> Made me wonder though if one could decode two signals intertwined but > individual mark and spaces traces in the clear form each other?. I would > think it might be possible. Anybody done this?
RTTY tones have sidebands, and since the Tx logic is not usually shaped to move optimally between the tones, but instead tends to switch abruptly, each tone has sidebands beyond the minimum necessary. I've often thought it might be fun to create an FSK demodulator for systems that use more spacing than is needed (for 45.45 baud RTTY, that is about 30 Hz spacing) that would examine and attempt to demodulate using three parallel algorithms: 1) The typical differential amplitude algorithm using dual filters feeding a data rate filter and "slicing" the output. 2) A single tone amplitude algorithm using just the space tone filter and a reference derived from hi/low values in that filter (or some more-sophisticated sliding reference), feeding a data rate filter and slicer... 3) The same as 2, but using the mark tone filter only. In most cases, the first algorithm will give best results of the three. But in cases where signals are overlapping, or partially overlapping, or there is selective fading or QRM on one tone, the demodulator looking at the other tone is likely to give useful copy if the S/N is sufficient. Implemented in a PC with the three text streams aligned, it could make the difference between a contact or not, or a repeat or not. Stream it with the output from your DXP-38, also with text aligned... 73, Lyle KK7P ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
