Thank you for your replies.
I will check the frequencies of the Arduino and BFO with another transceiver.
I have tried to move cables around but this had no influence on the tones.
Please note that the strongest tone is at 5,426Hz and with more up to 15KHz. So if I go the audio filter way it will have to be pretty steep I suspect.
In desperation I have thought of cutting the traces of the BFO line and one of the two other oscillators and wire swap them around, then changing the sketch accordingly. Would this prove/disprove a coupling issue?
I could buy another Raduino, my only issue is then what if this is on the main board?
So if the frequency test does not show anything out of the ordinary I will buy a header-less Arduino Nano and attempt the swap.
How do you de-solder the arduino? Is a de-soldering braid effective?
To Bill: I used "Spectrum Analyzer"? from Rasberrywood (the free version seems fine for radio audio analysis).
All the best,
73, John (VK2ETA)
