How do the features in old VNAs and SAs differ from new ones? - Page 1
Forum section: electronics / testgear

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: March 09, 2024, 12:43:09 am
content: Hello,I've been slowly researching VNAs and SAs because I'll need them. I'm looking to buy used, and, aside from the more obvious specs, such as BW, noise floor, etc, I wanted to know if there are any "killer features" or important improvements that have been done since time immemorial that would hamper ones ability to use these old VNAs and SAs for serious analysis/work? Alternatively, is there something you find particularly helpful that is missing from such aged equipment?Thanks!PS: I'm intentionally intending *not* to get a Tiny SA or similar. Please don't suggest these options. But you're welcome to point out how much better they are than older, used, equipment.

author: tautech
author_rank: Super Contributor
timestamp: March 09, 2024, 12:52:53 am
content: Actual requirements and budget would be a good place to start.

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: March 09, 2024, 01:46:50 am
content: Budget, about 3K USD for the used SA should net me a 5Ghz or greater one. The VNA will be more. Not that I want to spend more, but I'm looking at about 4K minimum for a 5GHz capable VNA.Actual requirements (Please understand that this is a work in progress.):At present, I'm working on developing a wireless device. It will operate via wifi, or via the ISMhttps://en.wikipedia.org/wiki/ISM_radio_bandband (which is the preferable option). So I'm looking to obtain equipment that will enable me to see the output power and performance of the device. At the very least, I will have to make a custom antenna for the device and characterize it's performance.I also hope to design/build my own oscilloscope. So, I'll need equipment to do that. I'd like to break the GHz barrier with my custom scope.

author: xrunner
author_rank: Super Contributor
timestamp: March 09, 2024, 02:08:20 am
content: Quote from: ballsystemlord on March 09, 2024, 01:46:50 amI have one of the newer "modern" spectrum analyzers, a Rigol DSA815, which is of course nice in that it has a USB port and can save screen shots and other settings to a USB stick, color screen, networking, and all of that bling.But truthfully, the older models can do the basic things you need from a spectrum analyzer just as well. I have an Agilent E4411B and an hp 8594E. They both do the things you always need - measure power, check for spurious emissions, markers, trace functions like Max Hold - all the things they were designed for in the Beginning.

author: tautech
author_rank: Super Contributor
timestamp: March 09, 2024, 02:28:56 am
content: Quote from: ballsystemlord on March 09, 2024, 01:46:50 amConsider a single device instead of 2.SSA3050X-R might meet your needs.Or for that matter, the bit cheaper SVA1075X and getting you to 7.5 GHz capability.

author: rsjsouza
author_rank: Super Contributor
timestamp: March 09, 2024, 03:07:58 am
content: Quote from: ballsystemlord on March 09, 2024, 01:46:50 amI will focus on the wireless device and not necessarily on the oscilloscope.Output power measurements can be done with the Spectrum Analyzer. If you intend to keep things at bay w.r.t spurious and harmonics, provide for something at least 3x your fundamental frequency. ISM bands can have many frequencies (13, 27, 433, 868, 915, etc.), so choose accordingly. Also, sensitivity and noise floor are important, especially if you intend to do irradiated measurements. Some field units have higher noise floor than lab ones, so be watchful for that.A VNA will not help you with output power, but it will help you perform matching and characterize baluns, filters, transmission lines, etc. if you have a 2 or more ports. A similar rule as above will be useful: 3x the desired bandwidth. Also, be sure to include in your budget a very good cal kit - a VNA is hopeless without one.Overall, you also have to budget good quality cables and adapters - especially for the VNA.As for the old versus new, I regularly use an old iron HP VNA from the early 1990s and a few more modern (turn of the century) Agilent units. On occasion I use very modern R&S units full of bells and whistles. The old HP runs absolutely fine and drives wonderfully, but it lacks the modern conveniences such as saving data to USB pendrives, or having mouse/keyboard control, for example. The data transfer is easy to be done via GPIB, so nothing blocking. The more modern VNAs from Agilent and R&S also have more internal memory - something important if you want to use more acquisition points at a wider bandwidth. The more modern Spectrum Analyzers can also be furnished with additional data and protocol processing, have multiple preconfigured modes for specific tests (CISPR, for example), but these are usually options.That is a very broad brush to this topic, but it should give you a start. Good luck in your research!

