ORIGINAL MESSAGE:
On Tue, 23 Aug 2011 20:45:36 -0400, Ed <autek@comcast.net> wrote:
>
>Then exactly what is the true definition of FSK ?
REPLY:
Please allow me to insert a short history lesson here. The term "AFSK" as we
commonly use it on the HF bands is not really correct, historically speaking.
Way back, the original meaning of AFSK was a carrier, either AM or FM, which was
modulated with two audio tones. If you recall your modulation theory, this is
very different from shifting the carrier frequency back and forth by 170 Hz, as
we do it on HF today. AFSK is still commonly used on VHF packet and that is
"true" AFSK, since the FM carrier is m adulated with two audio tones. VHF packet
is emphatically not FSK.
Somewhere along the line, the term AFSK came to be used to describe audio tones
being used to modulate an SSB transmitter, which does in fact produce a
transmitted signal which is identical to a frequency-shifted carrier. This is
totally different from using audio tones to modulate an AM or FM transmitter,
but the distinction has gradually blurred over the years, unfortunately.
I am guilty of using the term wrongly myself, but it has become so embedded in
the ham culture that I doubt the error will ever be corrected. Just remember
that as we use the terms on HF, FSK and AFSK refer ONLY to the method of
generating the signal in your rig, not to the actual transmitted signal itself.
The signal that goes out over the air is identical, assuming the transmitter is
operated properly.
Hopefully this will clear up some of the confusion.
73, Bill W6WRT
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