HP 8505A VNA - Page 1
Forum section: electronics / testgear

author: Squarewave
author_rank: Frequent Contributor
timestamp: January 06, 2021, 07:56:01 pm
content: I have suffered from the addiction of buying test equipment for some time.I'm now the owner of a HP 8505A VNA set, it has the 8501A normalizer and the 8503a S parameter test set. I just saw it at a bargain price and thought, I'll have a go at measuring coax and connectors with that, for no other reason than just having something looking nice to play with.It'll be something I'd like to learn about too, so I really ought to learn how to use it.Any tips on how to get to grips with this set and get going would be welcome. I have the manuals, but they appear to only be useful to someone who already knows how to use one. Sorry if this seems a bit vague

author: bob91343
author_rank: Super Contributor
timestamp: January 06, 2021, 08:13:27 pm
content: I am also fairly new to VNAs. I mostly use the Smith chart function although the others are very useful.You set the frequency range of interest and observe the impedance, SWR, and phase. The line length can be measured as well as characteristic impedance.A very useful device but I am not familiar with the model you have.

author: Bud
author_rank: Super Contributor
timestamp: January 06, 2021, 08:19:38 pm
content: For general VNA use Google for HP/Agilent VNA Application Notes.

author: eb4fbz
author_rank: Regular Contributor
timestamp: January 06, 2021, 10:55:53 pm
content: A VNA is useless without a calibration kit. Depending on the connector and frequency range you want to cover, you will find they are more pricey than the VNA itself.

author: xmo
author_rank: Regular Contributor
timestamp: January 07, 2021, 12:22:21 am
content: Start by tracking this down: 5952-9251 HP8505A RF Network Analyzer Basic MeasurementsAlso, there was a recent topic on the HP-Agilent-Keysight io group that discussed the 8505a and software for acquiring traces from the instrument.

author: xmo
author_rank: Regular Contributor
timestamp: January 07, 2021, 12:30:22 am
content: Don't run out and buy a calibration kit just yet.The 8505A calibrates using trace normalization.Full 12-term error correction came with the 8753A.See:http://hparchive.com/seminar_notes/HP_Introduction_to_the_Vector_Network_Analyser_-_HP8753A.pdf

author: joeqsmith
author_rank: Super Contributor
timestamp: January 07, 2021, 02:10:35 am
content: I have the 8754A which is an even older relic. Calibrating the 8505A shouldn't be that big of a problem. You have the 8501A. It has GPIB. You can use this to get the data into a PC. From there, it's up to you.I had someone contact me about porting my 8754A code to the 8505A. Wouldn't have been too much work. I offered to do it if they supplied me with a full, working 8505A which I thought was very reasonable price to charge back then. They declined. With all the open source code now available for the NanoVNA, you may want to consider using that as a starting point.Mine will work up to around 2.6GHz but my home made standards, which I still use today are really only good for about 1.5GHz before the are of little use. If you plan to work in the sub GHz, I see no problem rolling your own cables and standards.

author: Squarewave
author_rank: Frequent Contributor
timestamp: January 07, 2021, 05:08:12 am
content: Thanks for the replies so far. My max frequency will be around 450mhz, I can't see myself working any higher than that.

author: bob91343
author_rank: Super Contributor
timestamp: January 07, 2021, 05:34:00 am
content: The nanoVNA is the unit of choice as far as I am concerned. I sold off my boat anchor VNAs and now exclusively use the nano. I have a couple of spectrum analyzers as well so I am all set.The nano pretty much does everything the big units do, albeit at somewhat less accuracy and frequency range. My two nano units cover from 50 kHz to 1.5 GHz and for only $50 or less even came with decent calibration kits.

author: joeqsmith
author_rank: Super Contributor
timestamp: January 07, 2021, 02:45:57 pm
content: Funny, I recently added another boat anchor after playing with the original NanoVNA. The original NanoVNA, even that v2+4 I am playing with now, both make for very good learning tools. The low cost help make them an ideal combination for most hobbyist.I've never played with the OP's VNA but assume the test set includes a programmable step attenuator, transfer relay and bias T's. All expensive and all missing from the low cost units. I would also guess that the source has a much lower distortion and is level. With my 8754A, it uses a doubler to get above 1.3GHz. Not sure how the 8505 would be for narrow band work but the 8754A requires a separate RF generator to do it. The original Nano will far out perform it. But again, that HP was made in the 70's. Even with an external source, the dynamic range, noise..... it's just not a good tool. That's my biggest complaint with the V2+4, it can't be used for narrow band work but the solution is $50. Of course there are other benefits to the old boat anchors depending on their age.

