[Elecraft] Topband RF feedback problem

[Björn Mohr]

I had my first weekend with the new K3 and bumped into a strange problem. It
actually took me a while to figure out what was going on. When keying up
with the amplifier in line on 160 I was not able to run more than 400 watts
before the SWR protection in both the amp and SWR meter kicked in, it all
happened in milliseconds as if arcing was going on somewhere. I thought I
had an antenna problem and went through the system without finding anything
strange. After some time I hooked up my MP and all was fine again, running
full power without a problem. That’s when it hit me - RF feedback had to be
throwing my K3 off frequency and therefore tripping SWR protection and the
alarm. 

My setup has been working fine with the MP for over a year, never seen a
problem like this. A common mode choke is in line with the TX antenna and
most of the wiring used with the MP was used for the K3 except that power
where fetched from my 12 volt bus. The MP is a field model and gets its
power straight from the mains, same phase as the 12 volt bus. 

I would be interested to hear if anyone else had similar problems and found
a good solution. 

73 de Björn /SM0MDG