20dB 'RF' attenuator - seeking feedback to improve - Page 1
Forum section: electronics / projects

author: enut11
author_rank: Super Contributor
timestamp: February 02, 2020, 02:28:33 am
content: My first 50 ohm 'RF' attenuator built on a 25x65 double-sided pcb.20dB attenuation using metal film resistors.As far as I can measure, it is -1.5dB at 45MHz.I would like to do better than this and get to about 300MHz.Is this possible using conventional axial resistors.Suggestions?enut11

author: awallin
author_rank: Frequent Contributor
timestamp: February 02, 2020, 08:24:54 am
content: build the same thing with SMD and SMA-connectors and compare?something like that:https://www.banggood.com/DC-4_0GHz-RF-Fixed-Attenuator-Radio-Frequency-Fixed-p-1119478.htmla grounded metal box around everything (aluminium foil in the prototyping-stage?) might help.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 02, 2020, 09:05:12 am
content: Well don't fly it in air, put those puppies down on the ground plane!Also use connectors that aren't two teeny wires. Those things are dumb, they shouldn't exist.An edge-launch or 5-pin style will do alright.You may still need to use wider or flatter (or more in parallel?) resistors to keep Zo right, or use SMT chip resistors which, obviously, don't stand up at all, they stay flat to the plane. Carve a trace across the board so you get a microstrip or coplanar waveguide geometry.Tim

author: ebastler
author_rank: Super Contributor
timestamp: February 02, 2020, 09:37:37 am
content: Here's a short video that demonstrates a more compact style of building these, with better HF properties. A bit of theory first; then he shows his homebrew build starting around 6:30:

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: February 02, 2020, 09:43:06 am
content: Free air impedance of 50mm of 0.5mm wire is +j*14.1Ohms at 45MHzhttps://chemandy.com/calculators/round-wire-impedance-calculator.htmI think that's the main killer of this construction style.Leo

author: enut11
author_rank: Super Contributor
timestamp: February 02, 2020, 09:54:20 am
content: Quote from: Leo Bodnar on February 02, 2020, 09:43:06 amThanks Leo Bodnar. That's what I needed to know.I want to avoid SMA if possible as it involves too many adapters. Ditto wrt surface mount but may revisit this later.I will start by lifting the ground plane up to the series resistors and see what improvement that offers.enut11

author: duak
author_rank: Super Contributor
timestamp: February 02, 2020, 07:23:23 pm
content: Others have covered rebuilding with the resistors closer to the ground plane.Two resistors in parallel will give twice the parasitic parallel capacitance of a single resistor. It'd be better to use two in series if you can't get the exact value needed.A trimmer capacitor across the central resistor could compensate for the parasitic capacitance of the resistors. If you model the circuit including the parasitic capacitances, I think you'll find a compensation cap is needed for VHF. Passive scope probes have these. The central resistor to ground will have an inherent series inductance caused by the loop area. If significant, two resistors in parallel but arranged in opposite directions like a '+' can help.I built a filter in a similar case. Adding a grounded metal divider with the signal passing through a hole helped ultimate rejection. I'd consider an upside down U shaped one to shield the central node. The series resistors would pass through the two holes in the divider. However, if the ground plane can be brought up to the resistors, a grounded shield can be placed on top making a sandwich of it and no holes would be needed.Cheers,

author: enut11
author_rank: Super Contributor
timestamp: February 03, 2020, 02:55:37 am
content: Thanks @duak. Lots to consider for my next upgrade.Meanwhile, have a look at my latest mods, done before I read your posting.Yet to be tested as I need a reliable HF generator (current one max is 50MHz).The resistor network now sits on a grounded plane with shortened input/output leads poking through grounded shields.Maybe a pi configuration would be better if I must use series resistors?enut11

author: David Hess
author_rank: Super Contributor
timestamp: February 03, 2020, 04:41:49 am
content: Axial resistors like that in a cavity are good to 1 GHz so hug the ground plane. Use a connector which terminates closer to the ground plane like edge mount. Through-hole 1/8 watt parts are smaller and will perform a little better. Mount the shunt resistors to make a cross along the ground plane instead of a tee.

author: enut11
author_rank: Super Contributor
timestamp: February 03, 2020, 05:46:50 am
content: Quote from: David Hess on February 03, 2020, 04:41:49 amThanks David. The shunt resistor is 10 ohm for the T-attenuator.If I use 18 ohm and 22 ohm in parallel I can form a cross arrangement of resistors. 18//22=9.9 ohmThe cross arrangement was also suggested by @duak.enut11

author: Miti
author_rank: Super Contributor
timestamp: February 03, 2020, 12:15:18 pm
content: Quote from: enut11 on February 02, 2020, 02:28:33 amhttps://www.minicircuits.com/WebStore/dashboard.html?model=HAT-20%2B

author: EEEnthusiast
author_rank: Frequent Contributor
timestamp: February 03, 2020, 12:33:27 pm
content: I have made tons of those attenuators. The layout is the key in all of these.Few tips1. Use the smallest possible resistor case size (0402 or 0201 if you can solder them)2. Use micro-strip to route the signal in and signal out.3. Use end launch SMA connector for the ends.4. Match the width of the trace to the width of the component. For e.g. in case of 0402 , use a trace width of 20 mils5. Adjust the ground plane height in order to get 50 Ohms at 20 mils width.6. Use a PI or T network. The shunt element should have its pad resting on the transmission line so that there is no stub.7. For the ground connection, use multiple vias to connect to the ground plane below.If you do all these, and with enough luck you may be able to get an flat attenuator well into couple of GHz.

author: cncjerry
author_rank: Unknown
timestamp: February 03, 2020, 07:12:36 pm
content: There are/were smd boards unpopulated on ebay for attenuators and filters. They used sma edge connectors and the circuit board lines were 50ohm. I bought some. Then I found these little screw on attenuators that were really nice for such low cost I gave up making my own. The nice thing about making your own though is if you burn them up, they are cheap to fix.

author: enut11
author_rank: Super Contributor
timestamp: February 03, 2020, 08:54:56 pm
content: AllThanks for all the suggestions. And yes, I could buy a 20dB attenuator for a few dollars but there is little to learn in doing thatOne thing that I have noticed is that members prefer SMA to BNC. Can anyone explain this given that most test gear is fitted with BNC?enut11PSAt the moment the max I can test at is 50MHz and even that is probably a little dodgy. Any suggestions for an affordable 500MHz or 1GHz generator?

author: Miti
author_rank: Super Contributor
timestamp: February 03, 2020, 10:44:29 pm
content: Any respectable test instrument that goes into GHz is fitted with N type connector. BNC was designed, according to Wikipedia, for applications up to 2GHz but I wouldn’t use it in a test system that goes close to that frequency. SMA can go up to 18GHz. I use SMA and SMA to N adapters in most of my test equipment.

author: ogden
author_rank: Super Contributor
timestamp: February 03, 2020, 11:33:33 pm
content: Quote from: enut11 on February 03, 2020, 08:54:56 pmYou may consider NanoVNA. Not quite generator, but next best thing to measure your attenuators. Far from "lab grade instrument", yet gives surprisingly good results up-to 300MHz and with (quite) some compromises up-to 900MHz.

author: enut11
author_rank: Super Contributor
timestamp: February 04, 2020, 02:17:07 am
content: Quote from: EEEnthusiast on February 03, 2020, 12:33:27 pmThanks EEenthusiastI cut my (electronic) teeth on audio and analog power supplies. RF is new learning for me.1) So one must sacrifice power handling for frequency performance by using smaller resistors?2) Not familiar with 'microstrip' but will do a search.3) Looks like I will have to succumb to SMA on the next design. However, If I use adapters to connect to my BNC equipment, it seems I will not be gaining much??4), 5) and 6) : RF track layout is outside my current knowledge so will have to research.7) Easy to implimentenut11

author: EEEnthusiast
author_rank: Frequent Contributor
timestamp: February 04, 2020, 03:56:10 am
content: Microstrip is nothing but a simple trace with a complete ground plane below it. You can search for online calculators, which will calculate the width of the trace needed for your dielectric.What kind of power are you planning to dissipate. For higher power dissipation, you could use multiple resistors in series parallel combination.For a 20dB attenuator, you make it into multiple stages. For eg. 10 stages of 2dB each. So each stage will dissipate less power.

author: EEEnthusiast
author_rank: Frequent Contributor
timestamp: February 04, 2020, 04:04:45 am
content: Your final PCB will look like multiple PI or T sections cascaded in series.Something like this...

author: enut11
author_rank: Super Contributor
timestamp: February 04, 2020, 04:47:12 am
content: Quote from: EEEnthusiast on February 04, 2020, 03:56:10 amAt this point in time I do not have a particular 'power' application and am just learning 'RF' methodology.I have been characterising my instruments (HF voltmeter and DSO) and need to reduce the signal for the lower ranges (power requirement is very low).For the attenuator circuit board layout you say that a strip of a certain width is needed to suit the ground plane I am using (1.5mm double sided copper fiberglass PCB). Does this mean it can only be used over a small frequency range?enut11

author: Berni
author_rank: Super Contributor
timestamp: February 04, 2020, 06:44:04 am
content: Quote from: enut11 on February 03, 2020, 08:54:56 pmBecause SMA is a better connector in a lot of ways and is very common everywhere.The BNC connector while very common has some issues. While it is very easy to plug in (No need to screw it on all the way) it does suffer in terms of RF performance and is physically pretty large. Have a look at RF test equipment and try to find a BNC on there, you won't. What you find there is N connectors or sometimes APC7 connectors (Mostly only on network analyzers) because of there much superior RF performance. Any BNCs you find on RF test gear is for slow low bandwidth signals like modulation, leveling control, gating, trigger etc..In general typical BNC starts having problems once you approach 1GHz, fancy good quality BNCs go higher into a few GHz but you also need the nice high quality connector on the cable too. While the N connector has no problems with GHz and good ones go to 20GHz and up. Only problem is that N is twice the size of BNC so soldering N connectors on your deadbug style prototype circuit is not convenient at all. However there is also the popular SMA connector, featuring a size significantly smaller than BNC while offering good RF performance to 4GHz for the cheap ones while higher performance variants like the 3.5mm or 2.5mm go beyond 20GHz in the identical form factor (Even SMA compatible, but please be nice to fancy RF connectors). You can buy a bunch of cheep board mount SMA connectors and just solder then into your circuit whenever needed, treat them as disposable.Have a look at one of the biggest manufacturers of RF modules:https://www.minicircuits.com/Most of there modules are SMA because its such a convenient connector that provides great RF performance in a small form factor.But... my <insert testgear here> only has BNC!Well.. so? What does it matter? You do need a cable to hook it up to something anyway. So you just get a cable that is BNC on one end and SMA on the other. Any place that sells RF cables will have such cables. Or if you want to DIY it you can just cut up a BNC cable in half and put SMA connectors on the end yourself. So i just keep a bunch of BNC to SMA and N to SMA cables and a box full of cheep various kinds of board mount SMAs.If you want cheap cables but want it a bit more legit than a random ebay seller this is a good Chinese company:https://www.rfsupplier.comThey have every possible RF connector and will make any kind of custom RF cable for you even in small quantities.As for a RF generator, used market like ebay is the best choice to pick up an old boatanchor that goes to a few GHz (Tho australia might be tricky)Also if you are just getting into RF maybe you might find the NanoVNA very useful:http://nanovna.com/Its a $50 network analyzer to 900 MHz (Tho best performance is only up to 300MHz). This lets you characterize your RF blocks properly across frequency and show you things like phase and return loss.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 04, 2020, 01:26:46 pm
content: Quote from: enut11 on February 03, 2020, 08:54:56 pmSeeing that you are experimenting, you may want try different resistor types as well. You may also want to try using a Pi arrangement as well.I agree with the above comment about buying the NanoVNA as a starting point. Looking at your 20dB example wouldn't be a problem with it. Even at 1GHz, I imagine you would at least be in the ballpark with it.https://youtu.be/mKi6s3WvBAM?t=2021

author: David Hess
author_rank: Super Contributor
timestamp: February 04, 2020, 04:50:22 pm
content: Quote from: Miti on February 03, 2020, 10:44:29 pmFor a while there was push to replace BNC connectors with SMB connectors in test instruments.Quote from: enut11 on February 04, 2020, 02:17:07 amAt higher power and frequency, transmission line construction would be used for the resistors so that they could be made much larger.On a more practical level, multiple attenuator sections made from discrete parts can be used in series to distribute the heat. So for example stacking 3dB, 14dB, and 3dB sections will double the power over a single 20dB section because the first stage only absorbs half of the power. Other circuit layouts are possible to increase power handling.Quote from: Berni on February 04, 2020, 06:44:04 amTektronix discovered that when designing their 7A29 1 GHz vertical amplifier for their 7104 1 GHz oscilloscope mainframe. No available BNC connector at the time had a uniform impedance so Tektronix ended up making their own precision BNC connectors.

author: ogden
author_rank: Super Contributor
timestamp: February 04, 2020, 05:14:49 pm
content: Just equip all your equipment with SMA adapters, use SMA cables. I don't even reuse "made in China" low cost SMA PCB connectors, just throw used testboard in the "afterlife box" as it is. You get bag of 100 edge SMA sockets for10$20$. Try this with BNC.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 04, 2020, 07:58:26 pm
content: Test using the Nano, sweeping to 1GHz.IMG_4453, test setupNano_thru, showing the thruNano_MWM20dB, DC-18GH MidWest...Also for fun, showing the MidWest's gain on my 1970's HP8754A sweeping to 1.3GHz. Also shown is the surface mount attenuator. Normally we would look at more than gain but I think this should give you some idea what to expect.The Nano is a really nice tool for getting started with RF.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 05, 2020, 04:16:52 am
content: I have the 3GHz test set for the 8754A and a Mini-Circuits doubler that allows the system to reach a little over 2.6GHz.In the graphs the blue is phase and red is the gain.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 05, 2020, 04:49:44 am
content: In these plots I have changed it to 1dB/div and compared the homemade surface mount against the Midwest part.The 8754A has basically no intelligence and there is no way for the software to know how the instrument is setup so the software doesn't rescale the graphs like with the Nano. To make this measurement, the thumb wheel switch is changed to give it a 20dB offset.If you wanted to look at say a 50dB attenuator with the Nano at a GHz, you will be out of luck. The Nano doesn't have a lot of dynamic range and is pretty noisy, but it's $50 so it's pretty hard for me to fault it. The Nano V2 is supposed to be available soon. This may be a better system for the hobbyist.

author: enut11
author_rank: Super Contributor
timestamp: February 05, 2020, 07:22:21 am
content: Quote from: ogden on February 03, 2020, 11:33:33 pmThanks @ogden (and @ Berni). I have purchased a NanoVNA online from a local Sydney dealer. He claims to sell the genuine model. Apparently there are [inferior?] clones available on eBay.I will also bow to the collective wisdom of Forum members and order some SMA edge connectors and cables.Thanks to all who have taken the time to reply to my request. This Forum is the place to gain rapid knowledge.

author: enut11
author_rank: Super Contributor
timestamp: February 05, 2020, 07:36:16 am
content: Quote from: joeqsmith on February 04, 2020, 07:58:26 pmThanks @joeqsmith. Lots to read and absorb in your post.Very impressive set of test gear! BTW, I just found your Youtube review on the NanoVNA. Thanks for that.Where did you get those small PCBs with the the SMA connectors. Looks like what I need to build my next 20dB attenuator.enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: February 05, 2020, 06:30:58 pm
content: Quote from: enut11 on February 05, 2020, 07:36:16 amThose are a custom PCB but I have to believe you could find something stock by now.I think you will be impressed with the Nano's performance and what it can tell you about your circuits.I would like to get something a newer that can be controlled similar to the Nano, and make some sort of comparison video between the NanoVNA, the Nano V2, the HP relic and what ever I end up with to replace it.

