[BC] FM Frequency Measurements...

[Burt I. Weiner]

Rick,

You are dead on with that comment.  I know of several people that 
claim to be able to measure (broadcast) FM with modulation.  The best 
they can hope to do is to measure the center of modulation.

The nature of a broadcast FM exciter is that it is not crystal 
controlled but crystal (or whatever) referenced.  This is pretty much 
by necessity.  If it were locked to a reference as hard as if it were 
actually trying to modulate a crystal, you'd be hard pressed to get 
the deviation without multiplying nearly a thousand times, like they 
did in the day's of yor.  My point is that when you have a Frequency 
Modulated Oscillator that is referenced to some source, it must have 
the ability to be "loosely" controlled by the reference, otherwise 
you have a crystal all over again.  This means that the AFC will be 
chasing the oscillator about as it's modulated.  This really shows up 
when you try and make accurate carrier frequency measurements.  With 
some exciters, if you quickly remove the modulation, the frequency 
will flail about for a second or two until it settles down.

Burt

At 05:10 PM 3/25/2007, you wrote:
>For FM
>(including TV aural) the key is dead air, and even that is harder to come by
>in this age of tight boards, with musical beds under so many spoken
>segments.
>
>Rick Levy
>Broadcast Signal Lab, LLP
>Cambridge, Mass.

Burt I. Weiner Associates
Broadcast Technical Services
Glendale, California  U.S.A.
biwa at earthlink.net
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