[50mhz] Re: [Moon-Net] JT-44 Simulation

[Lance Collister]

Roger Rehr W3SZ wrote:
> 
> Hello, All!
> 
> If you don't want to think about JT-44 delete this now.
> 
> It's been really nice to see all of the JT-44 EME activity springing up, and
> reading about the low power contacts.
> 
> I wanted to play with JT-44 with 'known' signal and noise levels a little
> bit, under conditions that were stable during the observation period, to see
> what it really could do, so I lashed together a bench setup where I used one
> computer as the JT44 transmitter, and another as the JT44 receiver, with
> varying signal to noise ratios produced by varying the JT44 signal strength
> in the presence of bandnoise.  I put some of these results on a web page,
> including the wave files of the 'received' signals, a listing of the signal
> and noise levels used in the experiment (measured with Spectrogram), some
> FFTDSP files generated at various signal to noise ratios, and notes on the
> level of JT44 performance at each level and notes on the audibility of the
> signals at each level (admittedly subjective).  Anyone can repeat the
> experiment by downloading the wave files and running them thru their own
> copy of WSJT, if desired.  I found this very interesting to do, and hope
> others will find it interesting to see.
> 
> My (small) EME JT-44 experience is confirmed with this experiment:
> 
> The signal is below the noise level (I know because I put it there, and
> documented it)
> The signal can't be seen on FFTDSP
> The signal can't be heard
> Yet JT44 copies it
> 
> Cool!
> 
> 73,
> 
> Roger Rehr
> W3SZ   FN20ah
> 2 Merrymount Road
> Reading, PA  19609-1718
> http://www.qsl.net/w3sz
> 
> _______________________________________________
> Moon-Net posting and subscription instructions are at http://www.nlsa.com/nets/moon-net-help.html

TNX, Roger!  This type of confirmation and experimentation is very valuable to many
of us who are trying to get going with this new mode.  I have 6m EME skeds with it
later today and will be watching the input audio also with Spectran to see if I
detect any traces.  Most of the stations I have run with on 6m EME have shown up as
weak traces on Spectran, but have not peaked strong enough for a contact - or have
moved frequency so they were out of my narrow DSP audio filter at the brief moment
when their signals peaked above the noise floor.

It is totally amazing to me to imagine reaching down to complete a contact with a
signal that does not even display a trace on the computer screen, and this is
precisely what is keeping me going on the JT44 effort.  If it can work with the
unsteady, erratic, and 6m EME signals that always seem too weak to copy, it could
open up a new dimension for 6m propagation around the world.  

It is very exciting to be able to experiment with such a great tool.  VY 73, Lance



 
-- 
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: (406) 626-5728   FAX:(406) 728-6320
URL: http://www.bigskyspaces.com/w7gj