Products > Test Equipment
HP 8566B - What to look for?
W4PJB:
--- Quote from: KE5FX on June 22, 2024, 10:50:15 pm ---Something else to note -- once you do observe an S11 response, you may get a deeper notch if you bump the 8753's point count up to 801. Depending on span, the default 201-point sweep may not have enough resolution to show the full effect. In fact, when making S11 or S21 measurements on a narrowband YTF using a wide VNA span, you can potentially conclude that a good filter is faulty because the notch lies entirely between two points. BTDT :(
Also: use 0 Hz span on the 8566. No reason to sweep the filter while you're trying to measure it!
--- End quote ---
I tried all of your settings, including the 801 point test, and still got basically no response. There was about a -4 dB drop at 2.7 GHz, compared to about -2 dB of other reflections. So the YIG is doing something, it's just not doing much. Or at least not much signal is getting into it.
KE5FX:
Post a photo of the 8566's screen?
W4PJB:
--- Quote from: KE5FX on June 22, 2024, 11:15:54 pm ---Post a photo of the 8566's screen?
--- End quote ---
W4PJB:
Hi All, just a quick bump on this post. I managed to secure a supposedly "tested good" YIG oscillator and tried swapping it today. Absolutely ZERO change in response. Still able to see a signal blip at around -94 dB on 2-22 GHz, still everything is in perfect operation on the low band. So unless this YIG is failed exactly the same way as the previous one, I'm going to say the issue lives elsewhere. I've got two more evenings to poke at this, then going on holiday for a bit.
BUT!!!! I did notice something else this evening. Perhaps this has been the case the whole time, and I just didn't notice until this evening as it's rather dim, but the red LED on the A6A7 YTX Current Driver is lit. I only noticed when I shadowed it momentarily so it wasn't getting washed out by the fluorescent light over my bench. This indicates the heater circuit is saturated and not reaching spec. Is this enough to cause my issue? :-// But it's a new breadcrumb.
As always, pictures attached.
KE5FX:
Maybe I missed it, but did you ever check the YTX tuning coil current?
If not, again, do that.
The heater circuit may or may not be OK but you don't usually lose 80+ dB when the heater goes south.
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