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This is one of the arguments that have appeared on this
reflector from time to time. Producing the tones in a coherent manner as
you suggest would have athe advantages you mention for ultra narrow detection,
but this technique is using the signalling waveform in a way it was not intended
! To produce seven phase coherent on-off keyed tones would require
seven locked oscillators - trivial when using a DSP approach to generate the
waveform by just maintaining seven Numerical Controlled Oscillators in software
and switching between their outputs, but very complicated to do with a direct
RF generated carrier.
I will run this again tomorrow and over part of teh weekend
with a longer more meaningful message; the phase coherent GPS locked signalling
is on hold for a couple of days so can carry on with this
mode.
Andy G4JNT
-----Andy, is it possible to let the TX run
tomorrow (friday) evening ?
I would like to try again from the club
station where the noise is much lower than here at home.
The strong
local noise brought up this idea:
If the seven tones were transmitted
in a "coherent" way (for each tone), so one could DETECT THE PRESENCE of such
a signal (instead of decoding it) ? This way, if one used a waterfall with say
5-minute scrolling interval and a frequency resolution of a few millihertz,
seven lines would grow out of the noise giving a coarse figure how many dBs
are missing until DECODING is possible.
I once observed a CW qso between
two stations with a very slow ("high-res") waterfall, one station produced a
very sharp line on the display while the other (though very stable in
frequency) did not. The same effect could be observed on Rik's proposed mode,
depending on how the signals are generated... but I don't want anyone trying
to key the output of seven independent DDS'es. There must be a smarter way (if
the "coherent" transmission makes sense at
all
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