Digital Voltmeter causing interference
I am restoring a Rent-a-set radio and am posting elsewhere on this site on my progress but this one had me going for a full 40 minutes.
I had reached the stage where LW was working but with a really loud whistle superimposed. Checking with a scope showed that the audio had a 2kHz tone superimposed on it.
I spent a full 40 minutes trying to track it down before I decided to leave it for another day. Fortunately I switched off my test gear before switching off the set.
When I switched of the DVM the tone went, totally.
Switch it back on, tone returned.
The DVM is an Aneng AN8002 true rms meter.
I also checked 3 other DVMs and none of them caused the slightest interference.
I won't be using the AN8002 around radios again thats for sure.
Peter
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