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From: "Don" <g@crcomp.net>
Newsgroups: sci.electronics.design
Subject: Re: Phase or frequency modulation?
Date: Wed, 9 Jul 2025 18:28:23 -0000 (UTC)
Organization: A noiseless patient Spider
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Liz Tuddenham wrote:
> Don wrote:
>> Liz Tuddenham wrote:
>> > Ralph Mowery wrote:
>> >> >> liz@poppyrecords.invalid.invalid says...
>> >> > Has my Icom been designed for a market where phase modulation is the
>> >> > norm or is there another explantion?
>> >>
>> >> Frequency and phase modulation should come out of a transmitter almost
>> >> identical.  As they start off different in the first stage of the
>> >> transmitter the audio frequency going into the modulastor stage must be
>> >> modified so the end results is the same for FM and PM.
>> >
>> > Yes - but it would appear that PM is the de-facto standard for
>> > commercially-built 'amateur' 2-metre transceivers despite all the
>> > literature calling it FM.
>>
>> Yes, your sentiment seems "on the money."
>>
>> This thread apparently advanced from an IC-706 to a DIY receiver. If
>> your schematic indeed pertains to your DIY receiver - excellent work
>> showcased in an excellent thread! (It taught me a few things, thank
>> you.)
>
> It is based on an idea that has been in the back of my mind for many
> years.  The change from an exchange-powered to a mains-dependent
> telephone service in the UK was the final factor that made me decide
> that I neded an alternative communications system.  I thought that,
> while I was making one, it might be a good idea if it was EMP-proof, so
> I decided it would have no semiconductors.  It has turned into an
> interesting project.
>
>> For what it's worth, the IC-706 probably uses the 75 micro-second pre-
>> emphasis standard prevalent in the Americas and Japan. Meanwhile,
>> Europe favors a 50 micro-second standard.
>
> Those are the standards for wide-band broadcast FM, but they are outside
> the range of permitted modulating frequencies for narrow-band amateur
> work.  The time constant for the Icom appears to be around 2000
> microseconds.
>
>> Although Phase Modulation is popular in Asia:
>>
>>     <https://pmc.ncbi.nlm.nih.gov/articles/PMC11501851/>
>>
>> it's doubtful the IC-706 was developed for an Asian market.
>
> Apparently it was.  There is a Japanese version with a slightly
> different specification from the European one.    You may have hit upon
> the real explanation, I haven't checked to see if mine is a Japanese one
> which has been sold in the UK by accident.

Dave Platt's "it's not a bug it's a feature" also makes a lot of sense.
I got on the wrong track in regards to standards after an attempt to
de-cipher repeater builder's cryptic warning about "Just watch the
pre-emphasis and de-emphasis!"

    IC-706 ... This is the HF radio that also does 6 meters.
    When coupled to a high-end repeater controller that
    understands what a HF remote base is (like an NHRC-10,
    an Arcom RC210 or similar capability controller) this
    makes a dandy HF remote base. Just watch the pre-emphasis
    and de-emphasis! ...

 	IC-706MKII ... This is the later 706 HF radio that also
 	does 6 meters and 2 meters. The same firmware bug that
 	affects the CTCSS frequency applies; use the same
 	procedure.

 	<https://www.repeater-builder.com/icom/icom-index.html>

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.