From: Jonathan Naylor (tfuyrlzn@pfankuch.com)
Date: Wed Aug 21 2002 - 00:06:37 EEST
Hi All
A little status report on the progress of JT44 for Linux.
What does it do now:
Transmits JT44 and FSK441 (WSJT decode is perfect)
Has timing control for both modes
Can use soundcards in 16-bit or 8-bit mode
Can read/write WAV files in 16-bit or 8-bit formats
Can use the serial, parallel or no ports for TX switching
What doesn't it do at the moment:
No receive capability for either mode
No GUI (will probably use KDE/Qt)
The development is being done slowly as I am learning at the same time.
The receive side is much more complex that the transmit side since (at
least for JT44) you have time and frequency correlation which is not
trivial, I am hoping Bob K1JT can provide pointers to how he did it in
his WSJT program.
I had to change my tone generation from an IFFT to a Numerically
Controlled Oscillator because the symbol length is not a power of 2.
However the NCO is probably more efficient in terms of CPU and is
performing well. I have started on the JT44 receive, I have a sliding
FFT which is producing lots of data and its quite interesting to see
the symbols appearing in the "bins".
My plan is to have two programs, one for JT44 and one for FSK441, with
priority being given to JT44. In the GUI I will probably not include
the information about Sun and Moon positions as there are other
programs which do that better. I am going to follow the UNIX principle
of one program for one task, even if I have to write the adjunct
programs.
My plans are intitally to have a simple text based user interface until
such time as I am happy with the operation of the underlying signal
processing. The GUI will probably be written in KDE/Qt as that has
native C++ bindings.
The whole thing is written in C++ and I am taking time to provide a
good framework for doing further development of new weak signal
protocols. A case that comes to mind is a protocol that is more
suitable for EME on frequencies higher than 1296 MHz where the
scintillation causes frequency spreading which can make the JT44 signal
spread over more than one receiving bin. Something more akin to slowed
down FSK441 with fewer tones and greater spacing is possibly more
suited to that task. The test of the framework was that I was able to
implement FSK441 transmit about one hour after I had JT44 transmit
working.
This is a lot of fun to work on, and a learning experience. I hope that
the lack of replies about JT44 on Linux is more to do with their having
been an EME conference this weekend rather than no-one being
interested. As previously stated all of my work is under the GPL and is
free to have and to modify. If anyone is interested in having it, drop
me a line. In theory you could use Linux JT44 transmit and Windows
receive, I can't wait to hear of the first QSO off the moon with it !
My priority is to work on JT44 and then FSK441 later. After listening
to the monkey house on 144.370 MHz during the Persieds, I am not sure
we need more operators on FSK441 in Europe, but as a technical
challenge it is very interesting.
73 to all
Jonathan HB9DRD/G4KLX
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