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HP 8566B - What to look for?
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G0HZU:
Thanks! That looks very similar to the plot from KE5FX.

Mine is probably about 1-2dB noisier than the (noisy) image I posted up from the user manual. It used to be exactly the same as the image in the manual, but I think my analyser needs a service. The phase noise has become a bit fluttery at times and I think I will have some more capacitors to replace. It has been quite reliable for the 14 years I've owned it, and it was in regular use for the first 8 or 9 years.

When you get the VNA set up, I think it's worth trying the input s11 test at 2.7GHz. You have to set the analyser to a narrow span at 2.7GHz to keep the YIG preselector in one spot. I would suggest using a 1MHz span or maybe less. Also, make sure you select 0dB attenuation and turn the VNA source power at or below 10dBm.
W4PJB:
Glad that was helpful! I would imagine the 8566 was on for about 10 minutes or so when I took that, so perhaps it would settle in a bit more after 30 minutes or so.

I tried the VNA (that has it's own thread, now  |O ) and was not able to get much resolution. Just as you suggested, I set the 8566 to 2.7 GHz, 1 MHz span (I even tried 100 kHz), 0 dBm, and set the VNA to -10 dBm, 2.7 GHz, and several different sweep widths. I calibrated the VNA on each change of span. Even at 100 MHz, there was no discernable notching in the reflection anywhere across the span.

KE5FX:
Try entering ATTEN 0 dB on the 8566.  You're probably looking at the YTX through the 10 dB attenuator (which is 20 dB once the VNA stimulus signal goes through it and comes back.)

They make you enter 0 dB explicitly to help protect the mixer from static damage.  Be very careful with ESD and signal levels while 0 dB ATTEN is in effect.
W4PJB:
Thanks, and great point about the signal being attenuated twice. I did set the 8566 to 0dB. VNA was -10 dB, as G0HZU suggested.

Guess it's not looking too good for Uncle YIG?
G0HZU:
Give me some time and I'll power up my 8566B and an old 8714B VNA. Both are in storage (under the staircase!) but I can dig them out and power them up together. It's very late here in the UK so I won't be able to do this until tomorrow but I'll try and produce some images of the return loss you can expect to see if the YIG is tuning OK.

As KE5FX warns, be careful of ESD, especially if you start taking things apart and checking stuff with a meter or other test gear.

I think you should see a dip in s11 of at least 10dB at 2.7GHz and it should be about 20MHz wide. It might be a bit wider than this, but I think it will be no wider than 50MHz. You do have to select 0dB attenuation with the 8566B. With 0dB attenuation the return loss will probably only be 1-2dB outside the passband of the YIG and maybe 10dB to 15dB inside the ~20 MHz bandwidth of the YIG.

This assumes that all is well with the YIG/mixer of course.

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