On Fri, 15 Jun 2001 22:04:41 -0500, Don Hill AA5AU wrote:
>Some may argue
>that AFSK is for VHF only. Well, in today's HF digital world, AFSK
>means to you are sending audio to your radio and the audio shifts mark
>and space. FSK is when you send on/off keying to your radio and your
>radio does the frequency shift keying
_________________________________________________________
Don is right of course. The confusion between AFSK and FSK
started some years ago and now has become widespread. In the old
days, AFSK meant a carrier modulated by audio tones; this could
be either AM or FM. You transmitted a carrier and put the audio
tones into the mic connector. When SSB became popular, folks
figured out you could also use audio tones into the mic even
there was no carrier. However, the RF output was completely
different - in fact, RTTY done this way is indistinguishable from
what we know as FSK. But because the tones went into the mic
connector, they still called it AFSK.
FSK means a carrier which is shifted back and forth WITHOUT any
modulation at all. Putting audio tones into an SSB transmitter
actually gives you a true FSK signal, although it is commonly
called AFSK. The "real", old time AFSK is what is still used on
VHF for packet work - an FM carrier modulated with audio tones.
No wonder folks are confused!
If you'd like to learn more about the basics of RTTY, go to:
http://www.geocities.com/mmhamsoft/mmtty/help/RTTY-Basics.htm
There you'll find a tutorial called RTTY BASICS which I wrote for
the MMTTY program help files. Although it's oriented to MMTTY,
there is a lot of good information for everyone regardless of
software.
Hope all this helps.
73, Bill W7TI
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