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: March 09, 2024, 02:52:15 pm
content: Are either of those options hackable? Like for options? Or if I got the lower end model, to increase BW?

author: baldurn
author_rank: Regular Contributor
timestamp: March 09, 2024, 03:26:24 pm
content: Quote from: ballsystemlord on March 09, 2024, 02:52:15 pmThe Siglent SSA3032X-R 3.2GHz can be upgraded to Siglent SSA3075X-R 7.5GHz with all options enabled. There is a thread here about how to do that.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 09, 2024, 07:19:56 pm
content: Quote from: ballsystemlord on March 09, 2024, 12:43:09 amI wonder what You have learned in your research. Also not sure what constitutes serious work.My early SAs were swept types with analog filters and were very slow. Eventually got one with digital filters. Back in 2016 I got a Signal Hound BB60C which is a low end RTSA.https://www.keysight.com/us/en/products/spectrum-analyzers-signal-analyzers/real-time-spectrum-analyzers.htmlhttps://www.eevblog.com/forum/testgear/signal-hound-bb60c/VNA wise, my first one was all manual. Grease pen on the screen with plastic overlays...https://www.eevblog.com/forum/projects/20db-rf-attenuator-seeking-feedback-to-improve/msg2903552/#msg2903552Current one is an old Agilent four receiver PNA. Feature wise, there are way too many to list and guessing from your own research you already know most of it. I did try to work a deal with PicoTech to have a look at their VNA. Spec wise, it was similar to the PNA.Make sure you understand what you need and read the manuals to make sure that what you buy fits your needs. Good luck.

author: nctnico
author_rank: Super Contributor
timestamp: March 09, 2024, 07:26:10 pm
content: My biggest issue with older equipment is that lack of a USB or ethernet port to save data / screen captures. My experience with floppy to USB converters has not been good either. Nowadays I use a Prologix GPIB to ethernet interface to interface to old equipment which works well in combination with some Python scripting.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 10, 2024, 12:29:12 am
content: Quote from: nctnico on March 09, 2024, 07:26:10 pmMy biggest issue with older equipment is getting it fully functional and then maintaining it. For higher end equipment, locating replacement parts that may have been custom can be costly and time consuming. My advice if you are buying used, consider making the calibration part of the agreement. Maybe have them ship the unit to the manufacture and if it passes cal, you cover all the cal and shipping costs.My old PNA and scopes support Ethernet which is how I control them. For older test equipment, I use an Ethernet - GPIB controller from National Instruments. For the USB floppy, I have one from eSYNiC. For printing, I designed a Centronics to Ethernet reverse print server (using a Motorola 6811).

author: xrunner
author_rank: Super Contributor
timestamp: March 10, 2024, 01:03:08 am
content: If I want a screenshot from the old hp 8594E I don't need no stinkin USB stick or floppy drive. I can brute force one ... using my phone camera.

author: nctnico
author_rank: Super Contributor
timestamp: March 10, 2024, 01:30:09 am
content: Where is comes to actual equipment recommendations:Many base station analysers have spectrum analysis and network analysis features. I got one from JDSU / Viavi which does both. These typically don't break the bank. The JD745B/JD785B models could be interesting but make sure to understand the available options versus what is installed on the units.

