Editor: ThrobV2.5 is an EXPERIMENTAL freeware Multi-Tone-Frequency- Shift-Keyed (MFSK) Transmission program evolved while experimenting with DSP on a PC soundcard. It uses a palette of 9 tones spaced 8 or 16 Hz apart giving a bandwidth of 72 or 144 Hz. There are enough permutations of the 9 tones when used as tone pairs and single tones to allow the encoding of a modest character set (See Code.) to be sent in a single tone PULSE. The tones are sent as a shaped pulse with the leading and trailing quarters raised cosine shaped, and the tones are received synchronously, with the synchronisation being set manually or automatically. There are three transmission speeds of 1, 2 and 4 Throbs/sec giving respectable transmission rates of 10, 20 and 40 wpm respectively. The 1 and 2 Throb/sec speed use a tone spacing of 8 Hz and a bandwidth of 72 Hz and the 4 Throb/sec speed uses a tone spacing of 16 Hz and a bandwidth of 144 Hz. There is potential to slow it down further for VLF etc. Throb2 evolved from Throb1, which used three consecutive pulses of 1 tone from a palette of 5. Throb1 had enormous limitations but showed that tone techniques can have advantages at low level, that amateur radio gear is able to function with techniques requiring a stability of 3 or 4 Hz, and that radio amateurs can readily use it. The use of raised cosine shaped tones gives a characteristic "throbbing" sound, hence the name of the method.
