So 'JNT was visible and understandable then :-)
I was finishing off the DFCW software for the DDS module after seeing
Laurie's signal in real time, and modding it so gap length could be
programmed separately to dot length. This was the first time I'd seen a
proper DFCW transmission and hadn't known what to make the software do in a
previous version.
The aim with a signalling system like this is to maximise transmission time
and duty cycle. No information is transmitted when the transmitter is off,
so inter symbol gaps need to be just short enough to minimise specctral
spreading at the frequency shift point. For these transmissions an inter
symbol gap of 5 seconds, ie. 8% of the symbol length is used. Letter gaps
remain at one dot length, word gaps at two.
For looking back at the file, Larry, That transmission was from 1930z to
2256z DFCW at 0.2Hz shift using 60s dot periods with occasional breaks as
software changes to modify the format were introduced. Then from 0645z
until (still transmitting at 0950z) using 0.05HZ shift DFCW again 60s dots.
But rain makes makes the antenna less efficient so I'm 3dB down on the
earlier transmission.
For anyone with a 'JNT DDS module (about 60 have been sold since the RadCom
article appeared) the S/W is available, just ask.
Andy G4JNT
-----Original Message-----
From: [email protected] <[email protected]>
To: [email protected] <[email protected]>
Date: 04 February 2001 02:00
Subject: LF: Signals around 135.923
Hi group,
thats a nice image on Argo tonight at 22:45, with seven closely cuddled
stations:
925.0 weak carrier
924.15 ZP(V)? 10s/dot (good signal, but too fast for 21mHz)
923.4 G3XDV 10s/dot
923.0 M0BMU
922.5 G3XTZ
922.3 G3YXM
921.7/.8 G3AQC DFCW (slightly unstable)
921.4/.6 G4JNT DFCW (0.4 Hz shift earlier, then changed to 0.2)
The weak calibration dots at the right side of the image are 1 Hz lines
from
HBG after switching to 75 kHz.
73s de Markus, DF6NM
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