Just a thought - maybe it's your generator/alternator/voltage regulator rather
than the mags. After engine start, turn off the charging system if you have a
split master (or pull the fuse/breaker if you don't). If the problem goes away,
it's in the charging system. Your old radio may just not have been as sensitive
to electrical noise. Doesn't mean the new one is defective.

Best regards,

Steve Robertson
N4732J 1967 Beechcraft A23-24 Musketeer

Eugene Wendland wrote:

I just installed a Michel TKM MX 11r which is a direct slide-in replacement
for my Narco 120 Comm. Because I have an intercom, I had to add a resistor
to the circuit board. Having done this, I installed the radio in the old
Narco tray and tested the radio:

Findings:

1/ Comm works great with just power on.
2/ With engine (lycoming O-320 with new mag leads) on at low r.p.m.s, the
received audio has interference (very garbled).
3/ Once the r.p.m's increase to about 1500 and beyond, the recieved
transmissions seem great.

Because TKM is closed, I haven't called the tech rep about this, but could
anyone tell me what's happening? Everything else about the Comm seems to be
working well. My transmissions to the tower are 5 squared. My Narco didn't
do this, so I'm assuming there's something wrong with the radio.

Thanks

Eugene Wendland