author: G0HZU
author_rank: Super Contributor
timestamp: March 10, 2024, 02:27:03 am
content: For many years, the industry standard spectrum analyser was the 22GHz HP 8566B or the very similar looking 1500MHz HP 8568B. These are still fabulous spectrum analysers today, but they are big, heavy and have a LOT of fan noise.They are also going to be fairly unreliable today. The log detection is done in the analogue domain so the log accuracy isn't that great, especially over an 80-90dB range. The RBW filters are all analogue. So it is very slow to sweep on narrow spans and the filter accuracy is going to be a bit dodgy by now unless it has been serviced fairly recently.They still easily outclass the modern Rigol and Siglent analysers in terms of spurious free dynamic range and phase noise but they lose out on pretty much everything else. The CRT displays are getting very tired now although the vector system they use is equivalent to a 1000 x 1000 display. So (in theory at least) this is better than the Rigol or Siglent. However, most people will much prefer the larger modern display of the Siglent, and I can see why. The Siglent analysers do have a great looking display. For most hobby users and some professionals, the Siglent SA is hard to beat.Few professionals will still be using an HP 8566B or HP 8568B. There are too many modern alternatives with modern features that these older analysers don't have.The other option is the HP 8560/8563 portable analyser. These have similar performance to the 8568 and 8566. At work these 8560/8563 portable analysers are dropping like flies. I think the company still had about 8 of them a couple of years ago and all of them have died in the last year or so. Nobody wants them, nobody wants to pay to have them repaired and they are all going (or have already gone) for WEEE recycling.The HP 859x series are very popular but the RF performance is grim. It was grim 30 years ago and in my opinion these analysers aren't worth having unless you are desperate and don't care how grim they are. The same applies the Tek 49x series of spectrum analysers.

author: G0HZU
author_rank: Super Contributor
timestamp: March 10, 2024, 02:39:56 am
content: In terms of VNAs, the old HP 8753x series offered really good performance. Easily better than the modern sub $2k Siglent VNAs and they also offer bias tees at the rear. The main niggle with them is the clunky and restrictive user interface. Newer VNAs from Agilent/Keysight that replaced the 8753x series are much more versatile when it comes to setting up the calibration of a test fixture for example and the newer VNAs support unknown thru calibration which can be very useful. They also support the popular Agilent Ecal modules.The popular VNAs from Siglent that are based on their budget spectrum analysers are going to be fairly grim in terms of performance. However, if you just want to do casual measurements of antennas or filters then they should be fine. The big old lab VNAs are still hard to beat if you want to make fairly precise measurements of n port networks up into the GHz region. No nanovna or budget Siglent VNA is going to come close in this respect.

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: March 10, 2024, 03:00:43 am
content: Quote from: rsjsouza on March 09, 2024, 03:07:58 amThe alluded to device would probably make me money more quickly and easily than the scope. But whenever I see electronic equipment, I start to think of how it could be better. You know the TEA thread? That's what I am but in reverse. I have fantasies about hand solding prototype high-end electronics. It doesn't matter if it's an oscilloscope or a calculator, I still want to make one and make it better. Maybe I should seek professional help. Hey, any EEs want to give me a hand? -- Well I did say professional, never mentioned psychiatrist.

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: March 10, 2024, 03:09:03 am
content: Several people so far have pointed out the lack of being able to take screen shots using USB as a bit of missing functionality. I'd like to point out that USB screen shots tend to be a tacked on feature and they don't even necessarily work. Please note that I'm not trying to rant against any of you. I'm pointing out that this really is not a big deal because of how borked it is, at least in my experience.For example, you have modern equipment that can only take one shot because it overwrites the previous image no matter what you do.And when the feature does work it's "tacked on". As in, unlike your camera, it will overwrite all it's previous screen shots or prompt you to overwrite them. Entering new file names is only available on some equipment and those it does work on require you to go through several menus to get there. It's a pain. It's far faster to rename all the screen shots on your PC after capturing them via USB thumb drive or camera.

