What VNA to get? - Page 1
Forum section: electronics / rf-microwave

author: LukeW
author_rank: Frequent Contributor
timestamp: May 11, 2018, 10:40:33 am
content: Looking at purchasing a VNA for work.What models should I look at? Any recommendations?Let's say $25k-30k AUD.Going up to 5.8 GHz would be nice, but I don't think it needs to go higher than that.Application contexts would include PCB-level RF design, and design of antenna-matching LC networks between the IC and the antenna, at frequencies that would typically be ~2.4GHz as well as ~400MHz and ~900MHz. Antenna design, antenna measurements and calculation of VSWR, and validation of PCB microstrip/CPWG widths and characteristic impedance would be relevant uses.Spectrum analysis, and analysis of transmitted RF power, and basic preliminary in-house checks for RF harmonics and regulatory compliance would be a useful use-case, too.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 11, 2018, 10:54:14 am
content: Rohde & Schwarz ZNLE6 2 Port 6GHz Vector Network Analyzer $17,720.00

author: dmills
author_rank: Super Contributor
timestamp: May 11, 2018, 11:08:03 am
content: If your working band only goes to ~2.5Ghz, you will find that you don't need to spend anything like that to get perfectly good results.I know the 8753D or even a 8753C (Which I own) is old but they still produce perfectly good results about as well as anything more modern, and I would expect to buy four with change for the cal kit(s) for that money. The real expense here is in the calibration kits and the test port extensions.If you wanted something a little classier, then a PNA should be doable, has the advantage of direct support for TRL calibration which makes the cal kit pain a bit less tedious.If you have money to burn then go for the PNA-X or such, drooool.Most VNAs do not make very good spectrum analysers, I would probably make that a separate box, apart from anything else, you want to see harmonics, which means that if your working band is 2.5GHz you want to see out to 20GHz or so, a 20GHz SA is **MUCH** cheaper then a 20GHz VNA.Have a look at folk like Copper Mountain, particularly if you are pushed for lab space, and R&S are always a good option but IMHO there is a reason the HP stuff is so popular.Regards, Dan.

author: LukeW
author_rank: Frequent Contributor
timestamp: May 11, 2018, 11:26:12 am
content: Hmmm, if I have left over budget in my proposal maybe suggestions for a spectrum analyser would be nice too

author: hagster
author_rank: Frequent Contributor
timestamp: May 11, 2018, 12:53:41 pm
content: My recommendation is to go for a Copper Mountain Compact VNA like the s5085 or cheaper s5065. They are really fast and accurate instruments and you don't end up paying a fortune for all the additional 'options'. If you have money left over you could get a E-Cal kit too.For designing matching networks give AnTune a look. It automatically calculates optimal matching networks using real component libraries in real time(takes a live S11 feed from the VNA)http://www.antune.net/index.htmlAs others have said you are best to go for a separate Spectrum Analyser. I have played with a Signal Hound one recently and it seemed pretty good.If you really need an all-in-one VNA/SA the Keysight Fieldfox might be worth a look.

author: LukeW
author_rank: Frequent Contributor
timestamp: May 11, 2018, 01:35:03 pm
content: The Copper Mountain Technologies S5085 looks nice, but I'm generally a bit skeptical about all PC-based instruments.I've never used a PC-based VNA before, but all PC based scopes and stuff generally seem a bit crap, and just not as good as the "real thing".I'd like to do the job properly, with a real good tool, and if I need to spend a few extra bucks that's OK.Would also like recommendations for SAs (like ~$3000 I suppose?) if anybody has a favorite they want to suggest.

author: dmills
author_rank: Super Contributor
timestamp: May 11, 2018, 03:32:05 pm
content: I second the slight twitchyness about PC based instruments, USB based things doubly so.It can work, but I am not sure I like random USB cables with what may or may not be adequate isolation in my RF lab.Copper mountain does however have a decent rep, and if you are happy with that operating style and the box does what you want, then why not?As to spectrum analysers, the usual suspects really, Keysight, R&S, Anritsu all got decent gear with slightly different operating styles, all of it is fine.One figure of merit sometimes ignored (especially by the PC based instrument vendors) is sweep rate, and in the case of FFT IF based designs the maximum bandwidth for which POI is 1, especially when working with digital modes, being able to set peak hold and capture the third harmonic of an entire channel with high POI is a very useful party trick.Having a quasi peak detector and a 9KHz RBW option is useful if you ever want to do precompliance testing.Regards, Dan.

