally signed for some reason. Did not try Linux version. App only allows selecting standards manually for each port, and shows a temperature graph to know when device meets limits (this can also be observed on biking LEDs).Would be neat if the NanoVNA had enough resources for a brave soul to implement e-cal magic!!! However, I think measuring the LibreVNA standards with NanoVNA and then doing uncalibrated NanoVNA DUT measurements for off-line calibrations will be easy enough (and no need for e-cal).This goes to show what @hendorog has pointed out several times in these forums. You only need a proper traceable calibration measurement of your standards for proper calibrated measurements on your VNA (off-line if VNA cannot take .s1p/.s2p files). The standards themselves can be crappy or not, and either way, that will NOT affect the resulting calibration/measurements (within reason).

author: tautech
author_rank: Super Contributor
timestamp: July 13, 2025, 10:54:06 pm
content: Quote from: vsilves on July 13, 2025, 10:37:02 pmFYI my SEM5032A 26 GHz Ecal provides 6114 points.....not specified in the datasheet.https://siglentna.com/wp-content/uploads/dlm_uploads/2023/10/SEM5000A_datasheet_DS60050_E_01A.pdfSweep in attached screenshot not associated with any Ecal info.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 14, 2025, 12:31:08 am
content: Quote from: vsilves on July 13, 2025, 10:37:02 pmI thought the support for the LibreCal was added to the Siglent firmware. Sound like they have a separate application that you run manually to select the standards. Please clarify.Quote from: vsilves on July 13, 2025, 10:37:02 pmSorry but you completely lost me with that second statement.Quote from: vsilves on July 13, 2025, 10:37:02 pmThat's correct. You can read the patents for the HP ecal or other documents on databased standards which basically describes this. It makes them cheaper to manufacture. In the case of LiteVNA, the limiting factor wasn't the standards but the VNA's hardware. As long as they documented the interface, I don't think it would take much to support it.***Of course, if you have a program today that will manually select the standards you may be all set. At least Solver supports S-parameters as well as the standard HP polynomial fit.https://coppermountaintech.com/using-a-databased-solt-calibration-kit/***