author: ogden
author_rank: Super Contributor
timestamp: February 05, 2020, 08:43:27 pm
content: Quote from: joeqsmith on February 05, 2020, 06:30:58 pmSuch a simple layout can be made from double sided CC PCB using exacto knife or dremel or nail lacquer + etch_solution in comparably short time.

author: fourfathom
author_rank: Super Contributor
timestamp: February 06, 2020, 12:26:59 am
content: Quote from: ogden on February 05, 2020, 08:43:27 pmI sometimes make boards like this using a small woodworking v-gouge to cut between the copper traces. Use a thick steel straight-edge to guide the gouge and be sure to cut *away* from your fingers. Or just freehand it, but do be careful.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 06, 2020, 01:07:12 am
content: I put together a 50dB attenuator using 0603s & 1206s built on the same section of microstrip. I set the Nano to sweep to 1.5GHz and installed a Midwest Microwave 18GHz, 10dB attenuator. I then installed the home made attenuator. +/-25dB isn't very good but is it my circuit or is it the nano. It's easy to measure 10dB but 50dB may be pushing the $50 pocket unit.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 06, 2020, 01:20:27 am
content: The old HP8754A is a bit odd in that it uses eight vertical divisions rather than the typical 10. To measure down this low, I need to add a 40dB offset to make the top line 0dB. The doubler is still installed and the instrument is sweeping to 2.6GHz.Installing the Midwest Microwave 10dB attenuator, we can see it is one division down or 10dB and is basically flat, as we would expect.Now let's have a look at our home made 50dB attenuator. I suspect the old HP is going to be much closer to reality than the Nano but it's only $50 and for that, a great learning tool.

author: Berni
author_rank: Super Contributor
timestamp: February 06, 2020, 06:14:29 am
content: 50dB attenuators do get a lot trickier.The resistor values start getting very far from 50 Ohm so the parasitics of those resistors become much more visible. But also leakage can be a problem.I did make one once when i needed a high value attenuator i didn't have on hand and ended up making it on the PCB as 3 stages of attenuators in series so that each one didn't have do do quite as much attenution. Giving it shielding made from thin sheet metal also improved the response since at these low levels any sort of leakage can be seen making its way across. Still was not quite all that flat tho so i suggest against DIYing attenuators this strong if you want it ruler flat.A nice thing that is easy to DIY however is a resistive 3 way power splitter/combiner. Made one by soldering 3 SMAs into a triangle and joining then together in the middle with a star configuration of the right value 0402 SMD resistors. It seamed to work great from DC to 3GHz (Didn't have gear to measure higher).

author: joeqsmith
author_rank: Super Contributor
timestamp: February 06, 2020, 03:24:07 pm
content: Quote from: Berni on February 06, 2020, 06:14:29 amGood points. My 50dB example used two stages (lazy) which is really pushing things. My goal was more to show the differences between the Nano and my old HP VNA as we start working with lower signal levels.Op, you may be interested in the following article on construction. It's very short and provides some practical information.https://www.electronics-notes.com/articles/radio/rf-attenuators/construction-practical-tips-guidelines.phpI'll try to make something a little better using a PI type and more stages and compare it against a commercial grade part.

author: ogden
author_rank: Super Contributor
timestamp: February 06, 2020, 03:53:50 pm
content: Quote from: joeqsmith on February 06, 2020, 03:24:07 pmWhen you challenge noise floor of instrument, you better demonstrate it. Now it is impossible to know - poor isolation results are due to leakage through attenuator or instrument (NanoVNA) itself. Yes, we see better results with HP VNA, yet showing "open" S21 curve of your NanoVNA would be much more telling and educational.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 06, 2020, 07:00:36 pm
content: PIC1Three stage PI configuration made with 0603 & 1206 parts, with shield.PIC2The S-parameter test set on the 8754A includes a 70dB step attenuator (manual of course). This was set to 50dB and a thru was installed. As previously, thumb wheel switches set for a 40dB offset. The top of the graph is 0dB. Gain is 50dB.PIC3The internal step attenuator was set to 0 and the thru was replaced with a JFW attenuator.PIC4The home made three stage attenuator was installed. At this time, no shielding was added. Maybe 42dB at 2.6GHz.PIC5A simple shield was added. Maybe 45dB at 2.6GHz. A noticeable improvement.PIC6The shielded attenuator on the NANO, sweeping to 1.5GHz.It appears to be a significant improvement in the flatness compared with the 2-stage one. Shouldn't be too surprising.

author: enut11
author_rank: Super Contributor
timestamp: February 06, 2020, 09:13:34 pm
content: Quote from: joeqsmith on February 06, 2020, 03:24:07 pmThanks. That is a good introduction to RF and attenuators.enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: February 07, 2020, 02:23:11 am
content: Glad to help. Another pretty good resource is the ARRL Handbook. Even the very old editions may be helpful. They used to have a good section on construction practices.Just for fun, I made one last attenuator. This time it's a 4-state T. I set the 8754A to sweep to 200MHz. One plot is 10dB/div, the other 1dB. You can see a slight rise to it. I then set the Nano to also sweep to 200Mhz. You can see the two systems are fairly close when looking at the lower frequencies.Good luck with your projects. Let us know how you like the Nano after you have played with it for a while.

author: enut11
author_rank: Super Contributor
timestamp: February 07, 2020, 07:26:11 am
content: Hi @joeqsmith, @ogden and @BerniThe NanoVNA arrived today. Quick delivery from Sydney. Just connected it to the PC to charge the battery.Switched it on and found it a little daunting!I admit that I am out of my depth at the moment.Looking around for PC interface software and any other info to soften the learning.From what I have read so far, my next (SMA based) 20dB attenuator is better be done in stages, say 10dB +10dB.Is there anything to choose between T and Pi arrangement of resistors?enut11

author: ogden
author_rank: Super Contributor
timestamp: February 07, 2020, 08:48:03 am
content: Few cents: in pictures from @joeqsmith we see PCB edge-mount male connectors, male-female cables. That is very unusual approach - due to surplus/scrap/misordering(?). Better & widespread approach: female SMA receptacles on instruments/boards/devices and male-male SMA cables. Only case when you would want to use PCB edge-mount SMA male+female connectors would be small RF accessories like: attenuator, DC block, Bias tee and (maybe) LNA.

author: tkamiya
author_rank: Super Contributor
timestamp: February 07, 2020, 02:47:26 pm
content: I just wanted to say:Getting certain attenuation value is relatively easy but getting flatness across wide range is half art, half science. HP attenuators for example, uses copper "flaps" to purposely generate stray capacitance and they are hand tuned. Also, registers like that aren't inductance free. Often carbon/metal coating on ceramic core is cut in spiral to establish values.Also, OP's construction has way too much stray inductance and capacitance. I don't think suspending resisters in air is bad thing but choice of connectors are not optimum. If BNC, center conductor attach point should be much shorter, and I don't mean resister leads. Internal to that connector is a long enough lead wire between gold plated brass center pin and where it comes out of the metal shell.Argh.... I should stop reading every post on EEVBLOG! Now I want to replicate this experiment myself and see how I do!

author: joeqsmith
author_rank: Super Contributor
timestamp: February 07, 2020, 07:30:02 pm
content: Quote from: tkamiya on February 07, 2020, 02:47:26 pmNormally I turn to foil tape and razor blades or magnet wire stubs to trim them. Shown is a small load with a tap that I wanted some decent flatness.https://www.eevblog.com/forum/projects/home-made-pa-and-load/msg635851/#msg635851I modified a cheap DC current clamp a while back to increase it's bandwidth. That thing was a nightmare to get a decent response out of and I was only running at a 100KHz or so.

author: tkamiya
author_rank: Super Contributor
timestamp: February 07, 2020, 07:34:29 pm
content: Very nice, indeed!

author: ogden
author_rank: Super Contributor
timestamp: February 08, 2020, 10:36:54 pm
content: Accidentally stumbled on this $1.33 (+0.88$) set of attenuators. I doubt it can reach 4GHz, but whatever:https://www.aliexpress.com/item/4000333427604.html

author: joeqsmith
author_rank: Super Contributor
timestamp: February 08, 2020, 10:43:10 pm
content: This is the 4-stage T attenuator after a few mods. There are 18 resistors on the board with a layer of Kapton, then some copper foil strips that I trimmed very carefully. It's well within a half dB up to 1.5GHz.

author: EEEnthusiast
author_rank: Frequent Contributor
timestamp: February 09, 2020, 02:24:34 am
content: Quote from: ogden on February 08, 2020, 10:36:54 pmHow can these guys sell them for $1.33 with 8 of those SMA connectors.

author: tkamiya
author_rank: Super Contributor
timestamp: February 09, 2020, 04:00:00 am
content: I have a many cheap Chinese made no-brand-name SMA connectors. The "Gold" plating is so thin if I attach anything and remove it, metal underneath will show. Then it will start to turn black and corrode. I don't think plating is actually gold.That attenuator is cheap even by China's standard. I have to wonder what's going on....

author: joeqsmith
author_rank: Super Contributor
timestamp: February 09, 2020, 04:30:28 am
content: It seems they are on eBay and Amazon for about 5$-$15 USD. Maybe someone will test what you get for your cash... I would expect its like a Chinese 1000V CAT IV meter with glass fuses or a 5000mAh 9V transistor battery.My home made ones are good to 8GHz.https://www.ebay.com/itm/DC-4-0GHz-23dBm-RF-Fixed-Attenuator-SMA-Double-Female-Head-0dB-10dB-20dB-30dB/174018514007?hash=item28844fcc57:g:qwkAAOSwBbBdbshDA different stylehttps://www.ebay.com/itm/23dBm-DC-4-0GHz-RF-Fixed-Attenuator-SMA-Double-Female-Head-0dB-10dB-20dB-30dB/173343871488?hash=item285c199200:g:8q8AAOSw7m9bEB9s******Just looked at the second ad. So 30dB with a flatness of 1.5dB up to 4GHz.Direct: 0dB (reference)Level 1: 10 0.8 dBLevel 2: 20 1.1 dBLevel 3: 30 1.5dB*****And ... Standing wave ratio: 1.20Made another attempt to bring it in tighter. Within 0.2dB. Here is the gain and SWR.

author: enut11
author_rank: Super Contributor
timestamp: February 09, 2020, 04:36:52 am
content: Quote from: joeqsmith on February 08, 2020, 10:43:10 pm@joeqsmith, very impressive. Can you post a picture of the pcb?enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: February 09, 2020, 05:25:58 am
content: Quote from: enut11 on February 09, 2020, 04:36:52 amI looked to see if I had taken a clearer picture before I started adding the tape and foil to it. This was cleanest one I found. Just a bunch of resistors.How's that Nano coming along? Did you join the IOGroups? I understand there is now a fair amount of information there that may help you get started.

author: ogden
author_rank: Super Contributor
timestamp: February 09, 2020, 08:59:45 am
content: Quote from: tkamiya on February 09, 2020, 04:00:00 amMine do not corrode, yet plating flake off easily and contaminate connectors. So I have different sets of cables and accessories - for flaky SMA and quality (H&S) SMA

author: Calvin
author_rank: Regular Contributor
timestamp: February 09, 2020, 09:27:10 am
content: Hi,these relatively cheap Rs might do quite well especially those in the 50-100R rangeMMA0204AC5009FB300 (0,184€@100pcs at Mouser)regardsCalvin

author: ogden
author_rank: Super Contributor
timestamp: February 09, 2020, 11:02:04 am
content: Quote from: Calvin on February 09, 2020, 09:27:10 amIt is 0,184€/piece @100pcsThat is *very* expensive 0204 resistor.

author: Calvin
author_rank: Regular Contributor
timestamp: February 09, 2020, 11:29:16 am
content: hi,well then .... which ´cheaper´ RF-resistor could You suggest?regardsCalvin

author: ogden
author_rank: Super Contributor
timestamp: February 09, 2020, 11:57:38 am
content: Quote from: Calvin on February 09, 2020, 11:29:16 amThere is huge difference between "cheap resistors" and "cheap RF resistors". I fail to find any mention of "RF" in your initial post.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 09, 2020, 05:09:39 pm
content: Quote from: Calvin on February 09, 2020, 09:27:10 amhttps://www.mouser.com/datasheet/2/427/mmu0102mma0204mmb0207hf-465485.pdfLooks like digikey offers a kit.https://www.digikey.com/product-detail/en/vishay-thin-film/764-1558-KIT/764-1558-KIT-ND/7313792For my home projects, I've had decent results using standard resistors up to a GHz or so. I played around a bit at higher frequencies but I would say I was chasing my tail at best as I just didn't have the tools. I used some commercial mixers, YIG and coupler to push the Nano above 3GHz, but no way to calibrate it with any sort of confidence.Years ago during a visit to the Dayton Ham show, someone was selling Narda terminators for a couple of bucks or so each. I picked up a few in hopes I could use them to make a decent SOL standard set for my higher frequency experiments. These can be taken apart. Using a lathe and some Teflon, I made up some new internals for the open and and copper for the short. The parts were phase matched on the old VNA. Still, the software I wrote for the old VNA is light years better than using a grease pen, it is no where near what a modern VNA would have in terms of calibration. It assumes the SOLT is perfect which it obviously is not.Then again, it's just a hobby.

author: enut11
author_rank: Super Contributor
timestamp: February 09, 2020, 06:57:42 pm
content: Quote from: joeqsmith on February 09, 2020, 05:25:58 am@joeqsmith, Still playing with the NanoVNA when opportunity arises.Will join an IOgroup when I feel I can ask intelligent questions.At the moment I need to come to grips with RF fundamentals.I found some PC interface software called nanovna-saver-v0.2.2 which seems to be OK.I also purchased some more cable and connectors online. Now I am finding out that connector quality may be an issue.If you have a reliable online source for SMA I would appreciate the info.enut11

author: ogden
author_rank: Super Contributor
timestamp: February 09, 2020, 07:08:08 pm
content: Quote from: enut11 on February 09, 2020, 06:57:42 pmmouser.com They are official distributor of Huber+Suhner

author: joeqsmith
author_rank: Super Contributor
timestamp: February 09, 2020, 08:13:04 pm
content: I pretty much stay with Amphenol, Johnson or Molex lower end parts from Digi-key. For the VNA, I use RG400/U, which is far from ideal. Start pricing some decent cables and you may be in for sticker shock.I expect a single Gore flex cable would cost more than my old HP VNA with cables cost.https://www.gore.com/products/gore-vna-microwave-rf-test-assembliesThe following paper from HP talks about the various connector grades. I don't think this covers the $0.50 connectors we are seeing from China.http://na.support.keysight.com/pna/connectorcare/Connector_Grades.htmIf you are just playing around and learning the basics, using the really cheap parts shouldn't be much of a problem. Just consider them disposable. If you stay interested in RF design, you can invest in better parts, cables and TE.Article on connector care. Things you want to learn before you buy good connectors.https://www.microwaves101.com/encyclopedias/connector-careI have not tried the Nanovna saver software but see people post about it from time to time. It sounds like they have done a really nice job with it.