author: hagster
author_rank: Frequent Contributor
timestamp: May 11, 2018, 04:08:34 pm
content: Quote from: LukeW on May 11, 2018, 01:35:03 pmI have used some crappy PC based scopes too. CMT is in a different league.You can download their software for free. It has a demo mode which I can vouch for being near identical to the real thing.Most of these companies will lend you a demo unit to evaluate if you ask nicely btw.

author: w2aew
author_rank: Super Contributor
timestamp: May 11, 2018, 07:48:18 pm
content: The 6GHz Tektronix TTR506A is about $12k - it also runs a PC-based user interface similar to the Copper Mountain units.https://www.tek.com/vna/ttr500Software available for free to try as well.There is a LE option (slightly lower performance) 6GHz unit that lists for just under $6K US. See the bottom of the above webpage.

author: KE5FX
author_rank: Super Contributor
timestamp: May 11, 2018, 08:27:16 pm
content: Quote from: LukeW on May 11, 2018, 01:35:03 pmIf you buy a new benchtop VNA today, you're going to get a PC-based instrument whether you want one or not. It would be crazy to build one any other way.So it's just a question of whether it uses your PC or theirs.... and how much you pay for it.

author: hagster
author_rank: Frequent Contributor
timestamp: May 11, 2018, 09:31:51 pm
content: We had a 40GHz HP VNA that ran WinNT on a really old embedded PC. While you can connect it to the network. It was basically a huge honey trap of unpatched vulns. We could have upgraded it to WinXP, but the involved replacing the motherboard and the front panel.

author: dmills
author_rank: Super Contributor
timestamp: May 11, 2018, 11:23:10 pm
content: True that everything is a PC these days, been that way for a while, but you live and die on the user interface, and I rather like having buttons and encoders even if the underlying compute platform is a PC.Regards, Dan.

author: KE5FX
author_rank: Super Contributor
timestamp: May 12, 2018, 12:22:45 am
content: Interestingly, musicians have already solved this problem by using MIDI to separate their control surfaces from their instruments. Someday we may see gadgets like this:... for PC-based network analyzers, spectrum analyzers, oscilloscopes, anything bigger than a DVM.

author: G0HZU
author_rank: Super Contributor
timestamp: May 12, 2018, 12:50:22 am
content: I guess the used choice in this price range would be something from the Agilent E5071x range. Typically covering 9/300kHz to 8.5GHz. These big old VNAs have a fairly good user interface (apart from the cal kit setup) and are set up to be easy to use remotely, especially in an ATE or manual test environment. The RF performance is generally very good and the measurement speed is quite good. But they are getting quite old now and still command high used prices although the prices vary a lot from seller to seller. We have several of them at work and they have been quite reliable over many years. I've only seen one fail and go back for repair and I'm not aware of any others that have failed like this. Note: the display on the B version is only VGA but it is still useable. I think the C version offers 1024x768. It is possible to get higher res modes on the B version with an external monitor but this is fiddly to set up.I would naturally shy away from any RF test gear made by Tektronix for various reasons. But if you are buying a new piece of gear from them I'd check out the long term cost of maintaining it under a service contract. Check out what happens if/when you leave the $$$ contract. How much will it cost you for Tek to repair your faulty VNA in 5 years' time? I also watched Tek's own youtube videos of the TTR500 series VNA and I'm not impressed.The Copper Mountain VNAs look to be a class above but I've not played with one so I can't be certain. I was offered a demo of any CMT model I chose via a UK rep (think it was Melcom) but this will have to wait for a less busy time at work.The little Pico VNA is another unknown but seems remarkably cheap for a 2 port VNA. It is very basic with a very dodgy looking GUI but it might be good enough for your needs although the limited range for the RF source power would be a deal breaker for me.

author: LukeW
author_rank: Frequent Contributor
timestamp: May 12, 2018, 10:06:22 am
content: A self-contained system which does not need to connect to a separate PC would be better, because (among other reasons) I use a Mac and Linux machines, and usually avoid Windows unless it really can't be helped or can't be run inside VirtualBox.

author: tszaboo
author_rank: Super Contributor
timestamp: May 12, 2018, 10:31:47 am
content: Quote from: hagster on May 11, 2018, 09:31:51 pmSo, connect it to a firewall? For about 100 EUR there are mini PCs that have 2 or more Ethernet ports, and any semi-competent network administrator can setup something like that.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 12, 2018, 10:53:08 am
content: or not connect it at all. i dont get a reason why we have to when we can sit there and do the job...

author: dmills
author_rank: Super Contributor
timestamp: May 12, 2018, 11:49:04 am
content: Some form of connection to a PC is extremely useful, be it Ethernet, GPIB, USB or RS232 so that you can use tools like softplot and for automated measurements.But yea, working assumption is that the OS is full of holes so treat appropriately.Regards, Dan.

