From Signal Identification Wiki
THROB is a unique data mode that relies heavily on DSP techniques. THROB was created by Lionel Sear, G3PPT.
THROB uses 9 tones, spaced 8 or 16Hz. THROBX, an evolution of THROB, uses 11 tones spaced 7.8125 or 15.625Hz.
- Hobby Level Software