author: Berni
author_rank: Super Contributor
timestamp: February 10, 2020, 07:11:20 am
content: Id say don't get any fancy RF connectors unless you have a good reason to.If you have a NanoVNA or a really old network analyzer that only goes to 1GHz any cheep SMA connector will do fine. As long as its not actually out of spec (Ocasonaly chinese crappy connectors are that bad).If all your connectors are crap to begin with then there is no danger of damaging them. Just use a quality SMA to N adapter on the network analyzer or whatever so that if you wreck the SMA connector you can just replace the adapter.Its only when you go above 4GHz or start measuring really low down return losses is where you need the fancy Gore brand cables that cost an arm and a leg. So given how much they cost you really want to take care of them

author: enut11
author_rank: Super Contributor
timestamp: February 10, 2020, 09:15:24 am
content: @joeqsmithIn your picture showing the NanoVNA with some attenuators, on the 20dB ones using discrete pigtail resistors, is there a copper pad under the junction of the resistors?If so, what is the size of the gap in the central copper strip before and after this pad.enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: February 10, 2020, 01:25:55 pm
content: Quote from: enut11 on February 10, 2020, 09:15:24 amYes, there is a pad there. These boards are used to test components on the VNA and to remove the effects of the connectors and such (de-embed). This particular board is the thru which I have taken a razor blade to. If you are interested in laying out boards, you could use a free program like AppCAD to get an idea what dimensions you need.The number of mate cycles you will get out of the really cheap connectors may not be very good. You may want to inspect them for any sort of burrs or debris before using them.A few articles on cables:https://www.microwaves101.com/encyclopedias/cable-carehttps://www.tek.com/blog/improving-vna-measurement-accuracy-quality-cables-and-adapters

author: enut11
author_rank: Super Contributor
timestamp: February 10, 2020, 07:12:40 pm
content: @joeqsmith, what I wanted to know is how much of that central strip did you cut away before and after the pad at the junction of the resistors?thanksenut11

author: enut11
author_rank: Super Contributor
timestamp: February 10, 2020, 09:56:33 pm
content: @joeqsmithI played around with the APPcad numbers for my 1.5mm double sided circuit board until I got 50 ohms.What I do not know is the 'FR' value (dielectric) for my PCB so I assumed a mid-range figure of 4.6Ended up with a 2.8mm central strip with 2.5mm gaps either side. Looks OK?enut11

author: enut11
author_rank: Super Contributor
timestamp: February 10, 2020, 10:38:29 pm
content: Quote from: joeqsmith on February 10, 2020, 01:25:55 pmYikes! What a minefield cables can be. May be better off sticking to the lower HF area for the time being...

author: joeqsmith
author_rank: Super Contributor
timestamp: February 11, 2020, 01:03:05 am
content: Quote from: enut11 on February 10, 2020, 07:12:40 pmAgain, I'm using a razor blade so it's not exact. Basically, I used the length of the axial body. In hindsight, using a smaller gap may have helped improve the performance by adding a little more capacitance. Then again, maybe a little foil and some tape.... You may notice the gap is similar on the 0603 parts. It's certainly not optimum but as you can see, it can yield some decent results at lower frequencies.I have ordered a few of the low cost attenuators. These may be a good starting point for your experiments.Quote from: enut11 on February 10, 2020, 09:56:33 pmAt lower frequencies, the software should do fine but I doubt you would want to pay to have a PCB made from better materials and controlled impedances. I would check with your board house before you settle on a design. Maybe even try a couple of different dimensions to hedge your chances.Quote from: enut11 on February 10, 2020, 10:38:29 pmI've had a lot of fun playing with RF without having to resort to anything too crazy. There's no reason you can't use the Nano to experiment in the GHz range. I would like to see the Nano V2 3GHz unit. If you can believe the internet, they are now working towards 6GHz. That will be impressive.

author: enut11
author_rank: Super Contributor
timestamp: February 11, 2020, 01:41:53 am
content: Is the V2 a larger screen for around x2 the price?

author: joeqsmith
author_rank: Super Contributor
timestamp: February 11, 2020, 03:09:42 am
content: From the little bit I have seen, I thought it was a 3GHz version that doesn't use harmonics. I've seen some posts about it going to 3.5. I wouldn't count on anything until they start shipping and we can have a look.

author: enut11
author_rank: Super Contributor
timestamp: February 13, 2020, 02:44:34 am
content: While waiting for my SMA connectors and adapters to arrive I started playing around with a hand-carved PCB (using my old BNC connectors) and a star arrangement of resistors.The paralleled series resistors are 82 ohm each. Attenuation is 20dB.Question: When paralleling resistors, is it better to separate them (as I have) or to mount them close against each other?enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: February 13, 2020, 02:59:19 am
content: What's that one look like on the Nano if you sweep to 40MHz, compared with your first one? Take a few pictures of the Nano's screen if you don't have the software working yet.

author: enut11
author_rank: Super Contributor
timestamp: February 13, 2020, 03:20:05 am
content: Hi joeqsmithNo way to check any of my attenuators on the NanoVNA until I get my SMA bits and pieces.I did check with my DSO and it is slightly better compared with the original attenuator up to 50MHz.My DSO is -3dB at 170MHz.enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: February 13, 2020, 11:58:04 am
content: Quote from: enut11 on February 13, 2020, 03:20:05 amQuoteI had assumed that you meant it was 20dB minus the 1.5 or 18.5dB at 45MHz and the new one is now 17dB at 170MHz. But maybe you are actually reading 3dB at 170MHz. If it really is this far off, I wonder how you validated your setup using the scope. Are your scope and source both 50 ohms? If you use a cable to connect the two, is it flat? If not, are you accounting for this error in your measurements?It will be interesting to see how your results compare when you place the same attenuators on your Nano.

author: duak
author_rank: Super Contributor
timestamp: February 14, 2020, 01:43:49 am
content: I don't think the spacing between the paralled resistors matters too much but I expect closer to be better.The cutout in the ground plane concerns me. i think I see a significan loop area because of the cutout. What happens when you lay a ground plane on top of the circuit? Make sure there are at least four connections to the existing ground plane and that it is as close as possible to the resistors without shorting them out. i use really thin one side copper FRP for test shielding.Also, are your test cables in good shape? Maybe the shielding braids and connections are not solid and the attenuator is being bypassed by leakage between the input and output cables.Cheers,

author: enut11
author_rank: Super Contributor
timestamp: February 14, 2020, 09:20:27 pm
content: @duakShould the input, output and center pads for the resistors just be islands on an otherwise continuous ground plane? This seems to go against what I have seen so far in this thread??I will try an upper ground plane later but I do not have the means to test it properly until my NanoVNA adapters and leads arrive.Cables? Currently cheap Chinese BNC on RG58 along with in-line 50 ohm BNC loads.enut11@joeqsmiithI was not very clear in my reply about testing the latest attenuator.I set up my Wavetek Model 80 to output 50MHz at 1V and compared the output of my 2 attenuators on my DST1102B DSO.There is not enough evidence at this time to draw any conclusions.enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: February 15, 2020, 02:56:49 am
content: Quote from: enut11 on February 14, 2020, 09:20:27 pmI think we have an answer to your problem. That attenuator is meant to drive into 50 ohms where your scope appears to not support it. You would need to add and external 50 ohm terminator. Something like these:https://www.amazon.com/Copper-Adapter-38-5mm-Through-Terminator/dp/B07G566JC7/ref=pd_sbs_23_t_1/131-1485153-0357844?_encoding=UTF8&pd_rd_i=B07G566JC7&pd_rd_r=d6af2da5-ac8f-46c0-b283-2f19c2d95aad&pd_rd_w=h3Kiw&pd_rd_wg=Cdwgs&pf_rd_p=5cfcfe89-300f-47d2-b1ad-a4e27203a02a&pf_rd_r=JA7B155VSYWS2A3KXGYC&psc=1&refRID=JA7B155VSYWS2A3KXGYCAfter you get the termination correct, you should see your 10:1 divider.I repeated your test. I ran the RF generator into a splitter. One port goes to directly to the scope, the other through the attenuator then to the scope. Even with the three resistor T, you can see at 50MHz, I am very close to 10:1. One thing to keep in mind is your want to make sure your scope is working in a linear region.With the Nano, you are already working with a 50 ohm system so you can just measure it directly.Hope this helps.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 15, 2020, 03:12:18 am
content: Same setup, at 300MHz.

author: duak
author_rank: Super Contributor
timestamp: February 15, 2020, 08:39:30 pm
content: Enut11 - yes, a mostly solid ground plane tying all the signal common points together is best. There can be cutouts for circuit nodes but otherwise it should be solid.The way I visualize it, the ground plane does at least two things: it ties all the signal common points together with the shortest, lowest impedance path possible. Secondly, it modifies the way electric fields are formed around components. eg., if you take a resistor in free space and apply a voltage to it, electric lines of force are formed connecting its terminals together. This is not good as at high frequencies, the resistor is bypassed by a capacitance. Placing the resistor close to a ground plane causes the electric lines of force to connect to the ground plane instead of to the other terminal. In essence, it converts a capacitance across a resistor into two capacitances to the ground plane and the resistor is bypassed with a much smaller capacitance. This is why I suggested a ground plane on top of the circuit too and for ultimate rejection, having the resistors pass through the ground plane.Things are actually more complicated than this as there is also the magnetic field that becomes important at high frequencies but I think my mental model is good enough up to VHF.

author: RCinFLA
author_rank: Contributor
timestamp: February 15, 2020, 09:51:01 pm
content: Think about stray capacitance and inductance everywhere. Components and PCB layout.Primary stray for chip resistors is shunt capacitance. RF chip resistors are thin film on low dielectric substrate with single sided solder pads. Normal thick film ceramic (high-k substrate) chip resistors with full end cap terminations are good for a couple tenths of pF shunt capacitance. PCB solder pads for chip resistor are worth a couple of more tenth of pF. Ground plane to component solder pad are worth a couple more tenths of pF.PCB strays can hurt. Avoid ground plane behind chip solder pads.Metal film leaded resistor are disaster for series inductance. They are often trimmed to value with a barber pole spiral laser cut which makes a lossy inductor.

author: enut11
author_rank: Super Contributor
timestamp: February 17, 2020, 02:44:07 am
content: Quote from: duak on February 15, 2020, 08:39:30 pmHi @duakGood stuff on how ground planes work! Thanks for that.Could you please elaborate on "for ultimate rejection, having the resistors pass through the ground plane", with a diagram if possible?Hi @joeqsmith. About the 50ohm in-line load to the DSO, yes you are right. I discovered this also by accident but thanks for your reply.enut11

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 17, 2020, 03:05:30 am
content: For a verbal description -- consider two boxes sharing a common wall. There's one connector entering each box, and a hole through the common wall. The shunt resistors shall be placed by the hole, as close as possible on either side; the series resistor goes through.Or for a tee rather than pi arrangement, the shunt resistor is in the hole*, and the series resistors are placed close to it.*I've heard of PCBs actually being made this way, with a resistive layer that can be connected between pads and ground anywhere a termination resistor is needed. Like for ECL and LVDS circuits. You can have a resistor to ground, literally in the hole the connection is routed through.Note that the paths between connectors and hole must still be 50 ohm transmission line -- this is the key step missing from an earlier example:If the connections are simply routed down from the connectors, along the ground plane, then up to and through the hole, the lumpy response will straighten out.(Well, nearly -- this assumes the hole is plated-through, making a coaxial connection say. It looks like drilled copper clad, so there will be a gap between the two faces, not a direct connection. This can be solved by shortening the walls, so the connection can wrap over and around a contiguous ground, without interruptions.)Regarding paired resistors, probably better to have them closer together, but it depends on the transmission line impedance of that geometry. You could evaluate this, for example, using a field solver (full 3D preferably, but even a 2D prismatic solution like ATLC2 gives useful insight for much less time and money spent), using the approximate dimensions of the resistor bodies, spacing and ground plane. (Note that the resistor's conductive body is under the enamel; this might not have an obvious way to measure, so I hereby grant full permission to burn a resistor, utterly destroy, completely turn it to ash, and measure the film/foil/ceramic core dimensions.)Tim

author: enut11
author_rank: Super Contributor
timestamp: February 17, 2020, 03:26:11 am
content: Hi @T3sl4co1lI like your sense of humour.Heavy stuff indeed. I will have to read it several times to let it sink in

author: enut11
author_rank: Super Contributor
timestamp: February 17, 2020, 03:36:21 am
content: Quote from: RCinFLA on February 15, 2020, 09:51:01 pm@RCinFLAOK, I get that leaded resistors are history for VH frequencies and that metal film resistors may the the worst of the pick."PCB strays can hurt. Avoid ground plane behind chip solder pads" I think this means I cannot have a continuous ground plane under a solder pad. Seems to rule out using double sided PCB for VHF attenuators?enut11

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 17, 2020, 05:22:00 am
content: Quote from: enut11 on February 17, 2020, 03:36:21 amTo bring some subtlety to this -- the spiral cut isn't a problem, in and of itself. Consider the spiral itself: it can be analyzed as a helical waveguide. I don't pretend to know the inner workings of this myself, but the consequences are, it's a structure with impedance, velocity, all that -- just like any other transmission line. It's not an ordinary, well-behaved transmission line -- the impedance and velocity aren't constant with respect to frequency, it's dispersive. But we can still use a transmission line model over a modest range, or for that matter, reduce it to a low-frequency equivalent all the same!Of note, helical waveguides and resonators typically have quite high impedances. While typical TL geometries are 50-150 ohms, helices can be 100s, even a few kohms.So what does it mean for the transmission line to have resistance and impedance? If they're equal, it'll be very much a resistive element.Therefore: spiral-cut resistors, of values close to their transmission line impedance, have the widest bandwidth (largest resistive range, from DC to cutoff). Lower values are inductance-dominant, and higher values are capacitance-dominant. And the drop in bandwidth is approximately the same ratio as the ratio of resistance to Zo.Typical spiral-cut resistors have a sweet spot around maybe 50-300 ohms. That's partly driven by the size of the body over the ground plane, as well (assuming the PCB has one). Don't forget that the resistor's leads are usually welded to larger metal end caps, so an equivalent circuit (lowpass CLC) may be useful. (Fitting values to the equivalent is an exercise for the student..)So, relating back to attenuators -- you'll find the best results come using resistors in this range. If you need to use other values, you may find it's worthwhile staging it instead.As for SMT pads, beverycautious about cutting grounds. Consider: pads are just more metal on the signal path. It's a transmission line segment, likely very much shorter than the wavelength of interest, so manifests as a stray capacitance or inductance as the case may be. The chip's body does the same, too. If your Zo trace width is thinner than the component/pad width, that component will have a lower impedance, or manifest as capacitance; else, inductance. The further off they are, the less flat bandwidth you will have, etc.And the component forms a transmission line segment of known length. Is that enough to matter to your application? A few mm won't be sensible until GHz, don't worry about it. Or if you are up there, well,doworry about it -- and consider using 0402s or smaller, or perhaps an integrated module that can offer better characteristics than board-level components can.Removing ground under a trace or pad, increases the ground impedance, obviously; it acts as a series inductor. Bevery carefulabout putting anything near that opening, whether trace or component: it's a radiating source, a slot antenna (even if an electrically short one).Or if you're on multilayer board, you can pour ground on bottom and cut it out in the middle, to give a higher substrate thickness. Do use a via fence along this, to keep the planes from forming patch or slot antennas.Tim

author: duak
author_rank: Super Contributor
timestamp: February 17, 2020, 07:48:38 pm
content: enut11,I've attached an image of what I mean by passing the series resistors through the groundplane. I used some junkbox resistors and a piece of paper (instead of copper sheet). The theory here is that the electric field surrounding the series resistors has the greatest chance of terminating on the ground plane than on the opposite terminal.Ultimate Rejection is a term I borrowed from filters that describes the signal leaked around the filter outside of the passband. Since any real world attenuator has a passband where it meets its specs, it seemed a reasonable way to describe what's happening here.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 17, 2020, 08:11:36 pm
content: You may find that at 40MHz where you are interested in working at, that you may be able to get away with a lot.Let's start with a nice axial part. I have cut away the insulation to show you how these particular parts are constructed.Next, lets use some BNCs with no board and just wire the thing up. Some nice long leads.Now, lets toss it across the $50 Nano and sweep from a 1MHz to 40MHz.If you don't trust the Nano, here it is on my old HP3589A sweeping up to 150MHz.It's not quite an A/B compare as I am using different cables and I moved the unit and I'm sure I bent it a little. But I think you get the point. When I was a child I played with amateur radio for a while. All of my equipment was very old and if you looked inside, you would see a lot of construction you may think is suspect but at these low frequencies it's far less important. Of course, if you wanted to try and use this mess at 1.5GHz... It seems we have designed a 550MHz notch filter.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 17, 2020, 09:29:36 pm
content: Wouldn't surprise me if the notch varies with cable length, because of DM-CM conversion.Although, that's kind of silly if the cable isn't one or two feet long (depending on mode), isn't it.Tim

author: enut11
author_rank: Super Contributor
timestamp: February 17, 2020, 10:57:06 pm
content: Hi @T3sl4co1lYour words on component behaviour and PCB layout are most welcome even if my absorption rate is a little slow.Given a choice, for a 20dB VHF attenuator, what type of ground plane material would you choose?1) Single sided fiberglass/copper PCB?2) Double sided fiberglass/copper PCB?3) Solid copper sheet?4) Something else?Does ground plane metal thickness matter?enut11

author: enut11
author_rank: Super Contributor
timestamp: February 17, 2020, 11:06:32 pm
content: Quote from: duak on February 17, 2020, 07:48:38 pm@duak. Your illustration is perfect. I see that this type of construction would need to be planned and done in a certain order but will be worth itenut11

author: enut11
author_rank: Super Contributor
timestamp: February 17, 2020, 11:17:49 pm
content: @joeqsmithThanks. It is interesting to see what is under the paint on the metal film resistors. Are the miniature 1/8w carbon resistors trimmed in the same way?WRT the VNA shots, seeing is believing!I am still without proper cables, SMA connectors and adapters for my NanoVNA so cannot experiment any further here.Everyone's feedback is most welcome as it greatly accelerates learning. Answers to specific questions are timely - something you cannot necessarily get out of a textbook!enut11

