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| HP 8566B - What to look for? |
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| KE5FX:
Messing with the YTX is probably not going to be productive in this case. It could be damaged by DC, sure, but the damage would take the form of burning out the input coupling loop rather than the diodes. Application of enough power to damage the YTX is likely to damage the attenuator as well, which it sounds like you've ruled out. Refer to figure 1 in the August 1979 HPJ issue and you will see what I mean. (As with many HP instruments, HPJ actually provides a better technical introduction than anything in the official manuals.) If you were to replace the YTX you would have to recalibrate all of the the trimpots that define its tuning-current curve. You really don't want to go there if you can help it. Instead, try applying a CW signal at a few GHz and tracing the resulting 321.4 MHz IF through the Figure 2 block diagram in the HPJ issue, using (e.g.) your Anritsu. If you can't find the IF signal at all, check the current through the YTX tuning coil to make sure it's not open, and that its driver circuit is functioning at all. |
| W4PJB:
Thank you. I've been working on this during my spare time in the evening, so I haven't had much time to really dive into the block diagrams yet. I have a lot more time to do research over the weekend. Also, I always think of the archival value of these posts. Hopefully at some time in the future, someone may find the information here helpful, just as I have learned from past posts on this forum and on others! |
| G0HZU:
Good to see you got the display working again! If you get a bit of free time, could you do a quick screenshot of the phase noise at 100MHz on a 100 kHz span as in the image below? The image below is taken from the manual and it shows the front panel 100MHz (-10dBm) calibrator test signal being measured on a 100kHz span with the RBW set to 1kHz. Could you quickly show me what your analyser looks like with this test setup please? I'm interested to see how much cleaner the later models are in terms of phase noise. I checked the serial number of mine and it was made in 1982 so it would have been a fairly late A version converted to a B with the factory upgrade. My analyser looks very similar to the plot below. I'm interested to know if the loop bandwidth was changed at this span setting on the later models. It seems to be very narrow in the image below? On narrower spans the loop bandwidth appears to be wider on my analyser. I think my analyser has 1989 firmware as it flashes up 1989 when booting but the actual hardware appears to have been made in 1982. I'm not sure what the latest version of firmware is for these analysers. |
| W4PJB:
Ah ha! Progress is being made! I set the 8566B to 3 GHz, 10 kHz span, and low and behold, a little 4 dB blip showed up right at 3 GHz. (Sweep rate is slow so I have time to hit "Peak Search" and grab a photo before the next sweep.) Also, I connected my Anritsu to the 1ST LO out, and as to be expected, 3.321 400 GHz. So the great news is, everything is working! At least somewhat, enough to know the main components of the RF section aren't dead. It just has a very, very weak signal that disappears in the noise floor unless it's set to a very narrow span. I checked the attenuator and as expected, it's working fine. So, once again, on to the next thing! |
| W4PJB:
--- Quote from: G0HZU on June 21, 2024, 10:05:38 pm ---Good to see you got the display working again! If you get a bit of free time, could you do a quick screenshot of the phase noise at 100MHz on a 100 kHz span as in the image below? The image below is taken from the manual and it shows the front panel 100MHz (-10dBm) calibrator test signal being measured on a 100kHz span with the RBW set to 1kHz. Could you quickly show me what your analyser looks like with this test setup please? I'm interested to see how much cleaner the later models are in terms of phase noise. I checked the serial number of mine and it was made in 1982 so it would have been a fairly late A version converted to a B with the factory upgrade. My analyser looks very similar to the plot below. I'm interested to know if the loop bandwidth was changed at this span setting on the later models. It seems to be very narrow in the image below? On narrower spans the loop bandwidth appears to be wider on my analyser. I think my analyser has 1989 firmware as it flashes up 1989 when booting but the actual hardware appears to have been made in 1982. I'm not sure what the latest version of firmware is for these analysers. --- End quote --- My pleasure! Is this what you are looking for? Or did I miss a step? |
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