author: Squarewave
author_rank: Frequent Contributor
timestamp: January 07, 2021, 09:31:06 pm
content: For reflection measurements I'll need to calibrate with a short. Is this a simple as using the type of connector I wish to use with the coax cable to be tested, but keeping one with a short from the centre pin to the body? Or is there more to a calibration short?

author: bob91343
author_rank: Super Contributor
timestamp: January 07, 2021, 11:58:26 pm
content: The calibration units aren't too simple. For instance, a short has a physical dimension and thus there is inductance. An open can radiate and has capacitance. These parameters are not critical at lower frequencies but when you start fooling with several hundred megahertz that's no longer true.If you are working below 500 MHz and don't need great accuracy, you don't have to worry about these things. Just don't get too casual, say by 'shorting' a connector with a jumper wire that is long compared to wavelength, say more than 5 - 10%. That would be an inch or three at 450 MHz. One wavelength is around 70 cm I think so anything more than a few cm will louse up your measurements.

author: Squarewave
author_rank: Frequent Contributor
timestamp: September 08, 2021, 04:53:08 pm
content: Just coming back to say that I've been getting to grips with this set. I've not been able to use a smiths chart for impedance measurements as I don't have the smiths chart overlays for this set, but otherwise transmission and reflection tests are ok.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 09, 2021, 12:00:41 pm
content: Print on overhead projector slides.

author: Squarewave
author_rank: Frequent Contributor
timestamp: September 10, 2021, 03:51:46 pm
content: I wouldn't have a clue what to do there, scales etc....

author: xwarp
author_rank: Frequent Contributor
timestamp: September 10, 2021, 09:20:21 pm
content: Quote from: Squarewave on September 10, 2021, 03:51:46 pmI use an 8505A, not in depth, but enough to enjoy using it for the LNA's I work on. You can use it without the normalizer. It has the smith overlay on it, which I don't use much. I'll see about pulling it off and scanning it if you'd like.

author: Squarewave
author_rank: Frequent Contributor
timestamp: September 12, 2021, 04:58:12 pm
content: I'm loving this VNA, just so big compared to what you can get nowadays, but it's still cracking for the little price that I paid.My connundrum at the moment is, for transmission loss measurements, calibration I need to connect through, so using a through connection to calibrate my test leads.There will be a small loss in the through connector, which is then 'calibrated out' which is then removed after! Is this a big enough issue?

author: xwarp
author_rank: Frequent Contributor
timestamp: September 14, 2021, 02:30:35 pm
content: Quote from: Squarewave on September 12, 2021, 04:58:12 pmIf it's figured into the calibration, then no.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 14, 2021, 04:28:43 pm
content: Don't you only have the normalizer? You can remove the offset but that's it?If your thru happens to be a 10dB attenuator and you normalize to that, guess what a good thru is going to measure.Use a good thru and cables and I doubt it will pose much of a concern.You have the same normalizer I have. It is possible to read the complex data from the normalizer with a PC and perform more complex calibrations and measurements. This is what I was doing. Softwares about 20 years old now.https://youtu.be/buG-H_LZH0U?t=400

author: Squarewave
author_rank: Frequent Contributor
timestamp: September 14, 2021, 08:25:55 pm
content: Quote from: xwarp on September 14, 2021, 02:30:35 pmWell, then yes.As it'll be removed for me to place my DUT in! So, those losses accounted for, are now a small amount of gain!

author: Squarewave
author_rank: Frequent Contributor
timestamp: September 14, 2021, 08:45:05 pm
content: Quote from: joeqsmith on September 14, 2021, 04:28:43 pmI don't think I have the means to PC control mine, without additional cables and software, probably not necessary for my purposes, but I get what you're saying.