w9ran
commented
3 days ago Jon, please ignore my comment about AM mode, I momentarily forgot there will be no phase/frequency modulation only amplitude. Instead let me focus on LSB mode, where I happened to capture the anomaly within 1 minute after start-up in this video: https://share.icloud.com/photos/0acC_j49Yn53qOiVZF0-Xr7PA
You can see the broadband noise and hear it in the receiver, with a silent period when the audio loops. After 16 seconds, you hear one cycle with correct LSB modulation, then it returns back to noise. About 2 minutes after making this recording correct modulation appeared and continued without interruption. The receiver and spectrum analyzer are loosely coupled to the gate drive signal, which is the OSC signal from GP8 of the Pico, buffered through two 74AC00 gates wired as inverters to drive the MOSFET PA gates.
I'm seeing inconsistent operation of the transmitter in which no audio is present, even though the RF drive is present. I confirmed this by looking at the RF signal at the gate of the MOSFET in AM mode, which shows a steady carrier but no audio. In SSB, broadband noise appears and can be heard to diminish at the end of the audio file and resume when it loops. Stopping and restarting, power cycling, etc does not restore correct operation.
Occasionally the audio will begin as it should, but I haven't been able to identify what triggers proper operation. I suspect it that no or incorrect serial data is being sent via USB when this happens even though the transmit.py program runs OK. When streaming does start correctly it sometimes will run reliably for an hour or more, although at times it stops intermittently with a time-out message for reasons unknown. Transmit.py is running on a Windows 10 PC. Bob