Tom Rauch w8ji at contesting.com
Mon Feb 19 12:59:19 EST 2007

> We have not been able to verify that particular problem, 
> so my question
> is whether powerline interference would cause such a 
> problem?  Most of
> the time powerline noise is amplitude modulated and thus 
> affects AM
> signals more.  So, what would the typical effect be on FM?

The radio doesn't know or care if it is FM, AM, SSB, or CW. 
When the noise is strong enough we will hear it.

FM can "capture" with a strong enough signal and a low level 
noise or low interference level......and AM is much better 
at detecting noise and converting to audio .....but nothing 
is immune to the noise wiping out the signal.

I recall FM being about 4-5 times better than AM for 
interference sensitivity for the same bandwidth, but in all 
cases the interference is weaker than the desired signal. 
Once it starts to approach the level of the signal even 
being FM does not help. In other words if a signal -20dB 
bothers you on AM, it takes a signal -13 or -14dB to be 
bothersome on FM.

I may be off a bit since that is a recollection from 30 
years or more ago, but I'm positive the general trend is 

73 Tom 

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