Hi Sarma,
Thanks for your answer, any help is welcome, and I'm sure I will finally find out what's happening. It's also the fun of building your own rig, hey?
Please note, I am not using the Raduino, but a standard Nano and an Adafruit SI5351 board. Neither do I use a rotary encoder but the old 'analog' method of tuning, where the rigs start running up and down at the tuning pot's ends.
Currently I am 'walking around' with the oscilloscope probe to get a 'feeling' about the signal. It's clear that the ground copper clad around the audio amp is not clean from noise. I just need to find out why it does work with the old Nano. The supply and ground leads around the Nano and SI5351 boards are clean. The tuning pot leads are clean also. I can reduce the clicks slighty by connecting a heavy screwdriver from the metal cabinet to ground close to the audio amp.
Better grounding will help, but it's strange that with the old Nano it works without any noise. I can't imagine that the broken IO port actually helps in this case.
I'm confused as to what you mean with the CH340 USB chip with FT8. USB is not connected during the tests. Firmware is uploaded to both Nano's and then USB is disconnected
73, Alex
