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I still see these data signals as a waste of time
since had the carrier been keyed I could read them 100% without having to wait
for the right circumstance to get a decode, no need for level 2
demodulation.
There are several traces now visible but only an
odd decode!!!!!!!!!!!!!!! Try a QRS or CW QSO if you need an
immdediate report. These signals are audible with me.
g3kev
----- Original Message -----
Sent: Saturday, January 23, 2010 4:52
PM
Subject: Re: LF: JT4A simple guide?
Ok, fully understand Andy. Jim G7NKS is sending JT4A but
I'm not getting any decodes yet.
Roger G3XBM
On 23 January 2010 16:38, Andy Talbot <[email protected]>
wrote:
After posting that, I realised the JT4 PIC/DDS beacon code is designed
for 100% duty cycle operation, viz JT4, CW + carrier, which is a bit
antisocial (certainly the wide bandwidth CW bit). And more
importantly, as my PA is a low efficiency clas AB linear one - enough
said...
To adapt for low duty cycle would need the PIC code changing, so will
put the idea on hold unles there is a real demand. For a beacon,
WSPR has more to offer anyway.
Incidently, WSPR and JT4 are the same mode anyway, albeit with a
bandwidth change from 1.46 to 4.375Hz with a resulting 4.75dB
reduction in S/N. The coding and demodulation are all the same, so
this bandwidth difference should be directly detectable between
the two modes. The differing message contents wont affect the
efficiency, its the added error correction , sync and modulation that
matters - and they use the same algorithm.
On 23 January 2010 14:43, Roger Lapthorn <[email protected]> wrote:
Thanks
for this help Andy.
I'd not like to derive others of your valuable
500kHz WSPR beacon, but could you beacon in JT4A at certain pre-arranged
times or days perhaps? If JT4A looks like offering the possibility of
really weak signal QSOs to people like me running flea-power then I'd like
to explore the mode some more and having a reliable signal to test with
initially would be useful. I am sure there will be others who would value
this too.
73s
Roger G3XBM
On 23 January 2010 14:26, Andy Talbot <[email protected]> wrote:
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 www.g4jnt.comThis email has been scanned for
damaging side-effects by the health and safety police, is guaranteed to
contain no substances hazardous to health, but may contribute to
dissolving the nether and polar regions
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
http://www.youtube.com/user/G3XBM
G3XBM
GQRP 1678 ISWL
G11088
-- http://g3xbm-qrp.blogspot.com/http://www.g3xbm.co.ukhttp://www.youtube.com/user/G3XBMG3XBM
GQRP 1678 ISWL
G11088
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/G3XBM
G3XBM
GQRP 1678 ISWL
G11088
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