author: hagster
author_rank: Frequent Contributor
timestamp: May 12, 2018, 12:07:57 pm
content: The network connection is useful when you need some kind of automation or remote control. I often have a need to control a signal generator form a different room for instance.Also if you need to do documentation its really handy to have screnshots of data files ready to embed in a document. Yes USB and floppy disks work, but its clunky.Portability is a big thing for me these days too. Being able to move the instrument to the DUT rather than visa versa is awesome.

author: Omicron
author_rank: Regular Contributor
timestamp: May 12, 2018, 01:51:32 pm
content: Quote from: LukeW on May 12, 2018, 10:06:22 amI'd cast another vote for the R&S ZNLE6. I've played around with one and the UI is way better than the TTR506A which I found confusing. You can use Windows Remote Desktop to control it from a Mac using the official RDP client for OSX from Microsoft, I've done so and the UI adapts itself to that mode and is not limited to the resolution of the built in lcd so you can run it full screen on whatever monitor you have hooked up to your Mac. It also automatically adds the buttons that are normally on the front panel of the device to the GUI when running via RDP. I was really impressed on how polished it all is. Definitely ask R&S for a demo before you decide.

author: G0HZU
author_rank: Super Contributor
timestamp: May 12, 2018, 02:41:31 pm
content: I looked over the specs for the ZNLE6 and the source power can only be varied over about -10 to +2dBm typical. This alone would be a dealbreaker for me. I'd want to be able to vary the source power well below -30dBm. The other specs don't look that great but it is a low cost entry level VNA so there will be compromises in terms of price vs performance.I'd suggest it is best suited for general purpose passive work where accuracy isn't critical. Where I work, few people would want to use this instrument unless it was for casual research work and all the other VNAs were in use already. So we would be unlikely to purchase one if we had one on trial.

author: hagster
author_rank: Frequent Contributor
timestamp: May 12, 2018, 03:38:35 pm
content: So what are some of the features that people value in a VNA?I find TDR and Time Gating to be handy.

author: PnpNpn
author_rank: Contributor
timestamp: May 12, 2018, 09:26:15 pm
content: +5 für den deutschen Tiger, No need for maintenance

author: G0HZU
author_rank: Super Contributor
timestamp: May 14, 2018, 10:53:14 pm
content: QuoteI don't think the ZNLE-6 VNA qualifies for this if you want to do any basic amplifier design or verification. It appears to be crippled by its limitations wrt the source power and the signal handling of the receiver port.If you set the source as low as it can go (-10dBm) and them put a 15dB gain LNA inline for test it will overload the VNA receiver as the receiver max level appears to be 0dBm. So it is not really suitable for full s2p tests on a basic LNA that other VNAs can do easily. It really does look to be optimised (crippled?) for passive testing. If you want a decent/versatile lab VNA for active and passive work I'd run a mile from the ZNLE-6 based on the datasheet specs alone.It's a shame that gear like this doesn't get sent out for independent (critical) testing because otherwise you are at the mercy of the marketing dept of each manufacturer unless you get one on trial for your own evaluation.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: May 14, 2018, 11:45:56 pm
content: It's not a bench instrument, but consider the Keysight Fieldfox. It can be upgraded from VNA to VNA+SA using a license key. The portability comes in handy when doing antenna tests and such. The one thing I don't like about it is the relatively low-res display.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 14, 2018, 11:46:43 pm
content: Quote from: G0HZU on May 14, 2018, 10:53:14 pmuse attenuator (such as 6 - 20dB attenuator) on the output of LNA. recalibrate beforehand with the attenuator attached.

author: hendorog
author_rank: Super Contributor
timestamp: May 15, 2018, 09:49:19 am
content: I know you don't like PC instruments, but...If it was my money, I'd squeeze the boss a bit more and get one of the Copper Mountain VNA's, an eCal kit and the new SignalHound 20GHz SM200A.That is a heck of a lot of capability for your money.Or get one of the bench VNA's mentioned, a cal kit, and a Siglent SSA3000X series Spectrum Analyser with the change.

