Subj: New BPSK program available
Date: 98-02-11 17:35:33 EST
From: bill@ietc.ca (Bill de Carle)
Hi BPSK, LOWFER enthusiasts:
If you go to my web page: www.ietc.ca/home/bill/bbs.htm you will find a new program called AFRICA Version 1.0, which has lots of improvements over the old COHERENT program. The two systems are compatible - AFRICA talks to COHERENT and vice-versa.
Only problem: to run AFRICA you will need Pentium (or possibly a very fast 486). If you have a fast machine available for BPSK, why not download the new program and give it a try?
It features two decoders: the old system (COHERENT decoder) which decodes the incoming BPSK one bit at a time, and the new AFRICA decoder, which looks at the whole character, all bits at once. If the transmission channel does not introduce excessive phase distortion or flutter, the AFRICA algorithm can produce perfect copy on signals buried so far in the noise even COHERENT prints only garbage.
For use on HF, most paths most of the time will not be stable enough to show improved copy using AFRICA, so you can always use the older decoder. Going to higher speeds than we have been using might be another way to get away from the flutter problems.
AFRICA has a tracking filter which can compensate for any "constant" frequency error, as long as it changes only slowly or not at all. With the old program all signals had to be received at exactly 800.0 Hz or you got degraded copy. Of course the AFRICA algorithm front-end decoder has a bandwidth n times *narrower* than the COHERENT algorithm (n=10 for ASCII, 16 for ET1, 27 for ET2) - so unless the received signal is rock stable it will go outside the passband of the tracking filter a lot and you will be much better off using COHERENT. AFRICA should be ideal for groundwave copy of LOWFER signals where the phase is very stable. And for laser work.
The general idea is to start out a QSO on HF much as we have been doing with COHERENT, but once SYNC'd in and the tracking filter has locked onto the incoming carrier, you can switch over to the AFRICA algorithm to see if it improves copy - with just a click of your mouse! No need to re-sync, it doesn't even lose a single character of the incoming message.
I'd appreciate any feedback on this new program.
Thanks,
73 de Bill VE2IQ
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