[Elecraft] [K3] RX audio distorted on FM

[Ray Sills]

Hi Tom:

Very true.  And, another factor is that most FM receiver IF circuits  
run the circuit gain at maximum.  The resultant signal becomes  
distorted, but only in the sense that amplitude variations are  
totally removed.  No matter, of course, since you want to detect the - 
frequency- variations (it's FM, after all).  So, without using a  
squelch circuit to mute the audio, it's going to sound much louder.

In fact, most squelch circuits use that broad-band noise to determine  
that a signal is -not- on the frequency.  When a signal shows up, the  
receiver's AGC will detect that and turn the max gain down.  The  
difference in levels between the empty frequency and one with a user  
on it, "opens" the squelch, and then you hear the station.

When the incoming station is "full quieting"... it's signal is so  
strong that the IF gain is pushed down so much that the detected  
audio is "quiet".. i.e. no additional band noise.. just the clean  
audio to your speaker.  Same deal with FM broadcast receivers.

73 de Ray
K2ULR

On Nov 25, 2011, at 3:12 AM, n5ge at n5ge.com wrote:

>
> Yes, that is normal.  When you switch to FM you are listening to a  
> much wider
> portion of the band you are on.
>
> 73,
> Tom
> Amateur Radio Operator N5GE
> ARRL Lifetime Member
> QCWA Lifetime Member 35102
>