author: G0HZU
author_rank: Super Contributor
timestamp: May 15, 2018, 08:05:07 pm
content: Quote from: Mechatrommer on May 14, 2018, 11:46:43 pmThe problem with adding attenuators inline is that it degrades the quality of reflection measurements when making full s2p measurements after a full SOLT calibration (with the attenuators in place). So including attenuators like this is a bit of a fudge at best. It gets worse if you try and do something as mundane as trying to measure a classic s2p model of a simple BJT in common emitter. The -10dBm drive level from the VNA will be too big by maybe 20dB and will cause distortion effects in a typical small signal BJT biased at a few mA.The other limitation of the ZNLE-6 is the linearity of the receiver. It appears to have a spec of 0.3dB (compression?) between input levels of -5 to 0dBm as the max input level of 0dBm is approached. The typical spec here is 0.2dB which is slightly better but all this points to a VNA that is really meant to be used for basic testing of passive parts with the drive level set at -10dBm.It will be OK for some users but most RF designers will want something more versatile. I couldn't live with it.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 16, 2018, 01:55:09 pm
content: Quote from: G0HZU on May 15, 2018, 08:05:07 pmuse 20dB attenuator on the input of small signal bjt. recalibrate beforehand with the attenuator attached. i've done this (attenuators at both input and output) to get a descent S21 measurement, and as workaround of VNA IO impedance mismatches... well... i'm not arguing your points i'm just suggesting workarounds. you maybe right, if OP can spend a little bit more, he can find better VNA. ymmv.

author: Omicron
author_rank: Regular Contributor
timestamp: May 16, 2018, 04:36:22 pm
content: If you're doing amplifier design then the ZNL is probably the one to buy if shopping for an entry level R&S instrument. The ZNLE is a ZNL without any of the options and without the possibility to install any after purchase. The ZNL offers an option to control the source down to -40dBm along with various other things.For myself the ZNLE is pretty much the ideal device. I don't do transistor level RF design. My uses for a VNA are antenna matching for various wireless modules (ISM, Bluetooth, ...), basic evaluation of antenna gain and some PDN related measurements for evaluating decoupling performance. Since RF is not my main focus I need something that is easy to use and works reliably without much fuss. When I do dabble with active circuits it's more for self education than professional use and the workarounds for the source limitations are acceptable.The PicoVNA works well for me but I hate the user interface. The ZNLE is a stretch in terms of price but in comparison it is a pleasure to use.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 16, 2018, 08:31:16 pm
content: Quote from: Mechatrommer on May 11, 2018, 10:54:14 amRohde & Schwarz ZNL6 2 Port 6GHz Vector Network Analyzer $25,565.00for additional $8000, you get few more dB dynamic range, and... more attenuation on the output (add another $2,470 for Rohde & Schwarz ZNL6-B22.02 Extended Power Range for ZNL6), maximum input port is still 0dB. ymmv..

author: G0HZU
author_rank: Super Contributor
timestamp: May 16, 2018, 08:57:50 pm
content: In a business environment it's worth the extra money to get the control of the source power and to have the ability to fit options to it. It looks like the ZNLE-6 is deliberately crippled and that was the impression I got from reading the specs. It will be OK for some users but it will never be a versatile VNA unless there is a way to 'uncripple' it.QuoteOK, but I can only offer advice in general. Assuming the instrument would be used for semi serious RF design the 'workarounds' suggested by Mechatrommer just won't deliver good performance. The suggestion to use a 20dB attenuator inline with port 1 when doing a full 2 port calibration isn't realistic. You can get away with a 10dB attenuator if noisy/degraded data is acceptable but how is the VNA going to do a valid SOLT calibration when looking through a 20dB attenuator? The unterminated return loss of a typical 20dB attenuator (with a short or open) could be similar or better than the reference 50R load at some frequencies in the GHz region. How is the VNA going to cope with that?You ideally want to be able to measure S11 S12 S21 and S22 in one go (after a valid calibration) and then generate a valid s2p (S11 S12 S21 S22) data model of the device under test and that is the main function of a full 2 port VNA.

author: PnpNpn
author_rank: Contributor
timestamp: May 16, 2018, 11:01:56 pm
content: Dear G0HZU,let me ask you, I have some technical questions, write me private messages.I do not want to clog a topic. Thanks!Quote from: G0HZU on May 16, 2018, 08:57:50 pm

author: G0HZU
author_rank: Super Contributor
timestamp: May 16, 2018, 11:46:43 pm
content: Hi PnpNpn,I don't wish to appear rude but I turned my PM feature off a long time ago. Sorry about this...Besides there is no 'one size fits all' answer to this thread in case anyone doesn't agree with my view. For some people the ZNLE-6 will be a good choice. Others will want the more compact Pico VNA or a Copper Mountain VNA etc etc.I chipped in to help people make a more informed choice because for users like me, the ZNLE-6 is a non starter because of the limitations it has with the source power and the linearity of the receiver. These limitations limit it mainly to the testing of passive networks in my opinion.

