DominoEX Modes






all signals shown in x2 waterfall mode, tick marks at 100 Hz intervals, waterfall palette is "blue-2"

General Description

DominoEX is a family of offset incremental multi-frequency shift keyed modes with low symbol rate. 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 is normally used without Forward Error Correction, as it is very 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, normally used without Forward Error Correction. The FEC option is rarely used. The default calling mode is DominoEX11.

Coding and Character Set

A nibble-based varicode with ASCII-256 user interface is used. Lower case characters are sent faster. An ASCII-128 secondary character set allows a fixed (typically ID) message to be sent whenever the transmitter is idle. Modulation is nibble-wise symbol synchronous, differential.

The FEC option uses a binary varicode with modified ASCII-128 user interface. Lower case characters are sent faster. Modulation uses two dibit pairs, symbol synchronous, differential.

The FEC option uses binary convolution to generate two dibits per varicode bit, and halves the corrected data rate for the same symbol rate. Rate R=1/2, Constraint length K=7, default Interleaver L=4 (16 bits). The default interleaver is too short for effective burst correction, and performs better with L=10 or more.

Operating Parameters
Mode Symbol Rate Typing Speed1 Duty Cycle2 Bandwidth3 ITU Designation4
DominoEX45 3.90625 baud 29 wpm 100% 173 Hz 173HF1B
DominoEX55 5.3833 baud 44 wpm 100% 244 Hz 244HF1B
DominoEX85 7.8125 baud 58 wpm 100% 346 Hz 346HF1B
DominoEX116 10.766 baud 80 wpm 100% 262 Hz 262HF1B
DominoEX16 15.625 baud 115 wpm 100% 355 Hz 355HF1B
DominoEX22 21.533 baud 160 wpm 100% 524 Hz 524HF1B


1.  WPM is based on an average 5 characters per word, plus word space. Values based on sending 100 "paris " words.
2. Transmitter average power output relative to a constant carrier of the same PEP value.
3. This is the "Necessary Bandwidth" as defined by the ITU.
4. A summary of the ITU Designation system can be found at

5. Double spaced mode.
6. Default and normal calling mode.