[rabbit73]

OK, thank you for the images.

So, it isn't just channel 40.

There must be something wrong with your equipment or you have a serious interference problem.

Your signals are strong because of the antenna and preamp gain, but something is reducing the SNR of your signals.

Since it is intermittent, it will be difficult to diagnose.

The only thing I can think of now is to substitute each and EVERY part of your system with a known good part, even if it means ending up with a completely separate test system.

To check for interference, listen for noise on a battery operated portable radio that tunes the AM broadcast band.