This might be slightly off-topic, because the interference generation
problem I need to solve involves long wave radio - please suggest a
better group to post to if you know one.

Problem: Located in the UK, I have a robot mower which is guided by a
perimeter wire laid around the edge of the lawn. Works fine, but
generates RF interference which hits my neighbour's long wave radio
reception (e.g. station Europe 1 at 183 kHz).

First attempt to solve: I have put a filter provided by the mower
manufacturer in-line with the drive to the perimeter wire loop. This
makes a difference - instead of all stations being wiped-out, you can
now hear them, but listening to some stations is unpleasant because of
interference whistles which are still present at various frequencies.

Next attempt to solve: The mower manufacturer is about to send me a
second similar filter, which I can try instead of or in-line with the
current filter.

In case that does not work well enough, can anyone suggest a DIY
filter that should fix the problem?

Thanks,
John