AFAIK The is no 'simple guide' JT4x was never originally
going to be one of Joe's supported modes, although after our extensive
use on uWaves it certainly is now. JT65x was the
more popular and documented code, being heavily used for EME on 144 /
432 / 1296MHz, with JT4x just one of those included in
the WSJT suite to 'try out' If you download and read the
WSJT users guide and other supporting files, there's all you
need to know to get it going is in there.
Its still debatable as to whether JT4 is better or worse than JT65x,
but at least it does have the options of being available in a range of
bandwidths / tone spacings making it usable from DC to red
light. (Although I think I've only ever come across A, D and G
being used respectively on LF, HF and uWaves) There's
probably only a fraction of a dB in it and both are, as far as I can
ascertain, only a dB or two away from the Shannon limit. [Which
knocks spots off CW or any fuzzy mode, as well as straight
PSKnn without error correction]. Wolf has a similar
signalling efficiency, but unfortunately is wider, needs a linear TX to
avoid being too wide and seems less user friendly.
A year or so ago we (the microwave community) wanted something for
use on 1.3GHz and up to 10GHz or beyond. JT4G, the widest
spaced varient of them looked suitable. After some
prompting, Joe was persuaded not to abandon that mode, and in
fact he modified the code to enhance the decoder routine
so the wide spaced version would be decoded with the same S/N as
JT4A. We discovered just how good the mode was, even
under severe rainscatter conditions where each tone was spread out to
200Hz bandwidth (tone spacing in JT4G is 315Hz for 1kH zwide overall, so
this rain scattered signal still had discrete tone energy).
There are now two microwave beacons that transmit JT4G
waveforms, the 10 and 2.3GHz ones in Dorset GB3SCX and
GB3SCS
www.scrbg.org and now GB3CSB on
1.3GHz from central Scotland
http://www.rayjames.biz/gm4cxm/id14.html Other
will follow before long as it is quite an easy mode to generate from a
simple PIC keyer provided accurate timing information is available to keep
it synched.
My beacon engine - the one that currently drives the 503.7/503.85
signals - can give JT4A immediately just by reprogramming the
PIC. Would there be any interest, bearing in mind both
the WSPR and "5MHz type" waveforms will be lost for the
duration?
Andy
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On 23 January 2010 13:48, Roger Lapthorn
<[email protected]> wrote:
Having
looked on the WSJT website there is little (no?) reference to JT4A
in the help files. I assume it is similar to modes like JT6M which I
have managed to receive in the past on 50MHz but never tried
TXing.
Can someone point me in the direction of a "JT4A for
Dummies" guide, or something similar that I might understand,
please?
73s
Roger G3XBM
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
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