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 17, 2020, 11:53:37 pm
content: Quote from: enut11 on February 17, 2020, 10:57:06 pmTo a first order, no, thickness and material don't matter much. Only height between signal and ground, and dielectric constant.I assume you mean for 1., a single sided board with THT components placed on top of it (either flying wherever, or secured on islands glued/soldered on top ala "Manhattan construction").Practically speaking, I prefer 2 sided copper clad, as it can be carved up to make traces and pads, and vias can be added (drill a hole, stuff wire in it, solder over both sides) to keep the ground pours in sync. I prototype SMT parts this way; here's a good example:https://www.seventransistorlabs.com/Images/GD9.jpgFor best results (i.e., including higher order effects), the foil should be thicker than several skin depths at the frequencies of interest, if possible; the dielectric should be low loss; the dielectric should be solid as well (compare stripline to microstrip: stripline uses one dielectric only, while microstrip has some field running through air, which propagates at a higher velocity, thus introducing dispersion); uhh, the foil surfaces should be smooth and free of corrosion (this is harder to do, as smooth/polished copper has poor bonding, especially with high-Q laminates like Teflon), etc.For example, this 20dB power attenuator I made -- which I think I only have a poor picture of here,https://www.seventransistorlabs.com/Images/DistAmp2.jpgoh, here's its backside,https://www.seventransistorlabs.com/Images/STF6N60M2_Amp.jpguses a TO-220 resistor for the brunt of it (the first shunt branch, I think it's pi type), and a few axial resistors for the series branch and to tweak the exact resistances. I think it's 75R 20W in parallel, 330R 1W (carbon film) in series, 75R 1/2W in parallel, plus whatever corrections.Heh, also the 330 ohm resistor(s) have taken a bit of brown color, as they aren't quite properly rated for operation at 20W it seems. Design mistake.Anyways -- as far as I can tell, this is flat out beyond 300MHz (give or take a dB), based on my measurements with a bad noise generator and HP 8590A spec (I don't have a TG, unfortunately). The layout is crude, more or less over ground plane, and seems fine for VHF work.With respect to the above mentioned impedance theory, it's convenient that the TO-220 device has a very average resistance, and the axial resistors are somewhat higher values as fits their spiral-cut design.Lead lengths and stray capacitances will take over at higher frequencies, sooner or later and give or take how flat you need it to be. The component leads are all relatively thin, and some distance above ground, so will have higher TL impedances, 100-150 ohms say. The TO-220 tab to heatsink acts as a wide pad, low-Z trace or capacitance, and the resistor end caps act similarly. Overall, the various components will have a CLC lowpass filter response, probably somewhere a bit below 1GHz, plus zeroes as the resonances couple into each other.Response probably looks much like joeqsmith's lashup, just with all the crud shifted to a bit higher frequencies due to the improved grounding, and perhaps not as exaggerated in magnitude because the RLC equivalents aren't so far out of whack.Tim

author: joeqsmith
author_rank: Super Contributor
timestamp: February 18, 2020, 02:13:59 am
content: Staying with the same components previously shown I trimmed them and added a metal plate. Similar construction to OP's first approach.These are the same cables and adapters previously used but notice we no longer have our 550MHz notch and the overall flatness is greatly improved. According to our cheap VNA, even at 300MHz, we are within a half dB.As a reference, I have included a Coline PN# 120085 20dB attenuator. This part is rated DC to 1GHz with a +/-0.2dB tolerance. The Nano of course paints a completely different story, but again, it's $50. Don't expect much from it above 300MHz. What you can see is that up to 400MHz, the Coline part is basically flat and we can safely say that the half dB we measured with the home made part is real.

author: enut11
author_rank: Super Contributor
timestamp: February 18, 2020, 08:05:36 pm
content: Hi @joeqsmithExcellent way to demonstrate the difference between components floating in space vs a ground-plane construction with trimmed leads for VHF applications.Supplies from China seem to be taking longer to arrive - may be due to the current health crisis?

author: enut11
author_rank: Super Contributor
timestamp: February 18, 2020, 08:27:22 pm
content: @T3sl4co1l"For example, this 20dB power attenuator I made -- which I think I only have a poor picture of here,https://www.seventransistorlabs.com/Images/DistAmp2.jpg"Thanks for showing and explaining your VHF construction methods. Now, what is that very complicated setup supposed to do?enut11

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 18, 2020, 11:03:19 pm
content: Huh, odd, thought I made a post about it, doesn't seem to exist anymore? Anyway, it's testing a 20W, 30MHz distributed amplifier, with a switching supply (because why not?) powered from a LISN for extra filtering, a white noise generator, preamp, and more amp, depending on which configuration I was testing. Pictured was one preamp and an attenuator, so, checking small-signal response, return loss, etc. The 4W 50MHz amp I made specifically to test this thing at full power, actually. Since it has, what was it, 17dB gain I think, so it needs a good few watts to get going.Oh, heh, so the 6dB attenuator is built on copper clad, using 0805 chips. On topic content.Tim

author: joeqsmith
author_rank: Super Contributor
timestamp: February 19, 2020, 02:11:41 am
content: Quote from: enut11 on February 18, 2020, 08:05:36 pmI suspect so. A little over a week ago, I ordered a few things from China including those low cost attenuators. One order has yet to ship. One shows mid next month, the other the following month.

author: enut11
author_rank: Super Contributor
timestamp: February 19, 2020, 07:59:12 pm
content: What's wrong with my NanoVNA. This is what I see with nothing connected.Also, cannot calibrate it?? Is there a way to reset it to factory defaults?enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: February 20, 2020, 02:26:42 am
content: I understand that there is now a manual for the nano. It may be time for you to join the group, if just to gain access to their secrete repository.You may be interested in the following:https://www.edn.com/pcb-fixtures-improve-component-measurements/He sells these boards along with a few others that may be helpful.https://www.sv1afn.com/en/other/

author: joeqsmith
author_rank: Super Contributor
timestamp: February 27, 2020, 06:56:45 pm
content: The plating is a bit off and note a resistor kicked up and solder to the backside.

author: ogden
author_rank: Super Contributor
timestamp: February 27, 2020, 07:59:03 pm
content: Quote from: joeqsmith on February 27, 2020, 06:56:45 pmThose on the back are spare resistors

author: enut11
author_rank: Super Contributor
timestamp: February 27, 2020, 08:48:24 pm
content: Hi @joeqsmithMy attenuator set never arrived and they gave me my money back. May be a bit of a crisis over in China.I was going to compare the commercial unit to my own home built attenuators.It will be interesting to see your VNA test results.enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: February 28, 2020, 01:51:35 am
content: Again, from their ad:Direct: 0dB (reference)Level 1: 10 0.8 dBLevel 2: 20 1.1 dBLevel 3: 30 1.5dBStanding wave ratio: 1.20I fired up the old HP8754A. The screen is calibrated 1:1. Keep in mind that I use home made standards to cal it. My calibration routines assume the standards are perfect. At some point I will have a better VNA and we can remeasure them.I don't have any plans to try and measure them with the nano because of the higher frequencies.20dB_1p3GHz: 20dB attenuator swept to 1.3GHz30dB_1p3GHz: 30dB attenuator swept to 1.3GHz20dB_intstep_2p6GHz: This is the HP8748A's internal step attenuator set to 20dB, with the doubler, sweeping to 2.6GHz30dB_intstep_2p6GHz: This is the HP8748A's internal step attenuator set to 30dB, with the doubler, sweeping to 2.6GHz20dB_2p6GHz: 20dB attenuator swept to 2.6GHz30dB_2p6GHz: 30dB attenuator swept to 2.6GHzMWM_18GHzTerm_SWR_2p6GHz: This is a Midwest Microwave 18GHz 50ohm terminator. We are looking at the SWR. At 160MHz, 1.07:1 and 2.2GHz, 1.2:1.The MWM terminator was then attached to the attenuators while measuring their SWR.20dB_SWR_2p6GHz: SWR 160MHz 1.03:1, 2.12GHz 1.14:130dB_SWR_2p6GHz: SWR 160MHz 1.05:1, 2.2GHz 1.18:1I then connected the three attenuators in series. The HP8501A was set to average eight sweeps. 40dB of offset was added on the thumb wheel switches so the top of the graph is now 0dB.

author: ogden
author_rank: Super Contributor
timestamp: February 28, 2020, 05:41:29 pm
content: Can't you show 1dB/div instead of 10dB/div vertical scale? Your NanoVNA software is able to show 0.3dB/div orsomething like that.

author: enut11
author_rank: Super Contributor
timestamp: February 28, 2020, 07:36:58 pm
content: @joeqsmithLooks OK to me. Some brief comments on what you see on the charts and your opinion on how good the attenuator set is would be appreciated.enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: February 29, 2020, 01:05:34 am
content: Quote from: enut11 on February 28, 2020, 07:36:58 pmIf I set the VNA to 1dB/division, the software is also then 1dB/div. Then use the VNAs internal step attenuator with a thru to calibrate to. For each attenuator the center line represents the nominal value. So, the center line is 20dB for the 20dB attenuator and 30dB for the 30dB attenuator. In all cases we are sweeping to 2.6GHz.20dB_2p6GHz_1dBdiv & 30dB_2p6GHz_1dBdiv are the low cost attnuators. For a comparison, I have included a 30dB Midwest Microwave 18GHz part. There is a substantial difference between the cost of these parts.While the HP8754A can read down to 0.25dB/division, notice that even after calibrating the unit to the 30dB internal attenuator that the system has a fair amount of noise. Like the $50 Nano, this old system certainly has it's limitations.This first set of low cost attenuators performs pretty much how I would expect at these lower frequencies. Once I am setup, we can see how they perform at higher frequencies. The noise on the newer boat anchor is much improved over the 1970s system as well.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 29, 2020, 02:05:04 am
content: Scam or real? $2600 USD, seems way too good to be true!!https://www.ebay.com/itm/Agilent-E8358A-PNA-Network-Analyzer-300-kHz-to-9-GHz-Opt-010/352986648287?hash=item522fa4cedf:i:352986648287

author: hendorog
author_rank: Super Contributor
timestamp: February 29, 2020, 03:11:42 am
content: Not sure any conclusion can be drawn from the higher res traces.Without the cal kit characterised I mean.

author: enut11
author_rank: Super Contributor
timestamp: February 29, 2020, 04:41:11 am
content: Quote from: joeqsmith on February 29, 2020, 02:05:04 amI just checked my piggy bank and I am a little short on funds...

author: ogden
author_rank: Super Contributor
timestamp: February 29, 2020, 07:52:16 am
content: Quote from: hendorog on February 29, 2020, 03:11:42 amWithout characterised cal kit you shall avoid any other conclusion except one: calkit is not characterisedWhen we assume that calibration is ok, now at 1dB/div we have better chances to estimate accuracy of attenuators which BTW is surprisingly good considering price.

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 29, 2020, 10:32:47 am
content: Quote from: joeqsmith on February 29, 2020, 02:05:04 amTotally legit:https://www.ebay.com.8641224.com/CT/c1875.html(*)(*) Yes, sarcasm (for people that don't see it)

author: joeqsmith
author_rank: Super Contributor
timestamp: February 29, 2020, 04:53:44 pm
content: Quote from: hendorog on February 29, 2020, 03:11:42 amOdd. The higher res traces are S21 only and I am using a good thru with the HP's internal attenuator to calibrate the system. This is a 4GHz HP branded attenuator. Consider that with the Midwest Microwave part installed, it is within +/-0.5dB. Now, when we install the low cost attenuator, we can clearly see it's not near as flat and has a bit of an offset. I have far more confidence with the Midwest Microwave matching with the HP part when using a good thru, than I do with the low cost attenuator. You may see it otherwise.Quote from: PA0PBZ on February 29, 2020, 10:32:47 amGone! That was the deal of the year right there.