author: Omicron
author_rank: Regular Contributor
timestamp: May 17, 2018, 02:55:27 pm
content: Quote from: G0HZU on May 15, 2018, 08:05:07 pmWhere did you find that number? I see one mention of 0.3dBm in the section "Test Port Input" but it refers to +10dB to +5dB input level, not -5dBm to 0dBm. Am I misinterpreting something?

author: G0HZU
author_rank: Super Contributor
timestamp: May 17, 2018, 09:54:16 pm
content: The +5dB and +10dB are power ratios referenced to a source power of -10dBm so that equates to input power levels at the receiver of -5dBm and 0dBm.

author: Omicron
author_rank: Regular Contributor
timestamp: May 17, 2018, 11:46:30 pm
content: Ah, I see!To get a sense of what these design compromises in the ZNLE mean in the real world, I made a measurement of a Crystek amplifier I had laying around. The data-sheet for the device can be found here:http://www.crystek.com/microwave/spec-sheets/amplifier/CRBAMP-100-6000.pdfI used a 20dB attenuator in the source path (port 1) and for the rest pretty much the default settings of the instrument. I would say that certainly below about 4GHz there is good agreement with the graphs in the data-sheet.

author: G0HZU
author_rank: Super Contributor
timestamp: May 18, 2018, 12:36:05 am
content: You've selected a fairly meaty amplifier there that can cope fairly well with -10dBm drive at its ports. Try doing it with something like a low power, high gain LNA running at 3V biased at a couple of mA.A really simple and classic 'active' task would be to measure a small signal s2p model of a jellybean BJT transistor biased at a few mA. i.e. produce a data file for S11 S12 S21 S22. A VNA designed for active circuits can spit out a small signal s2p file in a few seconds with the source power set down low enough to preserve linearity in the DUT and the VNA. I don't see how you can easily do this with the ZNLE-6 even if you do it in stages with attenuators inline for some measurements.Note that even R&S state in their brochure that the ZNLE-6 is a VNA designed to be able to make bidirectional measurements on passive components. The specs scream out that this VNA is crippled in this respect.Can it be hacked to 'decripple' it?

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 18, 2018, 12:58:34 am
content: Quote from: G0HZU on May 18, 2018, 12:36:05 amany recommendation on VNA model that can do the job?

author: KE5FX
author_rank: Super Contributor
timestamp: May 18, 2018, 01:05:50 am
content: Quote from: Mechatrommer on May 18, 2018, 12:58:34 amWhat I'm seeing in this thread is a lot of people talking about $30K instruments that can't do what a 20-year-old HP 8753C can do at 1/10 the price.So I'd say that's a pretty strong hint, especially for those who prefer non-PC-based instrumentation. HP VNAs are what all those other companieswishthey were building.

author: JohnG
author_rank: Frequent Contributor
timestamp: May 18, 2018, 01:08:08 am
content: The PicoVNA certainly bears a strong resemblance to this:http://latechniques.net/wp-content/uploads/Dw97049_Brochure_LA19-13-03.pdf.Is it's software really that bad?Thanks,John

author: G0HZU
author_rank: Super Contributor
timestamp: May 18, 2018, 01:13:15 am
content: Yes, the full 2 port 8753 VNAs are fabulous instruments, even today. We still have quite a few 8753ES models at work in the main design labs even though they must be about 18 years old. If I wanted a general purpose 6GHz VNA and also wanted best bang for buck I'd go for the older HP8753D model. The prices for these are tumbling and I'd much rather have a £1500- £2000 HP8753D than the ZNLE-6.But the HP8753C can be had for even less money. However, the OP did seem to want to spend a lot of money... $25k?

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 18, 2018, 01:34:00 am
content: I wouldnt dare investing big money on obsolete model unless there is strong assurance it will run ok for a long time. But i dont mind buying it at small money with slight damage. If i can fix it i saved alot of money, if not, i lose small amount of money. But that is me, ymmv. I think mathematical model of current technology is good enough to 'de embed' system's respond or characteristic. So when attenuators are included in calibration, they are considered in-system elements and de -embedded from final dut result, hence not necessitating of low signal vna output and high input signal level for the purpose mentioned. I read briefly on this 'de embedding' in app notes, agilent/keysight iirc, but not really 100% sure understand since i have no intention at designing a vna, and the math is a bit daunting. Ymmv.

author: KE5FX
author_rank: Super Contributor
timestamp: May 18, 2018, 01:37:11 am
content: Quote from: G0HZU on May 18, 2018, 01:13:15 amI would be only too happy to sell him mine for that.

