>>>AA6YQ comments below
-----Original Message-----
From: rtty-bounces@contesting.com [mailto:rtty-bounces@contesting.com]On
Behalf Of Kok Chen
Sent: Tuesday, January 27, 2009 11:37 PM
To: RTTY Mailing List
Subject: Re: [RTTY] Best RTTY Program
>snip<
In software, extra demodulators also cost nothing; it is not like you
have to shell out $4000 to HAL for each one -- I simply instantiated
more copies of a modem object (Obective-C is object oriented). What
cocoaModem does is to run 9 FSK demodulators behind your back, then
use majority voting (9 is an odd number by design) to decide which
character it prints to the screen. Each demodulator has a slightly
different ATC time constant and relative multipath delay. You don't
have to keep an eye on multiple screens or windows, the majority
voting module does it for you.
The majority is not always right of course, but they are right enough
times to make it worth spending all the extra processor cycles. This
also has an additional advantage that I use this for squelching. The
more demodulators have a character in common, the less the chance the
character is squelched away. The squelch slider is simply a value of
how many demodulators must agree for the character to print.
It is probably trivial to add to MMTTY, by the way :-). Just run each
demodulator with a slightly different "MMTTY parameter." Then use an
HF channel simulator to decide what sets of parameters you want to use.
>>>MMTTY includes two kinds of modulators -- a frequency discriminator and a
PLL -- so more variations are possible. On the other hand, a variation only
adds value if it at least occasionally produces better results than its
competitors, so some work with a channel simulator would be in order.
73,
Dave, AA6YQ
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