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 29, 2020, 06:39:25 pm
content: Quote from: joeqsmith on February 29, 2020, 04:53:44 pmWell, the second link is still active, so you can still pay if you want

author: joeqsmith
author_rank: Super Contributor
timestamp: February 29, 2020, 06:49:20 pm
content: Quote from: PA0PBZ on February 29, 2020, 06:39:25 pmClick on your area. When I did this, I get a 404 Not Found error where it would come up before. I assume this means it was sold.

author: enut11
author_rank: Super Contributor
timestamp: February 29, 2020, 07:27:35 pm
content: Quote from: enut11 on February 19, 2020, 07:59:12 pmI was trying to calibrate my NanoVNA and the OPEN test (far right marker) would not work.There is a lot of conflicting advice out there on how to calibrate this device, whether to reset or not, whether to save or not, etc.I came across this website and all is good now. Change the language top left and scroll down several pages for the Cal notes.enut11http://ha3hz.hu/hu/home/top-nav/12-seged-berendezesek/15-nanovna

author: joeqsmith
author_rank: Super Contributor
timestamp: February 29, 2020, 07:37:23 pm
content: Were you able to get it working or are you still having problems with it?I was using the Reset prior to running the calibration. The save is optional. Save 0 would be loaded on power up. The other have to be manually loaded.

author: enut11
author_rank: Super Contributor
timestamp: February 29, 2020, 07:45:42 pm
content: Yes, my Nano is now working.What I am doing is learning how to use it and what it is telling me...

author: joeqsmith
author_rank: Super Contributor
timestamp: March 01, 2020, 01:32:50 am
content: Quote from: enut11 on February 29, 2020, 07:45:42 pmGood to hear. You may find that making a simple test jig like that one I linked earlier with the solder braid, may be helpful. Something so you can easily try different components and such.This is the cal kit I am working on for the higher frequencies. I also now have an SMA along with a few sections of shorted coax and the Ts.https://www.eevblog.com/forum/rf-microwave/get-ideal-networks-from-cal-kit-parameters/msg2921098/#msg2921098

author: joeqsmith
author_rank: Super Contributor
timestamp: March 01, 2020, 07:34:10 pm
content: It took FireFox a while to catch up.Shown are the new standards along with some of the test boards I made for the Nano resting on the new boat anchor. These new standards were characterized using a set of real standards.Like that really bad home made attenuator I show, at these lower frequencies we can get away with a lot of errors and still get reasonable results. Well, at least for my hobby experiments.... Using the Nano's standards which I have no data for at all, running a section of coax to 900MHz, we can see the peak to peak ripple is about 0.4dB, which gives us a source match of 33dB. Running the T-check over the same frequency span, we can see its around 10% error at 800MHz.Even without having any data for these, they are not the limiting factor when used with the Nano. Running these same tests on the Nano would look like total garbage as the noise is really poor above 400MHz. Keep it below that and you should get some pretty decent results.I have looked at a few filters in the GHz range using Radiolistener's firmware which supported 1.5GHz. Even at these frequencies, the Nano has enough dynamic range to get a feel for what things are doing.https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg2703812/#msg2703812

author: joeqsmith
author_rank: Super Contributor
timestamp: March 03, 2020, 05:43:14 pm
content: The second set of attenuators has yet to arrive but at least they claim to have shipped. Looks like mid month.I have been getting some help from Mario with my calibration questions.https://www.eevblog.com/forum/rf-microwave/get-ideal-networks-from-cal-kit-parameters/So far, getting a system to produce any sort of meaningful results, to measure these low cost attenuators, has been a bust. There are a lot of variables to juggle with this new boat anchor. Hope to have things sorted out by the time the second parts arrive.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 05, 2020, 03:38:00 am
content: Attached is the T-check for the uncompensated 3.5mm home made standards up to 2GHz.I also had a look at the low cost attenuators at 4GHz and am confident they do not come near meeting that 1.5dB flatness at 30dB. It doesn't appear to be even close when compared with a commercial part.While I have made some progress, the new standards are not good enough to have any sort of confidence in the SWR at these frequencies.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 06, 2020, 01:54:56 am
content: MWM vs the low cost attenuator swept to 4GHz. Also shown is the home made 4-stage 50dB attenuator that I had trimmed. Fairly flat to around 2GHz, then it takes off. Last plot shows a commercial 50dB attenuator.I'm actually impressed the homemade 50dB attenuator is this good.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 06, 2020, 11:16:09 pm
content: The second type of low cost attenuators arrived. And while they do not have the protective caps, the design looks more what I would expect for something spec'ed at 4GHz.Plating finish at least looks more uniform.I still have no way to measure the SWR but I will go ahead and sweep the S21 and see how it compares.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 07, 2020, 12:34:48 am
content: Yellow is the MWM commercial part, purple is the green PCB, red is the blue PCB. It looks like it may actually meet the stated specs for flatness. Pretty impressive for the price.Once I get the old boat anchor fully up and running, I will retest them.

author: David Hess
author_rank: Super Contributor
timestamp: March 07, 2020, 01:37:11 am
content: Would performance be better with a more symmetric layout that doubles the number of shunt resistors?

author: joeqsmith
author_rank: Super Contributor
timestamp: March 07, 2020, 02:11:55 am
content: To be honest, it's way outside of my area. Most of my hobby experience is below 2GHz. It would be hard for me to say where to begin. Maybe use something better than FR4 to start and some better connectors. When I first saw the previous attenuator design, I was concerned to see the single plane with those vias. All that added inductance can't be good. It wasn't.These are fairly inexpensive if you don't mind the wait. Maybe someone will verify my findings for starts.I bought two of each type and planned to see if I could improve them. The first one, I doubt I will do anything with it but maybe I will try some different configurations with these new ones.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 07, 2020, 08:44:21 pm
content: I swapped out all the parts for 2X0603s and trimmed off some of the excess around the launch connectors. In the end, I absolutely destroyed the flatness.The width of the 2X0603s could be the problem. I may put the original ones back on the board and see how that behaves.I have gained an appreciation for our friends in China who made this little board work so well at such a low cost.

author: enut11
author_rank: Super Contributor
timestamp: March 08, 2020, 07:05:28 am
content: Thanks @joeqsmith. I just bought the green 0/10/20/30dB set (again) now that I know it has good performance for my frequency range (currently <1GHz) and will use them to compare the performance of my home made attenuators.Staying with those 'horrible' metal film resistors because I have some, I built two new 50 ohm 20dB attenuators with SMA connectors and had a friend check them with the following results:All I can conclude at this stage is that the H-pad is better than the T-pad, but I don't know why. The resistor junctions are floating very close to the ground plane.enut11

author: ogden
author_rank: Super Contributor
timestamp: March 08, 2020, 07:32:51 am
content: AFAIK real world Pi attenuators (shunt first) have better return loss compared to T. If possible - ask your friend to measure not only S21 but S11, S22 as well. BTW "green 0/10/20/30dB set" also uses Pi, not T type. Could be nice to see measurements of your first attenuator shown in the first post.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 08, 2020, 05:36:49 pm
content: It appears now that you have seen some higher frequency data off your friends system, the hook has been set.Both of those look pretty good at 250MHz. Your friend may be able to help you out with your experiments and learning how to use your Nano.

author: enut11
author_rank: Super Contributor
timestamp: March 09, 2020, 07:30:46 am
content: Yes, he has some nice equipment but lives 250Km away.I came across this VNA demo board on eBay. I hasSMAscrewSMB connectors and demonstrates the proper response of various component s. A bit expensive but it gives me some ideas.

author: enut11
author_rank: Super Contributor
timestamp: March 09, 2020, 09:06:04 am
content: First tests with my NanoVNA, these span 1-300MHz which is the basic range for the Nano.Comparing:1) the original boat-anchor attenuator with BNC connectors from the start of this thread (BA1).2) slightly improved boat-anchor attenuator with BNC connectors (BA2)3) improved Pi attenuator with SMA connectors4) improved T attenuator with SMA connectors5) commercial 6GHz in-line attenuator for reference (6G)

author: enut11
author_rank: Super Contributor
timestamp: March 09, 2020, 09:32:03 am
content: Attaching 'BA1' 1-300MHzMy conclusions so far:1) all attenuators are OK from 1-300MHz (blue line) with small dB differences due to resistor tolerances2) The yellow line (CH0 LOGMAG reflected signal?) shows significant improvement with each successive build.Using the commercial 6GHz as reference, it appears that the yellow line should be as low as possible across the frequency sweep.BA1, my first BNC 20dB attenuator is the worst as frequency goes up, even with all that shielding!BA2, also BNC equipped, is a little better but still poor.SMA equipped T atten and Pi atten are better but no match for the commercial unit (6G)For me it is good to see some progress in performance due to improved layout and connectors.More to come...enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: March 09, 2020, 12:48:25 pm
content: Quote from: enut11 on March 09, 2020, 07:30:46 amIn the picture, it looks like SMBs. SMA would be much better for this.QuoteTry leaving the CH0 cable open on one end, then try adding the 50 ohm terminator. Then try the short. You will find all of signal is reflected back with the short and open, giving a reading near 0. With the 50 ohm terminator, nothing will be returned and the reading will be -infinity. Well, obviously it's not a perfect world but you will get the point.For the really low cost attenuators, they publish the SWR which is giving you some figure of merit for the match. I think the Nano can read that directly. For a perfect match (like the 50 ohm terminator) it will read 1.0. Try it with the open and short as well. The low cost attenuators were advertised with an SWR of 1.2. They don't show a different SWR for each attenuator.I have been avoiding showing you the match (reflection) to avoid adding confusion. Up to 2GHz, I can provide some reasonable numbers but moving beyond that requires a higher grade cal kit than I currently have. Hopefully I will have that sorted out soon. When I made the video for the Nano, I measured some resistors to check the SWR. You will find that section here:https://youtu.be/mKi6s3WvBAM?t=2167You can try these same experiments to help cement some of these concepts.Too bad your friend is so far away. They could have been a very good resource.

author: enut11
author_rank: Super Contributor
timestamp: March 09, 2020, 07:43:58 pm
content: " 2) The yellow line (CH0 LOGMAG reflected signal?) shows significant improvement with each successive build.Using the commercial 6GHz as reference, it appears that the yellow line should be as low as possible across the frequency sweep.Quote from @joeqsmithTry leaving the CH0 cable open on one end, then try adding the 50 ohm terminator. Then try the short. You will find all of signal is reflected back with the short and open, giving a reading near 0. With the 50 ohm terminator, nothing will be returned and the reading will be -infinity. Well, obviously it's not a perfect world but you will get the point."Pix of CH0 Open, CH0 50ohm and CH0 Short.Is the display for CH0 50ohm OK?

author: enut11
author_rank: Super Contributor
timestamp: March 09, 2020, 10:31:35 pm
content: Second tests with my NanoVNA, these span 1-900MHz which is the extended range for the Nano.I believe beyond 300MHz the Nano relies on harmonics with reduced performance.Comparing:1) the original boat-anchor attenuator with BNC connectors from the start of this thread (BA1).2) slightly improved boat-anchor attenuator with BNC connectors (BA2)3) SMA improved Pi attenuator4) SMA improved T attenuator5) commercial 6GHz in-line attenuator for reference (6G)Again, up to 250MHz, the 6GHz commercial attenuator shows good performance. Beyond that, performance deteriorates and this may be a limitation of the Nano.For my home made attenuators, ranking is as before.There is room for improvement however...

author: enut11
author_rank: Super Contributor
timestamp: March 09, 2020, 10:39:30 pm
content: Looking at BA1, the gain (loss) blue line goes crazy at the top end.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 09, 2020, 11:50:36 pm
content: Quote from: enut11 on March 09, 2020, 10:39:30 pmOf course it does. It's $50, not $50,000.Your SOL data looks what I would expect. For a reference, RCLoad was taken from my Nano.(added)Changing to display, trace, trace0, format, SWRShowing SWR of the 50 ohm load and a 100 ohm load.Measuring the SWR of one of the home made 20dB attenuators.(should add that you would want to terminate the unused port)QuoteGo back and look at some of the data I have provided comparing the Nano with my other VNAs. Keep it below 400MHz or so. I would trust a high grade attenuator long before I would trust the $50 Nano once you get above 300MHz.

author: enut11
author_rank: Super Contributor
timestamp: March 10, 2020, 04:19:50 am
content: Correct, the Nano seems to work well up to ~300MHz.For my four home made 20dB attenuators from above, the SWR at 300MHz is:1) BNC BA1 - 2.00 (ie very poor)2) BNC BA2 - 1.443) SMA Pi - 1.13 (not too bad?)4) SMA T - 1.16 (ditto?)5) Commercial 6GHz - 1.05 (very good)enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: March 10, 2020, 12:11:14 pm
content: After you receive your low cost attenuators, it would be interesting to have your friend characterize them with their system.Quote from: enut11 on March 10, 2020, 04:19:50 amThe following article is on SWR. It may help you interpret your results.http://www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf

author: joeqsmith
author_rank: Super Contributor
timestamp: March 10, 2020, 11:59:51 pm
content: Graphs showing the reflection coefficient using the Nano, sweeping from 1 to 100MHz, using a from 0 to 30dB step attenuator with 1dB/step. You can see it's fairly linear to 16dB or so. 20dB even at a MHz looks like it is asking a bit much for your $50.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 11, 2020, 12:28:53 am
content: If I step from 0-20dB but sweep from 1-300MHz which is in the region you are operating, you can clearly see how nonlinear the Nano is. Ideally you would want to constrain all of your measurements to avoid these errors.You may find you get to a point where you want something better than the Nano. My advice is first, learn as much as you can with the Nano. Then if you still decide to upgrade, consider even my old HP8754A will put the Nano to shame when we start looking at noise, flatness of the signal path and linearity.Maybe by then the Nano V2 will be readily available and we will have a better idea on if it would be a suitable upgrade.

author: ogden
author_rank: Super Contributor
timestamp: March 11, 2020, 05:46:41 pm
content: Quote from: joeqsmith on March 11, 2020, 12:28:53 amWhy don't you demonstrate it by running linearity test of 0 to 30dB step attenuator?

author: enut11
author_rank: Super Contributor
timestamp: March 12, 2020, 07:08:56 am
content: Quote from: joeqsmith on March 10, 2020, 11:59:51 pmThanks @joeqsmith. A very interesting way to present data and show the limitations of the NanoI have just acquired some SMD resistors and looking to build a very small 20dB attenuator.Considering this method which includes a small double sided PCB for ground and soldering the resistors between and across the SMA pins.Shown next to my boat-anchor attenuator to lend scale. Metal film resistors will not be used in this attenuator.Hardest part will be how to hold the SMD resistors in place while soldering.enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: March 12, 2020, 11:34:32 am
content: As you continue to improve your construction practices, just keep in mind my early posts where I've shown some of the problems with the Nano. If you find your new design is not as flat as you may expect, you may want to make the drive to your friends place or ship the parts to them to. With the one you are now making, depending on the frequency range, I expect you will see a pretty big difference between the two VNAs.https://www.eevblog.com/forum/projects/20db-rf-attenuator-seeking-feedback-to-improve/msg2902996/#msg2902996

author: enut11
author_rank: Super Contributor
timestamp: March 13, 2020, 03:56:56 am
content: Well working with tiny SMD resistors is a challenge for me. The ones I have are only 2mm long.Already lost 2 just by picking them up with tweezers! Popped out never to be seen again.I did manage to measure resistance with a home-made clip. This one was stamped 5110 meaning 511 ohms.enut11

author: ogden
author_rank: Super Contributor
timestamp: March 13, 2020, 05:23:57 am
content: Quote from: enut11 on March 13, 2020, 03:56:56 amThose are 0805, considered "big" from modern (automatic) SMT point of view. Note that your SMA end launch (edge) connectors have little over 2mm distance between bottom of the central pin and bottom of the bottom legs. Hint: you can use same "dead bug" technique as for your boat anchor attenuator by putting whole SMA edge-launch connectors on top of solid ground plane. Start with single connector, then solder resistors, when done with resistors - only then add 2nd SMA at the end of resistor chain.

author: enut11
author_rank: Super Contributor
timestamp: March 13, 2020, 09:20:16 am
content: Hi @ogden. I had already soldered the SMD resistors to the SMA connectors before I read your post. I hope I got it right. I tested it at DC but have yet to test it at VHF.enut11

author: ogden
author_rank: Super Contributor
timestamp: March 13, 2020, 03:22:27 pm
content: No, you did not place connectors as I told - when no parts of connector touch bottom side of PCB. Is it so that you use double sided PCB with top copper layer still in place, very, very close to central pins? - Not good.

author: enut11
author_rank: Super Contributor
timestamp: March 13, 2020, 07:50:34 pm
content: @ogden, thanks. Now I understand. I will also make your idea and it will be interesting to compare them.enut11

author: rf-messkopf
author_rank: Regular Contributor
timestamp: March 14, 2020, 01:02:20 am
content: Interesting thread, which shows that it is not at all easy to make good attenuators at the board level from standard chip resistors. I became curious and ran a quick impedance measurement on four standard 0805 resistors (27 Ohms, 100 Ohms, 510 Ohms, 1000 Ohms) up to 1.8 GHz.The lower resistor values tend to increase with frequency, whereas the higher ones tend to drop. The sweet spot seems to be somewhere around 100 Ohms. It becomes a complex optimization problem to manufacture a flat attenuator from these.For the measurement the resistors were soldered to a PCB test jig. The calibration planes of the measurement lie exactly at the outer edges of the SMD pads. The analyzer was calibrated by TRL with TRM extension at low frequencies. Since the impedance standard in this calibration is the wave impedance of a trace on the test jig (a grounded and fenced coplanar waveguide, manufactured in a cheap and non-impedance controlled pool process), the absolute values of the resistances indicated in the analyzer printout may be off by a few Ohms (the 100 Ohms resistor measures almost exactly 100 Ohms at DC, so that's roughly 5% high at low frequencies). In fact, I measured the coplanar waveguide impedance a few Ohms below 50 Ohms, so the values should read a little high. But the general trend is clearly visible anyway.See here for a picture of the test jig:https://www.mariohellmich.de/projects/trl-cal/img/trl-fixture.jpg

author: ogden
author_rank: Super Contributor
timestamp: March 14, 2020, 02:23:40 am
content: Quote from: rf-messkopf on March 14, 2020, 01:02:20 amYourTRL Calibrationandcheap SMA cal kit characterizationprojects are even more interesting read. Well done!QuoteWe can conclude that best "DIY 50-Ohm load standard" could be made out of 2x100 Ohms, not 1x50. Thanx for valuable input.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 14, 2020, 03:48:51 pm
content: Welcome to the discussion Mario and again, thank you for all the help you've provided.I wonder how other package sizes would behave and also what happens at higher frequencies. After making those changes to that low cost attenuator, the world above 2GHz seems to come with a whole new set of problems.Thinking about your test board, assuming that this was used as the standard and that the reference seems to be made from 2X100 ohm 0805s, is this biasing the the results?

