Products > Test Equipment
HP3577A 5Hz-200Mhz VNA Teardown
precaud:
--- Quote from: rx8pilot on July 29, 2018, 01:20:18 am ---The error message only flashes on the CRT for a second, but only when you power it up. That means the CRT is not yet displaying anything. I only noticed the message when I pressed the reset button on the processor PCB with re-boots without turning the CRT off. It allowed me to see the startup sequence. Led me right to the end of the rainbow.....
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Nice!
--- Quote ---It looks like these can deal with 25VDC on all inputs - not quite as delicate as the HF VNA's and SA's.
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Well I won't put DC on the inputs of mine... all three of my fixer-uppers have input stages issues, and DC is often the culprit... besides, DC shortens the useful life of relay contacts...
--- Quote ---That is my first attempt - an isolation transformer for testing control loop response. I am not sure how to set it up, normalize it and just get a scaler measurement of frequency response (as a first test). What is the proper setup to measure the frequency response of an isolation transformer?
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(Forgive if I make terminology errors, I mostly use an Anritsu VNA which uses different names for these things.)
If you want transmission response in a 50 Ohms system, or use the "Shunt-Thru" impedance technique, you need a splitter to isolate the R input from the load of the DUT. (Oh yeah, another thing you'll want to pick up at some point is a resistive splitter good to 200MHz...) An example of this is shown on p. 2-6 of the 3577A op manual.
But most often you'll want to measure transfer response from a 50 Ohm source, to include the loading effects of the DUT on the source, and into a load that you define. In the default menu, select A/R. Set inputs R and A to 1MOhm. Y the output to input R and xfmr primary. Solder a 50 or 100 Ohm variable resistor across one end of a BNC tee. That makes it easy to remove the tee to measure the R load its presenting. Maybe make some marks on the pot for certain R values. Connect the xfmr secondary to the tee, and into input A. In this setup, R=reference or stimulus, A=response. Set levels, freq range, display format, etc. Then make the sweep.
What some VNAs call "Thru", the 3577A calls "Normalize" and the Anritsu calls "X-S". At least the first two names make some sense :) The basic idea is to measure the inter-channel response difference at each freq so it can be subtracted from each subsequent measurement to remove the errors. Remove DUT and connect Output to both inputs (in this situation, set at 1MOhm) and make the sweep. Then turn normalize on and voila, future sweeps will be accurate. Any change of setup requires a new Normalize sweep.
Transfer function is the same as FRA (freq resp analysis), so if you've done any of that, the same rules apply at these low freqs.
There's another clever use of the "normalize" function. Since it stores a baseline measurement, you can use it as a reference of any sort to be subtracted from other measurements. Very handy if, for instance, you want to see how mag resp and phase changes as you vary the secondary load R on a xfmr. Make the "Normalize" measurement with DUT in place at some reference R load value (say, the value of the resistor you'll be inserting in a control loop). Then make sweeps with it set at some small incremental Ohms above and below the reference value, to see how the xfmr response changes as load R varies. With Normalize engaged, it shows you the deviation from the reference, so a flat line = no change. This makes differences much easier to see than comparing overlayed curves. This will quickly show you the useable freq range of the xfmr in those conditions; the range where the mag/phase resp of the xfmr doesn't change over the load range it will encounter.
This becomes really critical when you use a xfmr at lower impedances. Unless they were specifically designed for it, the HF bandwidth of most xfmrs really narrows at lower load R's.
--- Quote ---I tried a few setups, but they are clearly not correct. The OUT connected to the transformer with the INPUT A in parallel - I normalized that and it is flat. Then I move the INPUT A over to the output of the transformer - but the response looks nothing like what I would expect. I did the same setup on my scope with a signal gen and it is showing that -3db should be 10hz - 6Mhz.
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The analyzer wasn't set up to measure A/R. And the scope isn't showing you the attenuation of the input signal by the xfmr input impedance at that secondary load R. Set it up as described earlier and try it.
Hope this helps.
sixtimesseven:
--- Quote from: Jay_Diddy_B on July 29, 2018, 02:13:21 am ---
--- Quote from: sixtimesseven on July 27, 2018, 10:03:14 pm ---Yesterday the postman delivered another boat anchor to my doorstep - A HP3577A VNA with (75Ohm |O S-Parameter Test Kit).
Snip ...
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Be careful with the 75 \$\Omega\$ N connectors on the S-parameter test set. They will be wrecked if you mate them with 50 \$\Omega\$ N connectors. The center pin is a smaller diameter on the 75 \$\Omega\$ version.
I have both the 35677A 50 \$\Omega\$ and the 35677B 75 \$\Omega\$ test sets.
At lot of the time I use the 3577A for measuring Bode Plots on SMPS without a test set.
Regards,
Jay_Diddy_B
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Oh I did not know that :o Thank you I would have destroyed that connector. Now I have to order new adapters :palm:
sixtimesseven:
--- Quote from: precaud on July 28, 2018, 06:57:55 pm ---
--- Quote from: sixtimesseven on July 28, 2018, 06:37:09 pm ---I probably just install a quiet 12V PC fan with a 24V converter and test with the thermal cam if the 80 CFM are enough without the CRT heating the instrument.
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I look forward to seeing your results. Since you've been inside the unit, I think you can feel that most of the heat comes off the various PCBs, and it takes some pressure to get air to circulate among them all. I'm doubting if a standard PC fan will be sufficient.
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Well I have to agree with that. I interpreted the pressure to be in mm not in inches. 0.28in of H2O is a lot ???
Looking at Delta AFB 120 x 120 x 38 MM SERIES fans (https://www.mouser.ch/datasheet/2/632/AFB120x120x38mm-515857.pdf) the obvious replacement would be the: AFB1224HE. But I probably try the AFB1224ME which has a bit lower pressure (0.25inch) and CFM (~92) but then the noise drop of 12dB to 38dB is worth the risk to me.
precaud:
--- Quote from: sixtimesseven on July 29, 2018, 10:38:53 am ---Looking at Delta AFB 120 x 120 x 38 MM SERIES fans (https://www.mouser.ch/datasheet/2/632/AFB120x120x38mm-515857.pdf) the obvious replacement would be the: AFB1224HE. But I probably try the AFB1224ME which has a bit lower pressure (0.25inch) and CFM (~92) but then the noise drop of 12dB to 38dB is worth the risk to me.
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Well if it works, 12dB reduction is huge and would be well worth the effort! Keep us informed, please.
Berni:
I am just in the process of repairing one of those exact CRT modules in my HP 4145B since the NewScope5 is a bit pricy
It uses the same switches on the front panel and mine also have an inconsistent feeling. Some are soft and some are clicky. I am guessing that all of them ware supposed to be clicky but the springs got bent enough with use that they don't provide the buckling action anymore. But i prefer the soft feel of the worn out ones. I was guessing if jabbing the spring with a Flathead screwdriver would bend it enough to "break" the clicky action of the switch.
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