[K3] RX audio distorted on FM

[Pete-Astound]

Good evening All,

Well I've had a chance to play around some more and now
found that at least with a local signal from the 817 the
audio distortion on FM receive seems to have mysteriously
disappeared.

One question I still have though is that with an antenna
hooked up and listening on either 10 or 6 meters when the
band is quiet (night time with the pre-amp and attenuator
off), does the background static get at least twice as loud
if not more when you go from any of the modes to FM?  Seems
like it did not does this when I had just the 2.7 filter
installed into slot 3.  Tried turning the slot 1 filter off,
but it still defaults to it when in FM mode so I can't
compare unless I go back in and physically take that filter out.

Thanks for your responses..

Pete - WD6DKW
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[N5GE]

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


On Thu, 24 Nov 2011 22:50:37 -0800, Pete-Astound <[hidden email]> wrote:


>One question I still have though is that with an antenna
>hooked up and listening on either 10 or 6 meters when the
>band is quiet (night time with the pre-amp and attenuator
>off), does the background static get at least twice as loud
>if not more when you go from any of the modes to FM?
[snip]

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[John Lemay]

Pete

I confirm it's normal and common with most rigs. But if you don't like the
background noise on FM you can use the "squelch" control to cut it out.
Careful setting of the squelch will ensure no background noise but as soon
as a weak station is received it will "break the squelch" and you will hear
it.

John G4ZTR

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of [hidden email]
Sent: 25 November 2011 08:13
To: [hidden email]
Subject: Re: [Elecraft] [K3] RX audio distorted on FM


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


On Thu, 24 Nov 2011 22:50:37 -0800, Pete-Astound <[hidden email]>
wrote:


>One question I still have though is that with an antenna
>hooked up and listening on either 10 or 6 meters when the
>band is quiet (night time with the pre-amp and attenuator
>off), does the background static get at least twice as loud
>if not more when you go from any of the modes to FM?
[snip]

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[Pete-Astound]

Morning All,

Sounds good and makes total sense..

Thank you for the responses..

Pete - WD6DKW
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[Raymond 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, [hidden email] 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
>

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[Bob Cunnings NW8L]

Actually, no, not for FM. Just as you say, most FM receiver IF
circuits run the circuit gain at maximum. Also, a conventional FM
receiver IF contains one or more limiter stages. Quieting is not a
function of reduced IF gain - it is  a function of the limiter.
Quieting is observed as signal strength rises past the point where
limiting begins, and full quieting occurs at the point at which the
signal is strong enough to saturate the limiter so that no AM
component remains.

Bob NW8L


>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.
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[Raymond Sills]

HI Bob:

Yeah... that's what I meant!  :)   There is that point where there is  
no further signal gain is possible.. i.e. hard limiting.  So, you are  
quite correct.

Thanks!

73 de Ray
K2ULR
On Nov 25, 2011, at 12:18 PM, Bob Cunnings wrote:

> Actually, no, not for FM. Just as you say, most FM receiver IF
> circuits run the circuit gain at maximum. Also, a conventional FM
> receiver IF contains one or more limiter stages. Quieting is not a
> function of reduced IF gain - it is  a function of the limiter.
> Quieting is observed as signal strength rises past the point where
> limiting begins, and full quieting occurs at the point at which the
> signal is strong enough to saturate the limiter so that no AM
> component remains.
>
> Bob NW8L
>
>
>> 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.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
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