Fldigi Users Manual  4.1.17

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:

Throb baud rates and tone spacings

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

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