FLDIGI Users Manual 4.0
The THROB family of modes use two tones at a time. These tones are also amplitude modulated and can be a single tone for some symbols.
The mode has no Forward Error Correction, and is difficult to tune. It is fairly sensitive and moderately robust. Keyboard-to-keyboard QSOs are reasonably fast.
Tuning must be very accurate, and the software will not tolerate differences between transmit and receive frequency.
The amplitude modulation component of THROB is a raised cosine AM modulation of each symbol. This combined with two tones transmitted at the same time, means that a very linear transmitter is required. It also gives the mode its very unique sound. You will never mistake Throb for any other mode.
For THROB, nine tones are used, spaced 8 or 16 Hz. For THROBX, 11 tones are used, spaced 7.8125 or 15.625 Hz.
Fldigi supports the following:
|Mode||Symbol Rate||Typing Speed||Bandwidth|
|THROB1||1.0 baud||1.0 cps (10 wpm)||72 Hz|
|THROB2||2.0 baud||2.0 cps (20 wpm)||72 Hz|
|THROB4||4.0 baud||4.0 cps (40 wpm)||144 Hz|
|THROBX1||1.0 baud||1.0 cps (10 wpm)||94 Hz|
|THROBX2||2.0 baud||2.0 cps (20 wpm)||94 Hz|
|THROBX4||4.0 baud||4.0 cps (40 wpm)||188 Hz|