Aargh! Just found that on my BITX40, the torroid L4 was still in place - it should be removed when the raduino is connected to the DDS input.
So I removed it and now (most of) the AM carriers are gone. One problem less.
What is strange though, is that I am now receiving an extremely loud constant carrier on 7199 kHz. When the antenna is disconnected it remains equally strong so it must be internal to the BITX. I guess it comes from the raduino. Do any other raduino users have this issue?
73, Allard PE1NWL
Allard PE1NWL