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NNTP-Posting-Date: Tue, 22 Oct 2002 10:51:49 -0500
From: email@example.com (John Fields)
Subject: Re: How does a mixer work?
Date: Tue, 22 Oct 2002 15:50:29 GMT
Organization: Austin Instruments, Inc.
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On Tue, 22 Oct 2002 13:27:13 GMT, Chuck Simmons
>AFC is not possible in SSB or independent sideband communication unless
>you put something in a sideband that can be recognized without a
>carrier. The FM stereo solution was to use a 38kHz carrier for AM
>modulation, suppress the carrier and then send a 19kHz "pilot tone" for
>carrier restoration. In HF independent sideband communication, at least
>in the 1960s when I was in that for a while, the trick was to agree with
>the distant end on what the carrier was. Both ends would set the
>carriers to the same frequency using frequency synthesizers. One type of
>synthesizer I used allowed 500Hz steps from 2 to 32 MHz (Collins) and
>another used 100Hz steps in the same HF range (TMC I think). It was
>rather funny when one end or the other had synthesizer trouble because
>it was sometimes hard to agree about who was wrong. The sidebands
>themselves do not even give a tiny clue as to what the carrier should
>be. I recall that particularly bitchy sites would complain if I had an
>error of only 10Hz in the transmission.
I don't know if it's old hat, but a method I worked out in the '60's
was to send a 1kHz signal and then have the far receiver tune its
VFO until the radio's audio output was precisely 1kHz.
Professional circuit designer
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