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modtest4.txt
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1993-06-27
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Experimental EME transmit waveform
de AF9Y, June 27, 1993
The MODTEST4.EXE program allows a soundcard to drive the microphone
input of a transmitter with experimental modulation. The modulation
and coding has been designed specifically for EME channel
characteristics to take advantage of libration fading and accommodate
signal drift/dispersion. I have estimated the coding gain for the
ASCII encoded signal at aprox 10db better than a morse code signal for
the same transmitted letter. The transmitter should be in USB to
transmit the audio modulation from the Soundcard.
The program provides the following test signals in sequence :
1) 960 Hz Sinewave
2) 960 Hz Modulated with alternating 180 degree phase shifts
every 64 cycles (Binary PSK at 63 Cycles/chip)
3) 960 Hz Modulated with alternating 180 degree phase shifts
every 8 cycles (Binary PSK at 8 Cycles/chip)
4) 960 Hz Modulated as described in #3 above and coded for
a 63 chip Maximum Length Sequence (MLS) for each Bit. The
"one" bits have 7 chips at zero phase preceding the MLS.
Letters are separated with an additional 3 chips. Two
letters ("R" and "O") are repeatedly transmitted with this
coding until the program is terminated.
I will need some help with EMEers who can transmit the "RO" test
signal and record the results (as a .WAV file) on an EME path. The
record utilities that come with most sound cards in either Windows
or DOS should be OK as a .WAV recorder. Set the sample rate at 11K
or greater per second. This program does not run under DOS6's
memory manager in my system for some reason related to DMA
operation. I am still investigating that problem. QEMM works
fine.
More detail on the coding approach and techniques for decoding will
be provided as a text file at a later date. Those interested can
contact me via phone at 219-637-3399 (Home) or 219-487-6041 (Work).
I can also be reached on the 2mtr EME net (14.345 Mhz), weekends
between aprox 1700-1830 GMT.
Thanks de Mike, AF9Y