author: joeqsmith
author_rank: Super Contributor
timestamp: March 14, 2020, 09:58:33 pm
content: Looking at 0603s with the Nano sweeping from 50K to 1.5GHz. Values are 24.9, 100, 499 and 1K ohms. There does appear to be an upward trend with the lower value and opposite with the higher values.

author: rf-messkopf
author_rank: Regular Contributor
timestamp: March 14, 2020, 10:01:23 pm
content: Quote from: joeqsmith on March 14, 2020, 03:48:51 pmYou are very welcome, Joe.Quote from: ogden on March 14, 2020, 02:23:40 amThank you, that's appreciated.Unless the resistors are dedicated RF resistors, two 100 Ohms in parallel should indeed be more flat.Quote from: joeqsmith on March 14, 2020, 03:48:51 pmThe board only works up to about 1.8 GHz because then the phase shift of the line approaches 180 degrees and the TRL calibration breaks down. For higher frequencies I would have to make a new test board with another shorter line and then use multiline TRL for calibration.Concerning your second question: The primary impedance standard on the test board is the wave impedance of the line, not the two 100 Ohms resistors in parallel. They have not even been used for calibration. I did measure a match standard in addition to the TRL calibration standards, but that is not really necessary when measuring from 50 MHz onward. It would only serves to extend the calibration to lower frequencies where the phase shift of the line approaches 0 degrees. It should have almost no influence on the displayed results. Moreover, in an independent test I have measured the wave impedance of the line and found it to be about 6% below the nominal 50 Ohms. That matches the measurement result of the 100 Ohms resistor, which reads about 5% high.I hooked the board to the analyzer again with the 100 Ohms 0805 resistor in place. The attached plot now also shows the real and imaginary components of the impedance. The resistor becomes slightly inductive at higher frequencies.I also soldered a 100 Ohms 0603 resistor to the 0805 footprint of the test board. There is virtually no difference to the 0805.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 14, 2020, 10:27:08 pm
content: Sorry, I completely missed the TRL cal. With the 100 ohm being the most stable of the four, I wouldn't expect to see as dramatic effect using the 0603 compared with the 1K. With the Nano, it may be difficult to see any sort of trend.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 14, 2020, 10:55:39 pm
content: Using the Nano to log 20 sweeps from 50KHz to 1.5GHz using the 1K ohm 0603 compared with a 1K 1206 package. At least with the Nano, there appears to be little difference. Your lab grade VNA may show otherwise.

author: rf-messkopf
author_rank: Regular Contributor
timestamp: March 15, 2020, 12:06:55 am
content: Quote from: joeqsmith on March 14, 2020, 10:27:08 pmYes, one would have to run more extensive tests with several values for each size. But that becomes tedious since the resistor needs to be soldered down each time, though that is the most faithful way of measuring.Another question is how such measurements could be used for attenuator design. Since the TRL cal using the test board puts the reference plane right at the edges of the SMD pads, one could import the measured S-matrices into a simulation program, add traces (e.g. microstrip) and vias, and calculate or optimize the overall response. Again a tedious task. And it will never become as good as a high performance coaxial attenuator:https://www.mariohellmich.de/projects/sma-cal-kit/img/20db-att-meas.png.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 15, 2020, 01:34:37 am
content: Quote from: rf-messkopf on March 15, 2020, 12:06:55 amWhat's the Mfg and PN of the attenuator in your plot? That's a very nice bit of hardware!!To answer your question, there could be a few reasons to roll your own. The requirements may warrant the cost or be such that its easily achieved. Perhaps it needs to be integrated as part of a larger design and on the same PCB. In the case of this thread, I assumed OP was wanting to learn more about it, which is certainly a valid reason as well.Just for some sort of sanity check, the attached plot is using the same setup used to cal the Nano. This is not the newer standards I am attempting to put together. I'm still waiting on my friend to send over those parts they characterized. We can now see some difference between the two resistor packages. I would imagine if I ran it higher the difference would become more apparent.

author: enut11
author_rank: Super Contributor
timestamp: March 15, 2020, 07:25:44 am
content: Quote from: ogden on March 13, 2020, 03:22:27 pm@ogdenSince I have only 2 SMA connectors left, I want to get it right. I will be using 0805 type SMD resistors.I am building the 20dB 50 ohm Pi attenuator using four 120 ohm to ground and two parallel 510 ohm in series with the SMA center pins.Now, the center pin to ground plane distance is ~3mm, ie too far for the 2mm 0805 devices.The distance of the center pin to (grounded) side pins is ~2mm.I seems the only way I can build this attenuator is off the ground plane. Is this what you intended?enut11

author: ogden
author_rank: Super Contributor
timestamp: March 15, 2020, 08:10:17 am
content: I am afraid that connector do not lay flat, central pin is tilted away from PCB. My "cheap" SMA edge mount connector for 1.6mm PCB measure 2.5mm which is "good enough" to put 0805 in-between. You may want to desolder this connector, then clamp or tie it down to new PCB in proper position. Double check that it stands properly & still, ONLY THEN solder. BTW you got 1.6mm or 1.8mm PCB connector? Latter could be "too big" indeed.Other option for you would be to copy "low cost attenuator" PCB by etching/cutting/dremelling it.How did your attenuator shown inthis postmeasure with NanoVNA?

author: rf-messkopf
author_rank: Regular Contributor
timestamp: March 15, 2020, 08:37:43 pm
content: Quote from: joeqsmith on March 15, 2020, 01:34:37 amThat is a HP part no. 85053-60001 attenuator with 3.5mm air dielectric connectors, rated to 26.5 GHz, see the attached picture (not easy to take a photograph due to the glare). It it part of the HP 85053A verification kit. I don't know exactly but I think it will set you back by a four digit amount when you buy it separately.It would surely be possible to get an even more flat response by a better test setup. It was connected by Sucoflex 104A cables with precision SMA, which are good but not intended for precision VNA measurements, and are not designed to be phase stable. At 0.01 dB/division cable flexure has a significant influence on flatness, and connector torque becomes a real concern (and at 0.001 dB/div you can sometimes see the effect of thermal expansion when you touch your hardware). The mating of 3.5mm connectors with precision SMA is also a compromise.Should I become bored during the shutdown I will get the 3.5mm test port cables out and see if I can get a better result.Quote from: joeqsmith on March 15, 2020, 01:34:37 amI wonder at which point you would run into repeatability issues with different resistors when you design with measured S-matrix data, and different PCB batches. FR4 is not the most stable material when it comes to RF, and you may want to use a Rogers material. But it is certainly true that there are applications where attenuators from standard components make sense.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 15, 2020, 09:37:14 pm
content: Thanks. I figured it had to be some sort of metrology grade component.I came across this YT channel and started watching a few of his videos. This one talks about a study that was done using several 1206 resistors. It may be of some interest.https://youtu.be/D5mIJzKAMSI?t=664His most recent video adds a bit more.Getting things somewhat true when soldering or using glue, I will normally block up the parts. The M/F was made by soldering all four prongs, then inserting a bit of teflon where they PCB would normally be. A shield was then soldered to the lower half. It could be covered with copper foil tape to seal it.

author: enut11
author_rank: Super Contributor
timestamp: March 16, 2020, 09:21:05 am
content: Quote from: ogden on March 15, 2020, 08:10:17 amThankfully my latest attenuator (from post #147) seems to measure up well against the silver 6GHz commercial 20dB attenuator (post #131 and #135)NanoVNA plots look very similar in the 300MHz and 900MHz sweeps. Again, beyond 300MHz, the Nano seems to be out of its depth.Currently working on an improved SMD version suggested by @ogden. Waiting for more SMD resistors to arrive.enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: March 17, 2020, 12:42:49 pm
content: I've been thinking about your TRL fixture but am VERY ignorant about it and have been doing a little reading. The following link has a spreadsheet to calculate the lengths and number of them:https://www.microwaves101.com/encyclopedias/trl-calibrationThey also offer some practical guidelines, like using precision connectors. Most articles talk about the TRL obtains the most accurate results at the higher frequencies. I find it odd they offer standard SOLT kits rated for 10+GHz.I've been working on setting up to be able to run experiments in the 2GHz+ which is where these new SOLT standards come in. While it's been a bit of a struggle even with your help, things look promising. Now based on what I have read, I would like to try a few experiments using TRL. It seems like one way to do this may be to use hardline coax to make the test fixture and cal standards.Before I go down this rabbit hole, could you have a look at that spreadsheet and give your thoughts.

author: rf-messkopf
author_rank: Regular Contributor
timestamp: March 17, 2020, 09:49:17 pm
content: Quote from: joeqsmith on March 17, 2020, 12:42:49 pmThe point of using TRL with the test board is not precision, but to place the reference planes on the PCB and to calibrate the coaxial-to-coplanar waveguide transition out. This is the reason why TRL is usually the method of choice when a calibration in a planar geometry is desired. For precision measurements at higher frequencies one would, however, not use connectors, but a probe. This also works on wafers, and is used for on-wafer VNA measurements in MMICs.You can also do TRL in coaxial geometries using airlines. This is, for example, done in metrological contexts since airlines can be manufactured to extremely tight tolerances. Moreover, in this way scattering parameters can be traced to dimensional standards, and that's what national metrology labs use TRL for. However, airlines are delicate and tedious to handle, and very easy to break. So you don't want to do TRL when you only need to calibrate to a coaxial connector unless extreme accuracy is required at high frequencies. In almost all cases you simply want a good quality SOLT/TOSM kit.Another feature of TRL: Cal standards do not have to be fully known (as opposed to OSM). For example, the line can have an arbitrary transmission coefficient (which includes loss); only the wave impedance matters. Similarly, the reflect standard can have (in theory) an arbitrary nonzero reflection coefficient (but which is assumed to be equal at each port). In fact, the TRL mathematics allows to obtain the transmission coefficient as well as the reflection coefficient from the underlying system of equations. But normally VNA firmware doesn't output them, but this could be done offline with your own software written in e.g., MATLAB or Octave. This is sometimes done in a two-tier calibration to measure wave impedance in planar geometries.There is a frequency restriction due to line length: The phase shift of the line must be kept away from 0° and 180°; for wider bandwidths several lines have to be used. Extension to low frequencies (in fact, to DC) require an additional match (this is then called TRM). Modern VNAs automatically take care of that.See the writeup here for some more details:https://www.mariohellmich.de/projects/trl-cal/trl-cal.html, and also the quoted literature.Quote from: joeqsmith on March 17, 2020, 12:42:49 pmYes, the test board shown above depends on the equality and repeatability of the connectors. Since the reference planes are on the PCB, the assumption is that the path from the VNA port to the reference plane is equal for each cal standard, as well as for the DUT connection. And this includes the connectors and the connector-to-coplanar waveguide transition.I don't think that with my test board I have too much of a repeatability issue (more a feeling than a fact) and results are fairly reproducible, but that's only up to 1.8 GHz with half decent connectors (about €8 each). For more precision and/or higher frequencies you will have to invest in 3.5mm screw-on launchers (e.g. from Huber-Suhner), be prepared to pay at least €150 each. The board dimensions must also be sufficiently accurate.Quote from: joeqsmith on March 17, 2020, 12:42:49 pmSorry, I have a ban on Microsoft Office here and can't take a look at it. But you only have to observe the phase shift restrictions with the line standards, and when using two lines allow for sufficient overlap. You can also do the math with paper and pencil. Or start with just a single line when you don't need a wide frequency band.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 18, 2020, 12:24:12 am
content: At the lower frequencies, I wonder if you really gained anything over just using the SOLT setup on that same board. I assume to made the board to run this test. Do you remember if there was any advantage?Quote from: rf-messkopf on March 17, 2020, 09:49:17 pmNo problem. If I use the numbers screened on your PCB, the spreadsheet looks like it wants two lines. One at 115.9 the other 28.4mm. It seems like a pretty big discrepancy.I was thinking with using coax, I would get better results than with FR4. I was also thinking that in the case of the attenuator, it could be built inside the coax easy enough.

author: rf-messkopf
author_rank: Regular Contributor
timestamp: March 18, 2020, 09:31:59 pm
content: Quote from: joeqsmith on March 18, 2020, 12:24:12 amI suppose you mean using SOLT elements on the PCB right in the fixture where the 0805 component under test goes. Because calibrating to the connector by a standard coaxial SOLT cal kit will not yield accurate results since the DUT is connected by pieces of transmission lines to the connectors, and these will transform.No, I have not tried to use SOLT within the fixture. That would be difficult because, e.g., the open would be undefined due to its fringing capacitance, and the load would be a resistor with unknown RF properties. In contrast, TRL does away with these problems, and allows for very precisely located reference planes right at the outer edges of the SMD pads. You will not have that level of control over the reference planes with SOLT in this situation.If you wanted to use SOLT for some reason I would rather calibrate to the connector in the usual way, and then do a port extension to the DUT in the fixture. The proper delay can be found by adding a temporary short to ground at the pads, and measuring the phase delay. A modern VNA can measure and compensate that delay automatically, and even include losses. But that will certainly have a noticeable influence on accuracy (especially phases), unless you are only interested in the S21 magnitude.As already mentioned, here the essential problem remaining with TRL is that the wave impedance of the line on the PCB is not exactly 50 Ohms, and that will affect the accuracy; you are effectively not referencing your S-matrix to a system impedance of 50 Ohms, but to 50 Ohms +/- x Ohms. But the line impedance could be measured independently and added into the cal kit definition in the analyzer for correction.Quote from: joeqsmith on March 18, 2020, 12:24:12 amOver which frequency band do you want to calibrate? And in which medium (microstrip, CPW, coax), because that will determine the relation between phase shift and frequency.Quote from: joeqsmith on March 18, 2020, 12:24:12 amThat will depend on your machining skills and your ability to manufacture resistive elements on dielectric substrates, e.g. by thin film technology, that can be put in a coaxial structure.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 18, 2020, 11:32:02 pm
content: I just used the numbers that were on your PCB and blog and plugged them in.At these lower frequencies, I have never characterized my circuit board SOLT. Running various tests over the years has never been a concern. But then again, I am only looking for ballpark numbers.I assumed with your board, you had the Short, Open, Match and Mismatch all built up on the board with the same reference. I assumed you could use the SOL to then measure the Mismatch, then use the TRL to measure the mismatch as well.The problem with the Normal SOLT standards is in my case, I would normally mount the DUT on FR4. The delay is only part of it. That's the benefit of building it all up on FR4 (or whatever medium used).I did make up a few sections of coax to try running the TRL. Even with my homemade sections, it works well enough to make some basic measurements. ***Just to add, a MWM 18GHz 50 ohm terminator measures +/-5 ohms up to 4GHz. So, I'm not suggesting this is great but for some hand made up, unmeasured sections of coax that were not even torqued, I'm amazed it worked this good.Building the attenuator into the coax would be no different than building it onto FR4. It could still all be done with surface mount parts.

