[Fwd: LF: Lets use technology a bit more.]
Wed, 06 Jan 1999 07:44:58 -0500
> > G3LDO Wrote..
> >I find that a combination of Videography and normal CW is the best
> >mode for the 136kHz band
> Only if you want to keep to simple equipment, and stagnate.
> Videography is handicapped by the incoherent power detection employed in
> waterfall displays, the same data rate / bandwidth combination will give at
> least 6dB (from theory), and probably nearer 10dB (based on eyeball tests on
> waterfalls of known S/N ratios), if used coherently.
> There are much better modes around for a long time PSK31 (which we all know
> about now from RadCom) will beat CW, hands down, occupying just 31 Hz
> bandwidth with coherent detection. cf Aural CW with about 50 - 100 Hz
> bandwidth (the good CW operators ear is about this) and incoherent detection.
> Less optimum PSK can be generated very easily on this band with VE2IQ's
> 'COHERENT' software. This will allow BPSK communication at rates getting
> down to sub Hz bandwidths. At its higher data rates it is not as good as
> PSK31 due to the non optimum pulse shaping; at least in the older version of
> this software I have used on 73kHz. A new version using the Soundblaster to
> generate a Tx waveform is available but haven't looked at that yet.
> However, this later version and PSK31 require a mixer type transmit driver -
> ie an SSB transmitter. With the ready availbility of 455 kHz filters, a
> simple SSB driver for the LF bands is hardly a challenge these days.
> Lets get a bit of up to date technology into the LF scene now and open up
> the modes that might make UK - USA possible. If 1800km can be done with
> incoherent CW methods, then 1 bit / second PSK ought to reach the USA with
> the same margins. At least from the 1 Watt ERP people!
> Or does everyone just want to operate these days and not do any
> experimentation - seems to be the impression I get by reading the reflector
> these days. No wonder many of us experimenters don't even subscribe any more!
> If there is sufficient demand for a linear driver design, I'll try to
> produce a standard simple design using off-the-shelf filters. But why not
> transvert from HF ?
> Andy G4JNT / G8IMR