[Fwd: LF: Lets use technology a bit more.]
Wed, 6 Jan 1999 22:07:20 +0000 (GMT)
I think there is a good message here. There is a lot AMRAD could do to
improve the backend of these LF systems with new technology. Once we get
a good handle on the basics, these kind of things could be a fruitful
future direction. I think high rate coding could add a number of db (64
rate codes, for example).
On Wed, 6 Jan 1999, Andre' Kesteloot wrote:
> firstname.lastname@example.org wrote:
> > > 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