[RFI] VHF-AM radios

Maurizio Panicara Maurizio Panicara" <i4jmy@iol.it
Tue, 23 Jan 2001 23:25:17 +0100

The FM carrier must be placed on the IF filter slope (side) tuning the
signal more than a bit off the filter window.
To obtain a decent detection the IF filter shouldn't have a good shape
factor (LC is best) as much that with maximum deviation the attenuation is
not too big or the signal drops in the flat part of the filter.
In any case the distortion is well noticeable and increases with deviation.

Mauri I4JMY

----- Original Message -----
From: <dgsvetan@collins.rockwell.com>
To: "EDWARDS, EDDIE J" <eedwards@oppd.com>; <rfi@contesting.com>
Sent: Tuesday, January 23, 2001 8:21 PM
Subject: RE: [RFI] VHF-AM radios

> Those of us who used to operate 2m AM (eons ago) know that it is possible
> to use a technique called "slope detection" to copy FM sigs with an AM
> receiver.  This does require being able to CAREFULLY and SLOWLY tune the
> receiver so that you can locate the center of the IF on either side of the
> FM carrier (the "slope") where the changes in deviation "swing" (which are
> a phase change) produce a limited amount of amplitude change.  I have no
> clue if the sets under discussion employ that technique, but they might.
> 73, Dale

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