Hello to all. Thank you for the many suggestions and combined experience.
I just completed a lengthy post, which accidentally started a new topic (title line got corrupted). Therefore, I deleted it, and reproduced it here.
It looks like my problem is mostly resolved. There are still some minor adjustments to make.
Evan, Your diagrams are similar to what I have ended up with. The attached diagram was drawn from two separate plots on the Antuino. I was expecting the Clock #0 signal to be much narrower than shown, and that it would be positioned near the upper end of the crystal filter passband. (A few posts mentioned better test equipment. I used what I have. But I will look into the alternatives suggested.)
My observation is that the HF signals online BFO calibration tool is helpful, but not precise. It is subject to the user's perception of where the noise pedestals should be placed. The background noise in various regions and environments vary substantially. I was not able to get a well pronounced noise pedestal at the low end of the spectrum. Now, that things seem to be corrected, the noise spectrum still does not match Ashhar's demo.
With the help of all of you who shared insights and experience, and with a few tidbits found elsewhere on the forum, here is what I did:
1. Perform BFO calibration according to Ashhar's demo (antenna connected, receiver tuned to noise not signal). This enables the receiver to pass a signal. But although I had done this procedure several times, the receiver was not differentiating LSB and USB. Also, the transmitter, in SSB mode, had 3 watts RF output in the absence of audio modulation.
2. Adjust BFO calibration while listening to SSB signals (antenna connected, receiver tuned to SSB signal,.with the receiver in the BFO calibration mode). Adjust the BFO settings for the best USB audio. Do the same with an LSB signal. (If using KD8CEC firmware, ensure "IF Shift" is Off.)
3. Calibrate the receiver frequency, for zero-beat on a known signal. My preference is WWV, but multiple signal paths (do to long propagation distance) often cause difficulty with finding zero-beat. A strong HF broadcast station, without much fade, may work better.
4. Recheck BFO calibration (step 2.).
5. Adjust CW BFO (not on all systems, but included in KD8CEC firmware). I have not done this yet. But I think it involves listening to a good CW signal, and adjusting for best clarity (as done for SSB in step 2.)
6. Verify sidebands are correct (not reversed). Other posts recommend tuning to 7074 Khz, in USB mode. If propagation allows (better in evening), you should hear FT8 signals in USB mode (but not in LSB mode). Also verify CWL and CWU are correct (FT8 audible in CWU mode only).
7. Verify correct transmit operation. Disconnect microphone. Transmit into a dummy load, monitor RF power output. Key the transmitter from the mic jack, not from the keyer jack. There should be no RF output in the absence of audio input. Repeat test in both USB and LSB.
(If steps 6 or 7 are incorrect, further BFO adjustment is required.)
It looks like things are about where they should be, now.
Thank you all.
