MFSK mode other than mfsk8 and 16
These are unconnected, manually controlled message asynchronous symbol synchronous simplex chat modes, with full-time Forward Error Correction. MFSK tone spacing is in both cases equal to the symbol rate (15.625 Hz and 7.8125 Hz). In order to maintain sync during idle periods, every few seconds a few non-printing characters is sent. The default calling mode is MFSK16.
MFSK16 also has an image transfer mode. This is controlled and triggered from MFSK16, and will transmit B&W or Colour pictures of any size and shape, although smaller is better, as transmission is only 1000 pixels/sec. This image transmission is an analog mode without sync. The image transmission is FSK of the same bandwidth as MFSK16, and again transmitter linearity is unimportant.
Coding and Character Set
A nibble-based varicode with ASCII-256 user interface is used. Lower case characters are sent faster. Modulation is four or five bit symbol synchronous, and in MFSK16 the dibit order is determined automatically. MFSK8 has five bits per symbol and uses an extra trial Viterbi decoder to determine the correct bit order.
The FEC uses binary convolution to generate two dibits per varicode bit. Rate R=1/2, Constraint Length K=7, Interleaver L=10 (40 bits). A matrix interleaver is used. This is a standard NASA design.
I think the 64L and 128L is using FEC with also a long interleaving techinque
Mode Symbol Rate Typing Speed1 Duty Cycle2 Modulation Bandwidth3 ITU Designation4
MFSK4 3.906 18 wpm 100% 32-FSK 154 Hz 154HF1B
MFSK11 10.767 baud 40 wpm 100% 16-FSK 218 Hz 218HF1B
MFSK22 21.533 baud 80 wpm 100% 16-FSK 435 Hz 435HF1B
MFSK31 31.250 baud 55 wpm 100% 8-FSK 330 Hz 330HF1B
MFSK32 31.250 baud 120 wpm 100% 16-FSK 630 Hz 630HF1B
MFSK64 62.500 baud 240 wpm 100% 16-FSK 1260 Hz 1260HF1B
MFSK Image 1000 px/sec 128x128 B&W 16 sec 100% Analog FSK 316 Hz 316HF1C
MFSK128 125 480 100.00% 1920 1920HF1B
MFSK64L 63 240 100.00% 1260 16-FSK 1260HF1B
MFSK128L 125 480 100.00% 1920 1920HF1B