author: rf-messkopf
author_rank: Regular Contributor
timestamp: March 19, 2020, 09:12:25 pm
content: Quote from: joeqsmith on March 18, 2020, 11:32:02 pmOkay, I tried that, see the attachment. I used the open, load, short and thru on the board for a standard SOLT cal, assuming that all standards are ideal, including the thru (i.e., zero delay and zero loss). Then I measured the 100 Ohms resistor soldered to the series fixture and displayed the impedance magnitude like shown in previous posts. For comparison, the same measurement is shown with the same TRL calibration as previously.You can see that the SOLT (or TOSM) trace shows quite some ripple. This is clearly an artifact and probably due to phase errors incurred by the imperfect open. But I expected it to be much worse (it will certainly get worse at higher frequencies). The phases are essential for the calculation of the impedance Z from S21, even though only the magnitude of Z is plotted, since\[Z=Z_0\frac{2(1-S_{21})}{S_{21}}.\]And, as discussed previously, you can see the line impedance being about 5% low, which means measured impedances read about 5% high. You can also see that the DUT impedance obtained from SOLT increases towards 1.8 GHz, where in reality it falls off. This is because the two parallel 100 Ohms resistors on the board that were used as the load standard for SOLT, and their resistance also falls off towards 1.8 GHz, which means that a calibration using them will show impedances too high towards high frequencies.All in all this demonstrates the advantage of TRL over SOLT in this case.Also attached is a S11 measurement of the mismatch standard on the board with SOLT and TRL for comparison.Quote from: joeqsmith on March 18, 2020, 11:32:02 pmThat's very good and surely gives confidence that TRL works for you in principle. Although using the MWM load with SOLT would most probably yield more accurate results, provided you have well corrected opens and shorts. These cables are clearly not intended to be calibration standards.Quote from: joeqsmith on March 18, 2020, 11:32:02 pmOkay, I thought you were thinking about machining a "real" coaxial attenuator like the one pictured in this forum thread:https://www.mikrocontroller.net/topic/477931#5917781. The resistive element is on the horizontal disc sitting in the groove within the cylindrical center part, and is contacted at its face side by the two pins in the attenuator and caps, which also contain the connectors. I feel like sacrificing one of my attenuators to take a look inside.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 20, 2020, 01:07:49 am
content: Thanks for running it. The results are not what I was expecting. I thought that the SOLT would show tighter grouping.I'm still waiting on the parts to try and characterize my SMA standards.I remeasured my coax and suspect this is part of the problem with my TRL. I'll recalculate the time based on the measure lengths and try it again with things torqued. You may also note I made both an open and a short for the reflection. I only tried one so there's a bit to do.For some added humor, my quick test jig to keep the coax centered. Shown with a 1206 laying in there. There's about 2mm of plastic tube between the coax and thumb screw.

author: enut11
author_rank: Super Contributor
timestamp: March 20, 2020, 07:58:25 pm
content: Just received my green 'Multi-Atten' board that looks similar to the one that @joeqsmith tested in Reply #122.NanoVNA tests compare my 20dB MicroAtten to the 20dB section on the green Multi-Atten board at both 1-300MHz and 1-900MHz.I welcome comments on what you see, especially the trace notches on my MicroAtten.enut11

author: ogden
author_rank: Super Contributor
timestamp: March 20, 2020, 09:03:52 pm
content: Quote from: enut11 on March 20, 2020, 07:58:25 pmYour 'Multi-Atten' results are so much worse compared to @joeqsmith that I suspect that there is some problem with calibration or your NanoVNA. You are advised to watch @joeqsmith youtube videos about NanoVNA, then SOLT-calibrate before each measurement to be sure that it is indeed attenuator you measure.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 21, 2020, 03:46:08 am
content: Using what I am guessing is the same model 20dB attenuator, the cables and standards that were supplied with my NanoVNA, running off battery power and sweeping from 300KHz to 300MHz.S11 (5dB/div), S21(5dB/div) and SWRAlso shown is my cobbled up shunt test jig with 1206. Like the coax TRL references, I am not expecting very good data off of these.The Keysight standards have been shipped. Rather than using components that were characterized with these standards, the plan now is to follow Mario's lead like I did with the N standards. The Keysight set doesn't have the airlines. This should at least get me to the point where I can finally use this new boat anchor to get some decent data.

author: enut11
author_rank: Super Contributor
timestamp: March 21, 2020, 06:39:20 am
content: Quote from: ogden on March 20, 2020, 09:03:52 pmThank you @ogden. After Cal, the 1-300MHz plot for my MicroAtten was much improved. Live and learn!enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: March 22, 2020, 05:24:41 pm
content: The standards provided with the Nano are obviously going to have a different reference plane than the attenuator. At least with the version of firmware I am using, I am not aware of it having a way to compensate for this.The physical length from the SMA connector to the resistor on that test fixture I show is obviously MUCH longer than with the PCB. If I use the same value resistor on both and measure them using my homemade PCB cal standards, the one mounted on the PCB would be reasonable. The other I would expect to be off by a fair amount. If it were a perfect 50 ohm resistor and everything else was perfect, there would be no return loss and the length would not matter.For fun, let's test a 1K ohm resistor. I'll stay with the 1MHz to 300MHz to avoid nanoproblems.PCB1&2 are looking at the resistor mounted to the PCB. 1) looking at the Smith chart, there's not a lot of rotation and 2) we can see the resistance is fairly flat over the entire frequency range. If we were to put say a meter of coax on the nano, we would expect to see a lot of rotation, starting at the far right and working around the outer circumference. We would expect the same with the test jig as that's what we have done.JIG1&2 are looking at the same 1K mounted in my test jig. No soldering. 1) notice that rather than a dot at 1K, we have this rotation. 2) if we calculate the resistance for this data, you can see even at 300MHz we are not even close.There's about a 40mm difference between these two setups. Using my 166ps/inch rule of thumb (obviously this is GREATLY oversimplified) we would expect about 280ps of delay.JIG3&4 notice that I have added a 340ps port extension. 3) notice that we now basically have our dot at 1K again and 4) the part appears to be somewhat flat.Keep in mind these are very back of the napkin sort of measurements, but it should provide you with some idea how important the mechanics are. I suspect after building these attenuators, you're starting to see that things are much less critical at lower frequencies.As I mentioned earlier, Mario is helping me sort out some home made standards. I made up a set that I thought would be good, but these were not even close. I machined up a new set of parts and knew Mario would not approve of them.After the third attempt, I came up with something that appears reasonable. These standards will be used at much higher frequencies and again, are just for ballparkish measurements.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 22, 2020, 05:27:15 pm
content: http://zone.ni.com/reference/en-XX/help/373153D-01/vnahelp/reference_plane/

author: enut11
author_rank: Super Contributor
timestamp: March 22, 2020, 08:28:46 pm
content: Thanks @joeqsmith.It is now obvious that HF circuits are a mixture of art and science.This has been an interesting journey for me. Starting off at audio frequencies with a nominal cutoff frequency of 100KHz, I now have great respect for radio frequency circuit designers.enut11PSWas the Smith chart named after you

author: rf-messkopf
author_rank: Regular Contributor
timestamp: March 22, 2020, 08:57:30 pm
content: Quote from: joeqsmith on March 22, 2020, 05:24:41 pmThe point is that with SOLT, for doing the vector error correction, the S11responses of the one-port cal standards as well as the S21response of the thru have to be fully known with respect to the reference plane for the connector family used.On the positive side, this means that the standards can be quite imperfect or imprecisely machined as long as these imperfections are known and accounted for, either by a model and a few parameters from which the analyzer can calculate the S-parameters of the standards, or directly by their full S-parameters (e.g. from a Touchstone file). When you are not able to determine these responses by theoretical means (e.g. an EM simulation), you can always measure them against a known cal kit.And you do not get away without corrections, at least for the open, because there will always be a fringing capacitance. Moreover, for many connector families the physical open and short will inevitably be offset from the connector reference plane. This is especially true in N connectors (look at the location of the reference plane -- in the female N connector the center pin protrudes beyond the reference plane, whereas in the male N the center pin tip is recessed).Quote from: enut11 on March 22, 2020, 08:28:46 pmWouldn't that mean he is 115 years old?

author: joeqsmith
author_rank: Super Contributor
timestamp: March 22, 2020, 10:50:15 pm
content: I feel old some days but not that old! lolQuote from: rf-messkopf on March 22, 2020, 08:57:30 pmOf course, you can't expect to use just anything for standards at 10GHz. Using an open in place of a load may not work so well no matter how you characterize it. There's a limit to how poor these can be. I believe I am pushing these limits. lol. I had read a paper that was talking about common mistakes people make when taking measurements. One of the first problems talked about how some engineers believe SOLT can compensate for bad cables. If I come across it again, I will post a link.As I mentioned, I've never done anything to correct for my home made standards. Certainly my low frequency measurements could be improved upon but they are good enough. Actually, I am not sure if I used a brand new set of top of the line Keysight standards with the Nano and the Nano supported using their compensations, would we even see any measurable difference. Part of me doubts it. I'm not suggesting that my home made standards are all that good, but we are working at fairly low frequencies with a $50 bit of hardware.This presentation goes down the VNA calibration rabbit hole pretty deep. It's a very high level talk, so nothing real complex. There are a lot of little things to consider. It's an eye opener.http://resource.npl.co.uk/docs/networks/anamet/members_only/meetings/22/juerg_ruefenacht.pdf

author: joeqsmith
author_rank: Super Contributor
timestamp: March 23, 2020, 10:48:23 pm
content: Time to break out Mario's scripts again.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 24, 2020, 09:53:57 pm
content: https://www.microwaves101.com/encyclopedias/how-to-not-trash-a-calibration-kithttps://www.microwaves101.com/uploads/Connector-Care-Poster-2007.pdfI spent some time with the microscope today inspecting the standards. Outside of a little cleaning, everything looks in good shape. I was pretty hesitant to borrow these because the finger contacts are fairly delicate. Shown are the male and female sides. These are not your 10 cent Chinese connectors we see on these attenuators.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 25, 2020, 12:54:54 am
content: Anyone who has made a set of standards that provide good results above even 3GHz, you have my respect. I'm not sure which is worse, my first attempt at the N style or these SMA ones. I had hoped that with the T-check looking as good as it did, these would be better than they are. Back to the drawing board.

author: ogden
author_rank: Super Contributor
timestamp: March 25, 2020, 06:18:35 pm
content: Quote from: joeqsmith on March 25, 2020, 12:54:54 amWell.. Yes indeed. Some time ago you were insultingly confident about "standards" shipped with NanoVNA.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 28, 2020, 05:40:03 pm
content: Still playing around with the home made standards but I thought as long as I have these Agilent standards on loan, we could try and measure the low cost 20dB attenuator with a little higher confidence.The following link is the datasheet for the Mini-Circuits VAT10 which is a 10dB attenuator:https://www.minicircuits.com/pdfs/VAT-10+.pdfAttached is the data I collected for the VAT 10. It seems to fall well within the published typical numbers.Looking at the X13773, which is the green PCB,Level 1: 10 0.8 dBLevel 2: 20 1.1 dBLevel 3: 30 1.5dBStanding wave ratio: 1.20It seems like it meets their flatness but the SWR appears higher than they claim.Also shown is a Midwest Microwave 20dB attenuator as a comparison. I don't have anything near as nice as Mario's metrology grade attenuator.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 28, 2020, 09:21:24 pm
content: Attached is looking at the same low cost 20dB attenuator after calibrating with my home made standards. Mario's scripts was used to determine the coefficients based off the Agilent standards. As you can see, there is some difference when compared with the Agilent standards.Also, as a side note, the T-check is really poor. It is based on the same hardware used to make the short and open and has roughly the same reference plane. I am using fixed resistors and suspect they are just not going to be close enough for this application.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 29, 2020, 03:30:40 pm
content: Mario was kind enough to update his Octave script to add a plot showing the phase error between the model and measured data.You can download it here:https://www.mariohellmich.de/lostfound/files/ck-modelI've attache the plots for my female SMA open and short as a reference of what to expect if you try it. Basically the steps are: Calibrate the instrument using the Agilent standards. Use adapters rather than cables. Test the short & open and collect their Touchstone files. Feed these into Marios script. You may need to change the script to support your VNAs Touchstone file. In my case the header length needed to be changed.In my particular case, Agilent has a few different stand alone editors for their database. Their newer software doesn't work with my old VNA and will corrupt the file causing a memory overflow error.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 29, 2020, 03:45:25 pm
content: This is looking at the data for my home made N standards after the third attempt at machining the parts and trimming them. These were made from an old set of Narda terminators.Also shown is the 180 degree phase difference between the open and short while sweeping up to 6GHz.For the terminators I knew I could not make anything that was going to work at these higher frequencies, so I left one of the Narda terminators stock. I have an old HP terminator that I compared it against and it seems reasonable. For the SMA I am using a part from Midwest Microwave.I have also characterized a few other bits I had to use as a sort of check. It would be interesting to see how Kirkby's would compare with my how made setup. Considering the time invested, and the advantage that I could loan these two Agilent sets, buying something ready made would be a much better solution assuming they are any good.https://www.kirkbymicrowave.co.uk/

author: joeqsmith
author_rank: Super Contributor
timestamp: March 30, 2020, 11:03:57 pm
content: Looking at the return loss of the Mini-circuit ANNE-50 and MidWest Microwave terminators.(This is after calibrating the system with the Agilent standards using an adapter rather than cables)https://www.minicircuits.com/pdfs/ANNE-50+.pdf

author: ogden
author_rank: Super Contributor
timestamp: March 31, 2020, 02:03:44 am
content: Quote from: joeqsmith on March 30, 2020, 11:03:57 pmWhich MidWest Microwave terminator (part.no) used? There are many different. I take shown Minicircuits any day - 10x lower cost yet perform better.

author: joeqsmith
author_rank: Super Contributor
timestamp: April 02, 2020, 12:31:34 am
content: To get some idea how repeatable the new set is, I had removed all of the adapters and left the VNA off for a day. I then let it warm up for an hour, installed the adapters and loaded the previous calibration file.You can see the original Touchstone files compared with the set taken today. About 0.2dB of error. The adapters I am using are not the cheap garbage like seen on that low cost attenuator, but they are certainly not metrology grade.I had a few lower cost MWM terminators. While I had everything setup, I ran all four of these. One of these I had marked suspect but it appears that two of them are are not very good.When I compare these with my home made PCB standards. These are the ones I use with the 8754A, not the ones I show with the Nano. These are using 0805s vs the 1206s. You can see up to about 500MHz, these are much better than the commercial parts. Once we get beyond a GHz, it gets pretty bad.

author: joeqsmith
author_rank: Super Contributor
timestamp: April 02, 2020, 01:15:36 am
content: A section of semi-ridged was sacrificed. Yellow tape was added to mark the direction for later. The Nano was set to sweep to 1.5GHz and calibrated using the Agilent standards. Data was then collected for the ANNE. Next the Nano was calibrated using my home made PCB standards that I use with the 8754A and again the ANNE was installed and data was collected for it. These two files were then compared against the two previous files collected with the Agilent.The Nano, when calibrated with the Agilent 85033E standards, is right in there with old Agilent VNA up to about 250MHz. As expected, at 300MHz it starts to have some trouble and at 900 it gets much worse. But again, for $50 it's pretty impressive.The graph was pretty hard to see, so I captured it at a higher res.

