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THROB and THROBX are experimental multi-tone frequency shift keyed (MFSK) modes, good for low power transmission without being sensible to Doppler as are PSK transmissions. The use of raised cosine shaped tones pulses applied to each character gives a characteristic "throbbing" sound, hence the name of the modes. THROBX is an improved THROB mode but only for speeds of 1 and 2 bauds. The minimum Signal-to-Noise ratio is about - 18.5 dB for THROBX at 1 baud.
Created by : Lionel Sear G3PPT, in 2000 for THROB and 2003 for THROBX
Preliminary : THROBX is an evolution of THROB.
Description :
Baud rate : 1, 2 or 4 (1 or 2 in THROBX)
Speed : 10, 20 or 40 wpm (=10 x baud rate) or 60, 120 or 240 characters/min (=60 x baud rate) (10 or 20 wpm in THROBX)
Modulation : - for THROB: FSK 9 tones with 1 or 2 tones send in the same time (which give 45 possibilities including the idle tone)
- for THROBX: FSK 11 tones with 2 tones send at the same time (which give 55 possibilities including the 2 possible idle characters)

Reception mode: only one side (USB or LSB), USB is recommended
Character set : for THROB: 46 fixed length characters: A..Z 0..9 , . / ( ) ? @ = <SPACE> (with use of a shift character for ?@=). No error reset character.
: for THROBX: 53 characters: A..Z 0..9 , . / ( ) ? @ = # " + - ; : ! <SPACE> . No error reset character.
Shape of pulse : for the 1 or 2 bauds modes: rectangular at the center with leading and trailing quarters as raised cosine. For the 4 bauds mode (THROB only): raised cosine
Space between tones : for THROB: 8 Hz (1 or 2 bauds) or 16 Hz (4 bauds), for THROB: 7.8125 Hz ,
Bandwidth : for THROB: 72 Hz (1 or 2 bauds), 144 Hz (4 bauds), for THROBX: 94 Hz
Demodulation : non-coherent,
Synchronization : automatic on incoming throbs
Correction code : no
Convolution code : no
Interleaving : no
Automatic Frequency Correction : +/- 3 Hz,
Drift tolerance : 4 bauds: 40 Hz/mn max, 2 bauds: 20 Hz/mn max, 1 baud: 10 Hz/mn max according to signal-to-noise ratio,
Pmean/Ppeak : 0.35 for 1 and 2 bauds modes, 0.19 for 4 bauds
Lowest S/N : THROBX: -18,5 dB for the 1 baud, -17.5 dB for the 2 bauds
THROB: -16 dB for the 1 baud, -14.5 dB for the 2 bauds et -12 dB for the 4 bauds








Mode Menu
THROB & X
Mode Audio Sample
FFT Window Screenshot
throb4
throbx2
VIDEO OF AN ACTUAL QSO IN THROB HERE