author: tautech
author_rank: Super Contributor
timestamp: March 10, 2024, 07:10:08 am
content: Quote from: ballsystemlord on March 10, 2024, 03:09:03 amRant you are and lacking in experience shooting your mouth off this way.Image capture tools in modern equipment are more powerful than you could ever imagine and simple to use.These are from a SVA1032X that is out the door to a customer tomorrow but a few quick screenshots first and some explanation of how an analyzer works and what screenshots look like.CW is the setting we most use, Clear/Write in that the previous sweep is cleared as a new sweep is written.We can sometimes see the sweep marker on the trace as in the cw screenshot half a division before mid display.BTW, all these were named in seconds before saving to USB or Local using the front panel alphanumeric keypad.Should we want sweep stopped for a screenshot we use View to stop the sweep and take the picture or to preserve the sweep and activate an additional trace with different settings.Finally most modern equipment has internal storage for screenshots and all manner of required captures, be it a calibration file in the case of one of these VNA's or just for reference files of which we with the File Manager shift to USB, copy from USB, delete, copy/paste etc.The File Manager screenshot was first saved to Local memory then shifted to USB and brought here as an example of this functionality.BTW, all this functionality and more is even present in the cheapest analyzer from Siglent, SSA3015X Plus.Further reading of capabilities starts here, albeit with the the earlier SSA3000X series:https://www.eevblog.com/forum/testgear/siglent-ssa3000x-spectrum-analyzers/msg958295/#msg958295

author: baldurn
author_rank: Regular Contributor
timestamp: March 10, 2024, 01:24:11 pm
content: It is an interesting topic. I don't know too much about the old hardware but I researched some of the options given by G0HZU. I know my Siglent SSA3032X-R (all features unlocked and unlocked bandwidth of 7.5 GHz). Given the purpose of testing some wireless device at 2.4 GHz this is what I suspect is useful and not present in the old HPs:Modulation analysis for digital modulations. AM/FM, ASK/FSK/PSK/MSK/QAM. How are you going to know if your modulation is any good with the old device?Real Time Analysis Mode. The Siglent can do 40 MHz of real time bandwidth. Needed to be sure to capture short bursts of data transmission.Network connected. The talk about screenshots - we do these from our PC connected by ethernet (usb is supported also but I never do it that way). None of the problems you mention are actually a problem with this modern device.Working with a modern UI that has touch screen and option for using a mouse.It is probably faster (scan time etc) but I don't know for sure.It has 1 Hz RBW (the HP has 10 Hz) but other than that, I don't necessarily think you should be comparing specs. Is the VNA not as good as the old HP? I don't know but it gets the job done just fine. Unless you have a special need that is depending on these specs, it should be more about which instrument have the needed features.Cheaper? Maybe but anyway the Siglent is within the stated budget and is a single device with both SA and VNA. But you need to hack it or pay a lot more.

author: zrq
author_rank: Frequent Contributor
timestamp: March 10, 2024, 02:17:55 pm
content: Quote from: nctnico on March 10, 2024, 01:30:09 amI also got a JD785A, which one can get on eBay for ~$2k with the SOL cal kit. It do have okay RF performance on datasheet, in particular for SA dynamic range (2/3 (TOI-DANL) in 1 Hz RBW: >104 dB) and phase noise (typ. –112 dBc/Hz at 1G, 100k offset), and it's modern, portable and hackable. Data saving, remote control and transferring is a piece of cake as there is LAN and USB, and one can be creative as there is a modern linux system running on armv7 inside serving SSH, HTTP and FTP.Also 7x5A and 7x5B seems to be identical except the useless RFoCPRI function, unless you want to play with RRUs.However, one should understand their limitations before getting one (or E7495A/B or other Agilent handhelds that are not FieldFox), not only the limitations visible on the datasheet like the dynamic range of the VNA mode is only 80 dB (which isnot betterthan the budget Siglent 3.2 GHz VNA, the higher frequency Siglent is 20 dB better IIRC), and also hidden caveats like1. AM/FM demodulation is not continuous but only limited to a certain record length.2. Marker readout is too slow to use.3. The CW generator is noisy and have poor harmonic rejection.4. Somehow the video triggering for gated sweep doesn't seem to work, it always stays in free running.5. Bugs exist like recalling VNA settings with calibration can led to garbled reading. (the latest and likely the last firmware revision)6. The VNA does not measure phase and magnitude simultaneously (at least I couldn't get it to), but need two measurements to get the complex data.7. Forget about using the cellular analysis functions to look at generic complex modulated signals, it will likely require a significant amount of hacking.8. The VNA only uses a very very basic calibration model, assuming the cal kit is ideal.If I had 2x of the available budget, I should have got myself Siglent SSA3032X-R instead of this. But hey, for only $2k one can get a bundle of a 8G SA and 6G VNA, they should work for your transceiver development despite their limitations. The handheld form factor make it not only ideal for field work, and also in the lab much less head scratching moments realizing the cable is not long enough.

