Surprisingly, the KAM Plus can copy RTTY 23 very well, using their
"modem" mode and setting the difference between the Mark and
Space frequencies to about 23 Hz.
I copied MM0BQI/P on 20m with S2 on the S-Guesser, working
VE4COZ (who was much louder). Unfortunately, I am using FSK
(the internal AFSK generator of the FT-1000MP) and cannot
attempt a 2-way QSO. Just an SWL'er in this contest.
Tuning is very easy with the KAM's meter. Just as fast and easy as
tuning in a 170 Hz shift RTTY signal.
I think the reason a couple of people have complained about the
slow tuning is due to the tuning methods of many of the DSP
implementations.
Many DSP implementations would double-buffer the A/D conversion
buffers in too long a chunk. Thus, there is a long lag time before a
signal sample is given to the analysis phase. All this is in the name
of reducing CPU overhead of interrupt processing (hey, what else
is that extra processor speed used for, guys??!! I rather use it to
process interrupts than to have the CPU sit idly by.)
As a result, there is a lag time which shows up as a hysterisys in
the human eye-hand coordination. You need to tune at a much
slower rate across a signal than the lag time.
At 11025 Hz sampling rate, a 1024 byte buffer has a lag time
of more than a tenth of a second. This delay is too long for real time
interface.
Because of this, for my own DSP implementations, I have been using
very short buffers, no more than 256 bytes. And I send the data to the
tuning display's algorithms before I send them to be demodulated and
printed.
I had no trouble at all tuning in the RTTY 23 signals with the KAM, since
there is essentially no delay. I tune at the same rate that I tune a
regular
RTTY signal. The LEDs don't reach all the way to the two ends, but once
I can get it moderately, centered, the print just appears.
73
Chen, AA6TY
PS: Caveat -- my KAM Plus has been modified to raise the tank Q of
the switched capacitor filters. I doubt, though, that it made much of a
difference with copying such a narrow band signal as RTTY 23.
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