Path: nntp.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: "Don" <g@crcomp.net>
Newsgroups: sci.electronics.design
Subject: Re: Phase or frequency modulation?
Supersedes: <20250707a@crcomp.net>
Date: Mon, 7 Jul 2025 13:41:52 -0000 (UTC)
Organization: A noiseless patient Spider
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Message-ID: <20250707b@crcomp.net>
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Correction. <https://www.sigidwiki.com/wiki/Database> includes one
PM zombie satellite: <https://www.sigidwiki.com/wiki/Transit_5B-5>

Liz Tuddenham wrote:
> I have been checking the performance of a variable-reactance type of
> frequency modulator which 'pulls' a crystal oscillator.  After
> multiplication and mixing, the signal appears at 145 Mc/s.
>
> Listening to this signal on an Icom 706 MkII transceiver I found it was
> barely intelligible, with severe high frequency cut.  At first I
> suspected my modulator but I checked the audio output of the Icom with a
> good-quality signal generator and found the response was:
>
> 200c/s : -3dB
> 400c/s :  0dB
> 750c/s : -3dB
> 1 Kc/s : -6dB
> 1k5    : -10dB
> 2k0    : -13dB
> 2k5    : -16dB
> 3k0    : -18dB
>
> (Using the wideband FM setting of the Icom produced similar results, so
> the limitation was in the detector/A.F. stages, not in the I.F. filter)
> This looks as though EITHER a 6dB per octave response is being imposed
> on the output of the FM detector OR the detector is expecting phase
> modulation.
>
> The handbook for the Icom refers throughout to frequency modulation and
> does not mention phase modulation.  Most references to modulation in the
> 2-metre band (144-146 Mc/s in the U.K.) mention frequency modulation and
> the use of phase modulation would cause 'splash' into adjacent channels
> at higher audio frequencies because of the rising characteristic.
>
> Has my Icom been designed for a market where phase modulation is the
> norm or is there another explantion?

Good question. It's a shame the All Identified Signals database
<https://www.sigidwiki.com/wiki/Database> lacks a filter for PM mode.
Otherwise it might indicate countries where PM is popular.

Danke,

-- 
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.