author: Omicron
author_rank: Regular Contributor
timestamp: May 18, 2018, 07:36:50 am
content: The ZNLE is not a 30K instrument. Not even half that price with the discount R&S gives you (at least here in Europe). 20 year old second hand gear might be great for hobby but for professional use it is simply not an option. At least not in my shop. I want equipment that has support and warranty.I don’t dispute that the ZNLE isn’t meant to measure active devices, R&S is pretty clear about that in their documentation. I just wanted to provide a feeling of what that limitation means. I don’t do transistor level design so I can’t easile do a sample measurement in that respect unless someone is willing to send me a DUT.Don’t discount practical issues either. When I do antenna measurements I take the entire setup outside since I do not have an anechoic chamber. With an instrument like the ZNLE that is trivial, you can carry it in one hand. Try that a few times with a classic HP and let us know how much fun that is :-)

author: palpurul
author_rank: Regular Contributor
timestamp: May 18, 2018, 07:49:54 am
content: How about second-hand equipements?Keysight's ebay storehas some good VNAs. Most of them are pretty old have still floppy disk drivers, butthis onelooks pretty modern.

author: hagster
author_rank: Frequent Contributor
timestamp: May 18, 2018, 07:58:38 am
content: I agree, The software looks identical and LA Technologies sells an OEM module.Looking in more detail at this PicoVNA specs and features, it does seem to offer plenty of bang for your buck. There is some useful discussion of this device herehttps://www.eevblog.com/forum/testgear/picovna/25/It sounds like the software really is that bad though (VB6 in 2018), but like the Copper Mountain it has a demo mode.Quote from: JohnG on May 18, 2018, 01:08:08 am

author: Omicron
author_rank: Regular Contributor
timestamp: May 18, 2018, 08:41:19 am
content: Quote from: JohnG on May 18, 2018, 01:08:08 amLooks like the same unit and software, although it seems to have more of the intermediate connections available on the front panel offering some additional flexibility.You can download the software from the Pico website and try it out for yourself. You can certainly make do with it but the product could have been so much better if they had invested a bit more in the software.

author: PnpNpn
author_rank: Contributor
timestamp: May 18, 2018, 01:20:26 pm
content: Hi G0HZU,how can I contact you and hear some tips.Quote from: G0HZU on May 16, 2018, 11:46:43 pm

author: G0HZU
author_rank: Super Contributor
timestamp: May 18, 2018, 02:37:15 pm
content: QuoteI had a look at one of our HP8753ES VNAs at work and it has a 1999 date code. I still feel a bit of a tingle when I use one of these old VNAs because I know they are so special. I think we have three or four of them in the main design labs and I think we have owned them all from new. They aren't as popular these days because of the grainy and gloomy VGA display and the lack of modern I/O but for users like me this doesn't really matter as I mainly use a VNA as a means to grab 'n port' data models to export to a PC.One thing to watch out for with the ENA E507x series of VNAs from Agilent is that they generally don't have bias tee ports at the back of the instrument. We have a few of them in the ATE/production area and I don't think any of them have bias tee connections. I think it's an option and this tends to push up the used prices of something like an E5071C that has the bias tee option. They do seem to hold their prices really well if they have the desirable options.

author: G0HZU
author_rank: Super Contributor
timestamp: May 18, 2018, 02:39:32 pm
content: Quote from: PnpNpn on May 18, 2018, 01:20:26 pmNot sure what you mean but the best thing to do is start a thread on the forum. Virtually everything I say on RF forums gets dismissed by at least one or more 'experts' despite me spending all my career doing RF work. So you are probably asking the wrong person anyway

author: kg4arn
author_rank: Unknown
timestamp: May 18, 2018, 04:27:31 pm
content: @ G0HZUI, for one, follow your posts and appreciate your insights.Thank you

author: KE5FX
author_rank: Super Contributor
timestamp: May 18, 2018, 09:42:53 pm
content: Quote from: G0HZU on May 18, 2018, 02:37:15 pmThose Sony color displays sucked when they were brand new. It's hard to exaggerate how awesome an 8753C/D/E model looks with the SimmConn 1024x768 LCD. It is worth replacing a perfectly-good CRT with one.

author: hendorog
author_rank: Super Contributor
timestamp: May 19, 2018, 12:39:43 am
content: Quote from: G0HZU on May 18, 2018, 02:39:32 pmFWIW, you are one of the guys that I take notice of when you post, and I value your comments highly. You generally post something I didn't know before or didn't think of. If it is something I did know already or worked out for myself then I feel quite chuffedI think it is a bit on the nose for people to be asking for personal help by PM. The whole point of this forum is to post openly.

