[Laser] Troposcatter and Information Theory-2

[stjohn at ocsnet.net]

QRPp has a "warbler" system that works well with transmission reception below
the usual threshold.

Tom Upton  AD6N

"Andrew T. Flowers, K0SM" wrote:

> Bob,
>
> I've also had fun playing with Argo around here.  It's exactly that that
> put me on this project.  I am aware of the QRSS CW stuff that being used
> for Lowers here and 136Khz in the rest of the world.  CW and DFCW are
> still relatively inefficient compared pretty inefficent in terms of
> throughput compared to what you can get with a a multi-tone modulation
> scheme.  As an example, imagine that your communications path allows you
> to just barely communicate using the 3-second "dit" length using QRSS
> CW.  In this idea case, you could use frequency bins as small as 0.33Hz
> (I don't want to get into the keying sidebands due to OOK) and produce
> copy--either the bin has a signal in it or it doesn't, producing the
> "1's and 0's" that make up morse code.  Each character needs several
> bits before it is understood as a character--on average about 12 bits.
>  DFCW is a little faster since it converts all dashes (3 bits) to one
> bit.  It is more efficent to use the adjecent frequency bins and have
> one "bit" per character, thus improving throughput tremendously (or
> conversely, you could decrease the S/N and get the same throughput).
>
> The folks who brave LF have known this for a long time, though
> generating such a signal at RF with the accuracy and stability at RF is
> not a trivial task.  In those cases all you often have is a CW
> transmitter, so QRSSCW makes lots of sense.  For those with more
> elaborate setups, the coding scheme often has some sort of frequency
> synchonization to account for tunning differences.  While necessary, it
> does sacrifice S/N.  Neat stuff!
>
> Andy
>
> riese-k3djc at juno.com wrote:
>
> >Andy
> >
> >
> >I am not sure if you are aware of some of the existing QRSS programs or
> >not
> >these will go down to the milHz range and at 120 second dot length are
> >able
> >to go 30 Db under the noise to see the signal. The people that developed
> >the
> >programs may be able to help with your questions.. These programs are
> >used to
> >work on LF at 135 Khz as well as the band 160 to 190 Khz where part 15
> >operators
> >can run 1 watt to a 50 ft antenna, with these limitations beacons have
> >been copied
> >over a 1000 miles,, thats a really low ERP.
> >
> >suggest checking the Long Wave Club of America at
> >http://www.lwca.org/
> >you will find links to the software
> >
> >Using ARGO I have been able to copy the sub carrier of the ramsie Tx from
> >a double wall bounce
> >HAR ,,,,the Tx was in a different room and the dot was placed on a wall
> >reflected several times
> >before entering the shack and the K3GPG detector which directly fed my LF
> >converter, the soundcard
> >was fed by the IF rcv
> >
> >HAve Fun
> >
> >Bob  K3DJC
> >
>
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