Telamon wrote:
...
The OP already tried a isolation transformer so I don't think an
opto-isolator will be any more helpful.

I expect that it is a common mode noise issue. He can buy common mode
chokes that just clamp on the cables to find out.


Surely you jest, with optical isolation, there is NO direct connection ...

Unless you are proposing the rf is able to transverse the light beam.

JS