author: Omicron
author_rank: Regular Contributor
timestamp: May 19, 2018, 11:10:18 am
content: Quote from: G0HZU on May 18, 2018, 02:37:15 pmI'm assuming that if you don't have internal bias tees and use external ones you run into similar issues with S11 and S22 measurements then when you use external attenuators? Would it be as big a deal breaker not to have them when selecting a VNA as the source attenuation? It's interesting to know because all these things tend to be options you have to pay extra for so there is some kind of price/usefulness consideration. Do the internal bias tees even make sense on low end devices like the PicoVNA and the TTR506A or are they more of a gimmick considering the performance limitations of the VNA itself?

author: G0HZU
author_rank: Super Contributor
timestamp: May 19, 2018, 12:09:07 pm
content: First, thanks for the kind comments from kg4arn and hendorog.Getting back to VNAs and bias tees I can only offer my own experience of what I do and what I see at work...QuoteAt work, built in bias tees don't get used very often unless there is a doubt about a manufacturer's S2p data or the data doesn't cover enough frequency range. Then they can be useful if a transistor or MMIC needs to be measured. They can also be useful when testing something as simple as a biased diode. However, it is something that all RF engineers should try and do now and again just for the experience. I've also used external bias tees many times and calibrated them out. Other times it's possible to be sloppy and just bias the device directly inside the test fixture. I see this a lot at work and it's often OK to do this especially if the same bias network is being used in the real design anyway and the aim is just to get an s2p model of the circuit rather than the active device alone.I have usually had very good results with (fairly basic) external bias tees up to a few GHz. I think it's more important to have the source power control than internal bias tees but I guess it depends on what type of device gets tested most often and over what frequency range. External bias tees are usually going to misbehave up at many GHz especially if the cable and bias tee are moved during calibration etc. So this will degrade the results.I don't have any experience of using the USB VNAs like the Tek or the Pico so I don't know how well they perform when measuring active parts. The specs for the Tek don't look that good to me and the Pico VNA doesn't have much range on the source power control. They are both probably fine for most investigative tasks, however and it would be interesting to see how well they can measure s2p data of active devices using the bias tees. I expect them both to struggle with critical measurements but I don't think they are designed for stuff like that. It's all about compromises in terms of size, power, weight and cost as I'm sure we will all agree.

author: Omicron
author_rank: Regular Contributor
timestamp: May 19, 2018, 12:18:36 pm
content: Well these are low cost devices after all so they are certainly not meant for critical measurements in an RF lab. If there is an interest, I have access to both a PicoVNA and a R&S ZNLE and could perform some measurements to evaluate their performance. I've only used these for antenna measurements though and transistor level RF amplifiers are a bit outside my comfort zone so I'd need someone to volunteer a DUT and some guidance as how to best set things up.

author: G0HZU
author_rank: Super Contributor
timestamp: May 19, 2018, 12:29:06 pm
content: Edit: I think we double posted but I had a go at making a quick and dirty amplifier that would have similar properties as the Crystek MMIC amp (back in post #36) and I've listed the results below.The aim was to simulate and predict the performance using the manufacturer's S2p data for my MMIC (in my case I used and old SBB-5089Z) and a simulation of the PCB layout using Genesys and Sonnet. Then compare it (using a VNA) to a measurement of the real circuit built on a PCB. It's possible to design the circuit and PCB in Genesys and then export it all to Sonnet to simulate the PCB layout. I find this setup works really well.The Genesys plot below shows the simulation data for S21 and S12 and also the imported data of the real PCB with a real 5089Z MMIC on it. i.e. the VNA was used to compare/confirm the simulation.There's a plot showing the input VSWR for both the real PCB and the simulation and you can see they agree quite well. The two green traces almost overlay perfectlyHowever, I did cheat a bit because my simulation only goes to 5GHz and not 6GHz. At 6GHz my bias choke has a slight resonance and it spoils the comparison. I don't have an accurate model of the bias choke at 6GHz so I cheated and cropped the data at 5GHz.I've also included an image of the real PCB when it was being tested on the VNA. This is a quick and dirty test PCB milled on some 0.031" FR4 material.The results agree very closely and this is partly due to the accuracy of the manufacturer's s2p data for the 5089Z MMIC.

author: Omicron
author_rank: Regular Contributor
timestamp: May 19, 2018, 12:44:04 pm
content: That kind of CAD software is well out of my reach, I see why you would want a VNA with matching capabilitiesIt does provide a good baseline for comparison though. Would you be willing to send me the test board? I could measure it on the low end devices and send you the touchstone files. We could then see how they fare.