author: G0HZU
author_rank: Super Contributor
timestamp: March 10, 2024, 03:33:41 pm
content: Quote from: baldurn on March 10, 2024, 01:24:11 pmYes, the real time Siglent SAs are really powerful. The older HP analysers can't do real time analysis so there's no contest here at all in this respect.It will also be very difficult to measure the output power of a modulated WiFi transmitter with one of these old HP analysers!The HP 8566 analyser ought to be better on traditional things like (typical) frequency response accuracy up to 2.5GHz, input VSWR with 10dB attenuation, carrier phase noise out to 1MHz offset, input IP3 vs MDS, internal spurious levels and blocking dynamic range at (say) 100kHz or 1MHz offset.The 8566B might also win on sweep refresh rate on large spans (eg >2GHz).

author: trackersoft
author_rank: Contributor
timestamp: March 10, 2024, 06:00:12 pm
content: Interesting topic. I have a bench full of nice but older Tek and HP gear and my HP 8591E with track gen is looking kind of old compared to the Siglent SSA3015X Plus and my older eyes would really like the bigger color screen! I am a ham and restore Collins military, ham and commercial gear but I have spent more time repairing test equipment in the last year than working on radios. I think I will spend the next year replacing some of the older gear with Siglent. I still refuse to get rid of my 2 141T's just for nostalgia sake though.

author: G0HZU
author_rank: Super Contributor
timestamp: March 15, 2024, 07:19:13 pm
content: QuoteThe HP 8753x series are usually configured as full 2 port VNAs that can do 12 term correction. The Siglent SA/VNA looks like a basic T/R VNA. Therefore, I'd expect the port match of the Siglent VNA to be quite poor and I'd expect the directivity to be relatively poor.So in this respect there isn't even a contest. The HP is a different class of VNA because it is a full 2 port VNA. The Siglent SA/VNA doesn't qualify for the contest because it's just a T/R VNA.

author: tautech
author_rank: Super Contributor
timestamp: March 15, 2024, 07:36:11 pm
content: Quote from: G0HZU on March 15, 2024, 07:19:13 pmNot all.Check out the SNA5000A range and SSM5000A Switch Matrix which can provide 24 ports.

author: baldurn
author_rank: Regular Contributor
timestamp: March 15, 2024, 07:49:15 pm
content: Quote from: G0HZU on March 15, 2024, 07:19:13 pmThe Siglent SSA3000X-R can do S11 and S21 measurement using two ports. It will not do S22 or S12 as only the one port can transmit. You will therefore have to switch the ports manually to get those done.

author: G0HZU
author_rank: Super Contributor
timestamp: March 15, 2024, 08:23:50 pm
content: Quote from: baldurn on March 15, 2024, 07:49:15 pmIn other words, the Siglent SSA3000X-R is just a T/R VNA. So it doesn't qualify as a full 2 port VNA.