author: enut11
author_rank: Super Contributor
timestamp: April 05, 2020, 10:16:08 pm
content: Thanks @joeqsmith. It is reassuring to know that the inexpensive little NanoVNA can be relied on up to about 250MHz.This will also help me characterise some of my lower frequency equipment, and for only $80AUD.enut11

author: joeqsmith
author_rank: Super Contributor
timestamp: April 07, 2020, 12:22:43 pm
content: So far I've held off setting up yet another account on Tinde to order a Nano V2. I'm surprised we are not seeing any reviews for it yet as I would have thought the developers would have sent out a handful to the larger channels some time ago. It will be interesting to get one with their cal standards and cables to see how it compares. At 3GHz, the accessories should be much better than what was supplied with the Nano. The big advantage as I understand it is the V2 does not use harmonics.When you start to do more with the Nano, you may find you require additional hardware. For example, to check an amplifier you may need Bias-Ts, step attenuators, filters (for the harmonics to prevent overdriving). Bits that would normally be built into older used systems. We don't need to be concerned with filtering out the fundamental with these older systems (8753...). Pretty soon, that $80 may turn into $500.

author: ogden
author_rank: Super Contributor
timestamp: April 07, 2020, 06:50:01 pm
content: Quote from: joeqsmith on April 07, 2020, 12:22:43 pmSuch purchasing strategy does not make any sense unless you know that those 500$ worth of accessories will be used with proper instrument in the not so far future.

author: cdev
author_rank: Super Contributor
timestamp: May 24, 2020, 02:29:49 am
content: I sometimes use edge mount SMAs which terminate right at the edge of the PCB but since they are made for etched boards instead I will solder their feet to the ground plane and instead will have the trace a bit higher and use components on top or Ive also used mini coax. That seems to work really well, best of both worlds. The advantage of that kind of mucking around is that everything is reusable and rearrangeable.Quote from: David Hess on February 03, 2020, 04:41:49 am

author: joeqsmith
author_rank: Super Contributor
timestamp: June 07, 2020, 05:06:55 pm
content: I picked up a few ANNE terminators to see if I could hand select something a little tighter for my calibration kit. #1 is the part that was shown in the previous graphs. I have also included the load from the Agilent 85033E.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 11, 2020, 02:01:11 pm
content: Comparing the measurement results for the original Mini-Circuits ANNE-50+ 50ohm terminator with the last two times it was measured. This part is designated #1.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 11, 2020, 02:03:21 pm
content: Comparing all 6 pcs and finally #1, #4 and the Agilent standard.

author: ogden
author_rank: Super Contributor
timestamp: June 11, 2020, 06:55:55 pm
content: Quote from: joeqsmith on June 11, 2020, 02:03:21 pmSeems like you may return four of six terminators as faulty because specs say that upto 1GHz RL is no worse than -43dB. Why didn't you include NanoVNA "standard" in this comparison?

author: joeqsmith
author_rank: Super Contributor
timestamp: June 11, 2020, 08:42:54 pm
content: Quote from: ogden on June 11, 2020, 06:55:55 pmYou may be confusing typical with the guaranteed minimum return loss. Typical numbers are not guaranteed by the manufacture.With it's ridged design, I have no plans on ever using the terminator supplied with my Nano but was also curious. Included is the data comparing it with ANNE #3,#4 and the Agilent standard.

author: ogden
author_rank: Super Contributor
timestamp: June 11, 2020, 08:55:18 pm
content: Quote from: joeqsmith on June 11, 2020, 08:42:54 pmThank you for investing your time and effort to confirm what I told long ago inanother threadhere.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 11, 2020, 08:59:33 pm
content: Quote from: ogden on June 11, 2020, 08:55:18 pmWhat post are you referring to?

author: ogden
author_rank: Super Contributor
timestamp: June 11, 2020, 09:23:00 pm
content: Quote from: joeqsmith on June 11, 2020, 08:59:33 pmOne where I state that NanoVNA users shall consider replacing supplied 50ohm load "standard" because even 11$ "plug" like ANNE-50+ is better.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 11, 2020, 09:44:03 pm
content: You would need to provide a link to it.That said, the ANNE has a guaranteed return loss of 30dB for DC-4GHz. At 1GHz, the part that was included with my Nano is 36.5. Better than the performance that the ANNE is guaranteed for. Of course, if you have someone that can test and screen parts for you then sure.I doubt many people would be using the Nano beyond 300MHz. At these lower frequencies, the return loss for the terminator supplied with mine would be fine. The real benefit IMO is getting rid of that ridged construction.

author: ogden
author_rank: Super Contributor
timestamp: June 12, 2020, 02:49:53 pm
content: Quote from: joeqsmith on June 11, 2020, 09:44:03 pmNah. If you need it - search yourself.QuoteLOL nice try.It is pointless to nitpick guaranteed performance figure of ANNE while same graph you are reading NanoVNA figure (36.5) from, tells that both compared ANNE plugs are better, -52 and -66 @1GHz. Not to mention that spread of NanoVNA load is unknown, specs are not published and you perhaps got best NanoVNA load ever made.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 12, 2020, 03:18:17 pm
content: Quote from: ogden on June 12, 2020, 02:49:53 pmI'm not the one who brought it up or made reference to it. If you want me to read it, provide the link otherwise I will ignore it.Quote from: ogden on June 12, 2020, 02:49:53 pmLearn to read a datasheet. Making a blanket statement that using the ANNE will somehow improve the NANO's measurements over the standard that was supplied is just being naive.

author: ogden
author_rank: Super Contributor
timestamp: June 12, 2020, 05:02:56 pm
content: Quote from: joeqsmith on June 12, 2020, 03:18:17 pmWishful thinking?I rephrased it already: "I state that NanoVNA users shall consider replacing supplied 50ohm load "standard" because even 11$ "plug" like ANNE-50+ is better."QuoteLearn to use your head, if any. You can't compare datasheet figures of ANNE to nonexistant datasheet figures of Nano load standard. You have to compare apples to apples, in this case - measurements. In your data ANNE clearly wins as load standard. That's my whole point. You can't compare guaranteed datasheet figure of one device to measurement of another. That is not even naiive to say it politely.QuoteWishful thinking again. You are putting words in my mouth. When you find where I say something like "ANNE will somehow improve the NANO's measurements" - let me know.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 12, 2020, 05:53:29 pm
content: I'm not sure why you are resorting to insults. I get you like to argue but this is pretty basic stuff. Without having a means to verify the standards there is no way of knowing how you have effected the performance. It's as simple as that.

author: ogden
author_rank: Super Contributor
timestamp: June 12, 2020, 07:12:15 pm
content: Quote from: joeqsmith on June 12, 2020, 05:53:29 pmJust returning a favor.QuoteIt is you who is arguing against my statement. Already forgot?QuoteThat would be absurd for everybody to have means of comparing their standards. Funny that you chose to measure/compare NanoVNA load and ANNE terminator in 1..6 GHz range, considering:Quote

author: joeqsmith
author_rank: Super Contributor
timestamp: June 12, 2020, 08:11:23 pm
content: Quote from: ogden on June 12, 2020, 07:12:15 pmSorry you take offense to being called naive. That's not what I would consider an insult, just a fact based on your statements when you suggest I return used parts that meet the manufacture's specification. I am used to people on this forum who have little knowledge to resort to personal attacks when they have little else to use to argue their point.I'm only trying to help you understand the difference between typical and specified. Sadly, it seems your ego prevents you from learning something this basic and I suspect you will continue being ignorant and combative about the subject.I'm not sure why you would be surprised that I am assembling this cal kit for use at frequencies beyond a GHz. It was never my goal to use it with the Nano in hopes of improving its accuracy. Had I planned on continuing to work below a GHz, I would have stayed with my PCB based standards.Again, I did not buy the Nano and it has been basically been used as an educational tool. It's very low cost and simple interface make it a very good fit for learning the basics on how to use a VNA. I certainly wouldn't suggest anyone waste their money on buying a replacement terminator for it that I didn't know would improve their results.I understand that Kirkby uses sorted terminators for the standard kits he sells. It may be possible to procure just the terminators from him if you suspected the one that was supplied with the Nano.

author: ogden
author_rank: Super Contributor
timestamp: June 13, 2020, 04:38:05 am
content: Quote from: joeqsmith on June 12, 2020, 08:11:23 pmLOL no. I am not suprised at all. Initially you compared ANNE plugs in 0..6GHz range. Then after I mentioned NanoVNA load standard to ANNE comparison, for some "strange reason" you omitted 0..1GHz (of NanoVNA range) and picked 1..6GHz. Could be accident could be not. Anyway you did not manage to disprove my point - that ANNE plug is better than supplied NanoVNA load. Also please let others decide - 11$ for terminator (as load standard) which at least have datasheet figures is waste or not. Unless you show comparison in 0..6GHz range, I have nothing else to discuss with you.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 13, 2020, 03:43:51 pm
content: Quote from: ogden on June 13, 2020, 04:38:05 amSorry that the data I had collected for my one Nano terminator doesn't meet your needs. I didn't run that test for you but out of my own curiosity. I know you feel the world evolves around you and you are entitled to my time but I assure you, it's not the case. I collected that data a few months back and when you asked, I took the time to post what I had.There are no published spec's for the Nano's terminator. Each will be different (even if they were supplied by the same manufacture). However, we do have spec's for the ANNE which is 30dB return loss in the range the Nano is capable of being used. It's obvious that a person would need to measure them both if they want to know what the effects are. It's not a feeling or please let others decide but a simple fact. I can understand you not like being called out and it hurts your feelings and you feel its a personal attack and I should just agree with you. All of that has nothing to do with misrepresenting the data, especially when you start misleading the public.In singles, the ANNE will cost $15 or more. You need to consider sales tax and shipping. I imagine I could hand select a couple of 0805 100 ohm parts for the frequency range of the Nano, if it were a concern. History has shown I can't do this once I get much above a GHz and it requires a commercial part.The cost of the Agilent cal kits exceed what I would be willing to pay. I am not interested in used parts that some clueless person has damaged. Making the shorts and opens were not a simple task and required several attempts at machining parts. From the data I've shown using rf-messkopf's script and Agilent's standards, the results are reasonable. The loads are really the problem and it seems the least costly approach was to buy several and sort them.Consider they all met the manufacture's spec and can't be returned as defective. I ran 6pcs. At 11 + 0.66(tax) and say $8 in shipping, about $78. #3 also looks pretty decent. For my home hobby, good enough.

author: ogden
author_rank: Super Contributor
timestamp: June 15, 2020, 08:35:34 pm
content: Quote from: joeqsmith on June 13, 2020, 03:43:51 pmOh gimme a break. *You* are misleading public by comparing measurement @1GHz of one device to guaranteed figure @ 0..4GHz range of another.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 16, 2020, 01:38:49 am
content: Quote from: ogden on June 15, 2020, 08:35:34 pmWhat are you whining about now? You asked for the data and I provided you with what I had. I have not made any recommendations to the public in regards to buying a new terminator for the Nano. It's not my fault that you were clueless about what typical meant. Saying the part is specified to 30dB is not misleading the public. Nor is suggesting that the two parts would need to be compared to know for sure. Again, all basic things.

author: TheoB
author_rank: Regular Contributor
timestamp: January 04, 2022, 02:20:26 pm
content: Quote from: joeqsmith on June 07, 2020, 05:06:55 pmYou hand selected the best one. Isn't that the one that measures closest to 50 Ohm DC as well? For these terminators the quality of the mating surface is probably more important and I trust all those Anne terminators to work fine. After over 100 mate cycles I expect the cheap cal kit that came with the VNA to be worn completely. I have a new one (perhaps 10 times used) and see already metal chips on the connector interface (I do not clean as you showed, but I guess that needs to change). I also don't have a torque wrench.Good (and reproducible) contact is probably more important than absolute LF impedance. With a MM it's easy to determine 50 Ohm within 1%. That means the S11 would be better than -46dB. I expect the return loss to be fairly flat until ~ 500MHz. Your measurements seem to confirm that (at least for the Anne terms). I plan to simply check that the calibration remains stable. As soon as that's no longer the case, I'll invest in a new (proper) call kit and new connectors for the VNA. My usage is light (hobby).

author: G0HZU
author_rank: Super Contributor
timestamp: January 04, 2022, 02:54:44 pm
content: Some of the attempts on here to make a decent 20dB attenuator seem a bit poor to me. It's as if little thought or effort went into it.Many years a go I made a precision 20dB attenuator to use with my old 1GHz HP8405A vector voltmeter. The aim was to get very good performance to 1GHz. I dug it out and measured it the other day for someone and the plots may be interesting. The first plot to 3GHz was taken using an Ecal module to do the VNA calibration. The second plot to 100MHz was taken using precision attenuators to minimise mismatch uncertainty to a level even better than the Ecal module.I designed this using custom chip resistors measured on a 6.5digit DMM and the aim was to get as close to 20.00dB as I could with very low VSWR. It's easy to get the attenuation but it also should be achieved with very low VSWR. I think I could better this for VSWR if I made another today (better resistors available now) but the aim at the time was to get really good performance to 1GHz for the vector voltmeter.I've just measured the VSWR using a the Ecal direct at the analyser and see below for a better VSWR plot with less ripple. This shows the VSWR is extremely low and only degrades to 1.02:1 by 1GHz which was the upper frequency it was designed for.

author: TheoB
author_rank: Regular Contributor
timestamp: January 04, 2022, 05:33:25 pm
content: Quote from: G0HZU on January 04, 2022, 02:54:44 pmDon't forget that the OP was a beginner that wanted to learn. It's nice to see how he progressed with the help from several members on this forum. You step in at the other end of the spectrum to show how to build a perfectly matched attenuatorBut the OP proposed components values calculate to exactly 50 Ohm. So that's also perfectly matched (at low frequency ignoring resistor tolerances).In general you can only do this properly if you have decent measurement equipment (a reference, you have access to an Ecal, I don't even dare to ask the price).

author: G0HZU
author_rank: Super Contributor
timestamp: January 04, 2022, 05:45:23 pm
content: I was mainly referring to the efforts of others who joined the thread later offering examples of their own. The attempt on youtube by W2AEW was quite poor considering he used chip resistors and there were other poor examples in this thread.QuoteYou can make a decent 20dB attenuator if you buy the correct SMD resistors and have NO test equipment. Having a VNA or the Ecal doesn't improve the performance of the attenuator.

author: TheoB
author_rank: Regular Contributor
timestamp: January 04, 2022, 06:03:25 pm
content: Yeah of course, measuring does not affect the performance but the point was to see what the performance actually has become. Especially above a GHz you can be up for a surprise.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 05, 2022, 12:17:27 am
content: Quote from: TheoB on January 04, 2022, 05:33:25 pmExactly. It was an educational effort. They were using a scope and didn't realize it need to be terminated at 50 ohms. It took me a while to find that one. Once that was sorted out, things progressed fairly smoothly. They were experimenting at very low frequencies and we played a lot with TH parts.

author: David Hess
author_rank: Super Contributor
timestamp: January 05, 2022, 05:09:47 am
content: Quote from: joeqsmith on January 05, 2022, 12:17:27 amThe precision 1 GHz switched attenuator I have uses through-hole parts, but it is built inside a block of aluminum with machined cavities and has two tuning screws for each section.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 05, 2022, 01:32:44 pm
content: Of course, read the OPs first post to get some idea how things start out.Quote20dB target and measuring 1.5dB.... Something was obviously wrong and it was not construction.

author: EE-digger
author_rank: Frequent Contributor
timestamp: September 28, 2024, 09:58:27 pm
content: Interesting old thread. I read with my detail meter set to MEDIUM. Playing with a friend's 85053A kit at the moment and the attenuators are missing (but I have substitutes).Just wanted to add, hopefully not repeating, that Vishay's series of RF/Microwave resistors have data to 20GHz or 40GHz (I forget). The datasheet curves are by body size and by normal or flip mounting.May help someone going forward.