author: Antonio84e
author_rank: Contributor
timestamp: May 19, 2018, 08:58:28 pm
content: consider MegiQ for affordable and easy to use VNAs:https://www.megiq.com/

author: G0HZU
author_rank: Super Contributor
timestamp: May 21, 2018, 01:06:57 am
content: Quote from: Omicron on May 19, 2018, 12:44:04 pmSadly, the board is a bit of a scruffy mess and it has some expensive connectors on it so I don't want to part with it. Plus I want to try and scavenge a decent wideband choke at work next week and some lower loss caps to get it to work with a smooth response up to 6GHz.The circuit is really simple and the results should be predictable. If you look at the datasheet for the SBB-5089Z there is an application circuit and PCB layout. My results are very similar to the datasheet. Your S11 plot for your Crystek amplifier looks a bit ripply. Maybe try doing just a 1 port cal directly at the VNA port 1 and try measuring S11 without a cable? Simply terminate the output of the amp in a decent SMA 50R load. I'd expect the S11 result to be a bit like my MMIC board in that the response curve and the dip should be smooth (rather than ripply) but then I can only guess at what is inside the Crystek module.

author: borjam
author_rank: Unknown
timestamp: May 21, 2018, 07:43:21 am
content: Quote from: NANDBlog on May 12, 2018, 10:31:47 amOf course. Now think that it's not the only untouchable sacred cowManaging that can be a nightmare.

author: Omicron
author_rank: Regular Contributor
timestamp: May 21, 2018, 08:28:14 am
content: Quote from: G0HZU on May 21, 2018, 01:06:57 amYes, the ripples in my previous measurement are caused by my carelessness in doing the measurement and possibly because I don't have really good cables. I re-measured as you suggested using only an adapter to connect the amplifier. I measured without the 20dB attenuator first and stored that to memory (the blue trace). This trace is quite similar to your results. Then I repeated with the 20dB attenuator in place (after recalibration obviously). This results in the yellow trace. So you can definitely see the difference. Some waviness is added that I couldn't get rid of with calibration. When I measure the distance between the ripples this is about 2.1GHz. This, I believe corresponds to roughly 5...6 cm which is indeed in the ball park for the length of the adapter + attenuator I used.In full disclosure, I used a ZNL for these measurements as that's what I have access to. The hardware is identical to the ZNLE though. The service manual for these is available from R&S (you do have to register). Looking at it both the ZNL and the ZNLE use the same RF board, exact same part number. In fact there doesn't even appear any provision for the optional source and receiver attenuators that you can get for the ZNL. I'm guessing these are already on the board. Curiously they can't be activated by just a software key, you need to send the device back to R&S for re-calibration. I think that might also be the only difference between the ZNL and the ZNLE: the way they calibrate the instrument (slightly better tolerances on the ZNL?).

author: Wolfgang
author_rank: Super Contributor
timestamp: July 31, 2018, 09:55:12 pm
content: Hi,I have an Anritsu MS2036A portable and a Keysight E5071C 2-Port 8.5GHz. The Anritsu is small, but absolutely no fun at the bench.The E5071C is an old-fashioned boatanchor, but- It works without a PC and has a large display- Its more accurate and has better dynamic range that a lot of other VNAs- You can measure frequency translating devices, too (paramps, mixers, ...)- SCPI controllability is very good- Its not buggy like newer stuff.- You can write extensions to the installed software, because its Windows based. Visual Basic is old-fashioned, but powerful.- There is a lot of support on the web, docs and utility software.The downside: you have to negotiate *a lot* to get a reasonable price for it. Something in the range of 40% discount should be possible.Some measurements with frequency offset mode:https://electronicprojectsforfun.wordpress.com/parametric-rf-amplifiers/a-parametric-upconverter-for-the-40m-band/

author: clockspectrum
author_rank: Contributor
timestamp: August 01, 2018, 08:14:59 pm
content: The desktop units can be large, but I sure love mine! Ive used a E5071C at a time where all I had was an older 8753ES. It was a large improvement in usability compared to the older stuff. I think its a great analyzer for the money. Ive ended up upgrading to a N5221A and love it. I will say that you should make sure you invest in a good calibration set and possibly cables depending on what kind of measurements you are making, otherwise you will be pulling your hair out.Matt

author: Wolfgang
author_rank: Super Contributor
timestamp: August 01, 2018, 10:53:05 pm
content: I agree. Without a proper cal kit and reasonably phase stable cables all the possible accuracy is gone, especially above a GHz or two.I use an N cal kit from Anritsu, an SMA cal kit from Dr. Kirkby, and finally a Keysight e-cal module (I got too lazy).Good cables are Sucoflex 104 or the thick, big as a hotdog-sausage-type phase stable ones from Gore or Keysight. They are unwieldy but accurate.