author: vsilves
author_rank: Regular Contributor
timestamp: July 14, 2025, 01:25:25 am
content: Quote from: joeqsmith on July 14, 2025, 12:31:08 amThe opposite. Somebody (guy in the video I think) reverse engineered Siglent e-cal SCPI commands and added that to the LibreCal's firmware. With the latest LibreCal firmware (and an easy to generate Siglent package in LibreCal storage), plugging the LibreCal into a Siglent SVA works seamlessly with unmodified/original Siglent firmware.LibreCal has a separate standalone app to control certain aspects of the LibreCal, but it is absolutely not necessary to update its firmware, or operate the LibreCal in any way. All LibreCal operations can be controlled with the two hardware buttons, and reading the manual to place the LibreCal in various states. The physical buttons in the LibreCal also allow selecting a port, and then selecting which standard is presented on that port, or none. LibreCal has 4 ports, each with their own OSLT available. Once LibreCal is configured with latest firmware and the necessary Siglent folder is created (by you running a python script), it is seamless. Meaning, you just turn LibreCal on, wait until it warms up (LED stops blinking), plug to Siglent USB port (to read e-cal data), connect ports 1 and 2 to Siglent VNA, load e-cal in Siglent VNA, perform S11 calibration on Siglent VNA, perform S21 calibration on Siglent VNA, done in under 10 seconds, as shown in the video. No need to press any buttons on LibreCal. In the video, a button is held, but that was for older firmware. New LibreCal firmware detects the Siglent folder and defaults to Siglent mode; you actually have to hold a button to enter LibreVNA mode instead of Siglent mode when this Siglent folder exists. All explained in its GitHub.To be clear, there is no support from Siglent or apps from Siglent to select anything. The Siglent VNA will just see and load the LibreCal e-cal (conveniently named Siglent) when a properly configured LibreCal device is plugged to USB and port 1 and 2.Quote from: joeqsmith on July 14, 2025, 12:31:08 amSorry, this is convoluted, and tedious, if not scripted. You may find some discussion about this in the forum. Basically, using the characterization .s1p files in the LibreCal as "ideal OSL." Then measuring the OSL in the LibreCal with an uncalibrated NanoVNA (or any other VNA) and calling those .s1p files "custom OSL". Allows, using some scikit-rf python magic to, measure a DUT using an uncalibrated NanoVNA, and then use the ideal OSL, custom OSL, and raw DUT measurements, to output a calibrated and traceable .s1p measurement of the DUT, as if the NanoVNA had been in fact physically calibrated with the e-Cal. So this is an off-line calibration and you may have done that with other software that I am unfamiliar with. I only know how to do this with scikit-rf and python.---Still playing with a python script I made to generate User Cal-Kit coefficient to see if it works but that is imperfect by design, when compared with using full .s1p files for the OSL standards. Still, handy if it is close enough, since it works on device (Siglent) vs off-line (scikit-rf). However, my NanoVAN has no way to enter cal-kit definitions, so using the NanoVNA in raw mode and scripting calibrations offline is very handy. I simply pull the S11 and S21 traces via USB with python as .s1p or .s2p files, and apply the calibrations to them.I refuse to use Windows (or repeatedly click UIs like a drunken monkey), so had to re-invent some wheels in MacOS via python, scikit-rf, and numpy.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 14, 2025, 11:33:41 am
content: What you described is how I calibrate the VNA's when using Solver and databased calibration. Of course it is all done live rather than post processed (off-line as you seem to describe).Quote from: vsilves on July 14, 2025, 01:25:25 amI had used METAS to create the polynomial coefficients for the cheap standards after measuring them on my old Agilent. In the end, using the S-parameters compared with the Agilent polynomial fit made no significant difference with the LiteVNA. The real limitation was the LiteVNA's hardware.https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg5656063/#msg5656063Quote from: vsilves on July 14, 2025, 01:25:25 amBasically that's all I am doing. At least with the LiteVNA, once you connect and start reading the data, you are getting the uncalibrated data.Quote from: vsilves on July 14, 2025, 01:25:25 amI've never seen a Mac used at any of the companies I have worked for and we pretty much were locked into Windows once NT was released. I've never seen a drunken monkey, but will assume there are a lot of us.

author: vsilves
author_rank: Regular Contributor
timestamp: September 03, 2025, 09:49:27 pm
content: Speaking of calibrations, I read that some vendors recommend full 90-minute warm-up time for accurate measurements (Keysight/Agilent), others 30-60 minutes (Rohde & Schwarz, Anritsu, Siglent, Copper Mountain), even others 30 minutes (Rigol, Siglent).Did some measurements on my fake SVA1032X after Librecal recall and small SMAff THRU response cal, leaving the THRU on, and pulling all data remotely to avoid disturbing instrument, cables, or DUT. Pulled S21 every 5 minutes, but only showing 10 min intervals in attached pictures. Hard to see anything at all on the first picture, traces have ripple and are too close to each other to appreciate what is going on. However, using skrf to do time domain gating around the DUT shows very nicely the S21 insertion loss and phase response slow progression and settling over time (see second picture). I interpret the second picture as the SVA1032X required a full 110 minutes to fully settle with a constant 23ºC ambient temperature (which is a whole lot longer than I ever imagined it would take).The reason the traces start relatively flat and get worse over time is that the recalled ecal had been performed another day on a completely cold turkey instrument (within 2-3 minutes of starting equipment). This time I took advantage of the warm instrument and did another eCal at 125 minutes and saved it for good later use. Traces look flat as they should with the warm ecal.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 04, 2025, 07:28:58 am
content: The vast majority of the time, those errors would not be big enough to cause me any concern.Attached photo is data from the low cost LiteVNA comparing the S21 from a cold start to after 24 hours of operation. Below 1GHz it's very stable.