Hi,
Back to an old thread from a couple weeks ago:
I run MMTTY with AFSK, almost all S&P both in and out of contests. I keep
the AFC OFF and pop it ON only if I need it for some reason. I have the
SHIFT set to FREE and if I'm having trouble tuning in a station (for
whatever reason) I click the AFC ON and see if it will fine tune for me. The
instant I'm happy, back OFF it goes. This will handle unusual shifts,
although
if the signals are very weak it may not work well.
When the QSO is over, I click HAM to put things back to normal again.
Do not run with AFC ON and the shift freewheeling. It may stay reasonably
close to 170 Hz by locking to those you are working, but you can end up
with a random shift and people will say your mother dresses you funny and no
one will like you.
73,
Kermit, AB1J
In a message dated 6/9/2011 11:59:14 A.M. GMT Standard Time,
psussman@pactor.com writes:
I've noticed over the years that some manufacturers (for whatever reason)
have moved to use a 200Hz shift instead of the standard 170Hz shift. The
reason for the move is unclear, perhaps it is merely for simplicity.
Whatever the case, it is claimed that tuning between two stations, one
using 170Hz shift and the other using 200Hz, is not all that great. When
the tuning between the two is centered, there is an offset of only 15Hz.
(200-170 = 30; 30/2 = 15) In the days when filters were a lot broader,
this offset was insignificant. I think Chen will bear me out that under
strong signal conditions this offset doesn't matter.
The only time when such an offset is important is when very sharp filters
with tight skirts are used AND the signal strength is weak or fluctuating.
That would lead to more errors.
I've been using an SCS modem for years with 200Hz shift on AFSK and I don't
seem to have a problem decoding weak RTTY signals.
Any thoughts or explanation?
Thanks,
73 de Phil - N8PS
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