THOR is a family of offset incremental multi-frequency shift keyed modes with low symbol rate, closely related to DominoEX. A single carrier of constant amplitude is stepped between 18 tone frequencies in a constant phase manner. As a result, no unwanted sidebands are generated, and no special amplifier linearity requirements are necessary. The tones change according to an offset algorithm which ensures that no sequential tones are the same or adjacent in frequency, considerably enhancing the inter-symbol interference resistance to multi-path and Doppler effects.
The mode has full-time Forward Error Correction, so is extremely robust. The default speed (11 baud) was designed for NVIS conditions (80m at night), and other speeds suit weak signal LF, and high speed HF use. The use of incremental keying gives the mode complete immunity to transmitter-receiver frequency offset, drift and excellent rejection of propagation induced Doppler.
These are unconnected, manually controlled message asynchronous simplex chat modes, using binary convolutional Forward Error Correction. The default calling mode is THOR11.
Coding and Character Set
A binary varicode with ASCII-256 user interface (same as MFSK16) is used. Lower case characters are sent faster. An ASCII-128 secondary character set extension allows a fixed (typically ID) message to be sent whenever the transmitter is idle. Modulation uses two dibit pairs, symbol synchronous, differential.
The FEC system uses binary convolution to generate two dibits per varicode bit, and halves the corrected data rate compared to the equivalent DominoEX mode. Rate R=1/2, Constraint length K=7, Interleaver L=10 (40 bits).
Mode Symbol Rate Typing Speed1 Duty Cycle2 Bandwidth3 ITU Designation4
THOR45 3.90625 baud 14 wpm 100% 173 Hz 173HF1B
THOR55 5.3833 baud 22 wpm 100% 244 Hz 244HF1B
THOR85 7.8125 baud 28 wpm 100% 346 Hz 346HF1B
THOR116 10.766 baud 40 wpm 100% 262 Hz 262HF1B
THOR16 15.625 baud 58 wpm 100% 355 Hz 355HF1B
THOR22 21.533 baud 78 wpm 100% 524 Hz 524HF1B