ORIGINAL MESSAGE:
At 07:16 PM 1/8/2006, Chuck Brudtkuhl wrote:
> The observations regarding off frequency responses. I used to
> think this was getting to be the norm .. that and the move to 200
> hz shift due to the movement to TNCs. This off-frequency response
> (and wide shift) is VERY noticable when using a scope to
> tune. Often stations were so far off freq as to be out of my
> narrow receive band-pass.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I've noticed it too. I'm sure it happens because of incorrect use of
AFC. Here's how:
Station A has his AFC on while S&Ping, but is either not using NET or
is using FSK, which does not respond to NET. As he tunes across the
band, he finds station B calling CQ. He watches his tuning indicator
and when it shows B correctly tuned, he stops turning the knob.
Unknowingly, the AFC has "reached out" and tuned in station B before
his transceiver is actually tuned to B's frequency. A calls B
thinking he has him tuned in but A's TX is actually off frequency.
So how does A avoid this situation? Actually, there are two things to do:
1. Turn off AFC when S&Ping.
2. If using MMTTY, also click the "HAM" button to reset an changes
AFC has made.
The last one is vitally important. With MMTTY, when AFC tunes in a
signal, it changes the tune frequencies for MARK and SPACE. Just
turning AFC off does NOT reset them to the defaults, so one could go
merrily along tuning in stations off frequency and never notice it.
Been there, done that myself. :-)
AFC is great when CQing, but should never be used during S&P unless
one also uses NET. Note that NET only functions with AFSK, not with
FSK. It would be great if turning off AFC would automatically reset
the demodulator frequencies to the default. Perhaps I'll suggest that
to the author.
Bill, W6WRT
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