author: TimFox
author_rank: Super Contributor
timestamp: March 15, 2024, 08:33:18 pm
content: Two useful reference books about the previous generation of swept-spectrum SAs with digital control and analog processing (ca. 1990) with examples from Tektronix.(1) M EngelsonModern Spectrum Analyzer MeasurementsJMS, 1991; Practical uses.(2) M EngelsonModern Spectrum Analyzer Theory and ApplicationsArtech House, 1984; More mathematical background than (1).

author: baldurn
author_rank: Regular Contributor
timestamp: March 16, 2024, 01:22:38 am
content: Quote from: G0HZU on March 15, 2024, 08:23:50 pmThe OP said he needed it to build an antenna. Besides you can do most things by switching the cables. It is just not as convenient. You can get all four S parameters.I am not sure the claim that it will do worse measurements just because of only having one transmit port can be correct. But I have read that spectrum analyzers are build as SA first and the VNA part is tacked on trying to reuse circuits made for SA and therefore typically has worse performance. Unless OP can specify some requirements, I am going to assume the performance is more than good enough for what was described.Siglent does have a device for 2 and 4 ports VNA with all ports equal. It is the SNA5000A but it is over budget even for the cheapest option. This does include a SA option and in this case it is the opposite of the SSA3000X-R: The SNA5000A is VNA first and SA second. Does seem to lack the protocol decodes and the RT option, which they are selling, does seem to be missing in the manual.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 16, 2024, 02:36:30 am
content: Quote from: baldurn on March 16, 2024, 01:22:38 amMissing the more advanced error corrections.

author: G0HZU
author_rank: Super Contributor
timestamp: March 16, 2024, 09:24:43 pm
content: QuoteHave a look through this dochttps://www.kirkbymicrowave.co.uk/Support/Links/application-notes/HP-Agilent-Keysight/Keysight-Applying-Error-Correction-to-Network-Analyzer-Measurements_5965-7709E.pdfThe first couple of pages show how much better a full two port calibration is. See figure 1 that shows a full two port cal vs the response cal. The response cal has a lot of ripple on it. However, the ripple can sometimes be a lot worse than this.It is possible to use external attenuators on the ports to improve a T/R VNA when measuring S21 and S12, I did this for many years using an old HP 8714B T/R VNA. It is very clunky to do this, especially if trying for all four s-parameters. I did this for many years until I upgraded to a more capable VNA.

author: baldurn
author_rank: Regular Contributor
timestamp: March 16, 2024, 11:28:22 pm
content: Quote from: G0HZU on March 16, 2024, 09:24:43 pmBut the Siglent SSA3000X-R will be doing the full two port calibration named "Short-Open-Load-Through (SOLT)" above figure 1?Maybe we have a misunderstanding. It can only transmit on one port but it will receive on two ports. It will therefore do a two port through calibration just fine. Naturally in addition to the short, open and load calibration.

author: G0HZU
author_rank: Super Contributor
timestamp: March 17, 2024, 01:44:03 pm
content: Quote from: baldurn on March 16, 2024, 11:28:22 pmOK, I can try and explain my point. I think the Siglent SSA3000X-R is a T/R VNA and it can do something called an enhanced through calibration. This corrects for the port 1 mismatch but this isn't as good as a full 2 port calibration because it can't correct for the port 2 mismatch. Port 2 won't be a perfect 50R port. It will have some mismatch.By contrast a genuine full 2 port VNA can typically do a 12 term correction that includes correcting for port 2 mismatch.If it helps, the red trace in the plot below shows what a perfect VNA could measure (in terms of S21) for a fairly short 25 ohm transmission line between port 1 and port 2.The red trace is close to what a proper lab VNA would show if it supported a full 2 port calibration. This is the correct response.If the T/R VNA had an uncorrected port 2 VSWR of 1.3:1 (but everything else was perfectly calibrated correctly) then the best you can hope for is an uncertainty window represented by the blue trace.Can you see how grim the T/R VNA performance is in this comparison? It is possible to add an attenuator at port 2 of the T/R VNA to improve things but this comes with the penalty of reduced dynamic range.