DominoEX is a family of offset incremental MFSK (Multi-Frequency Shift Keying) 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.

Therefore MFSK is ideal for HF operation since it has good noise rejection and good immunity to most propagation distortion effects which adversely affect reception of other modes. MFSK is already used on HF by modes such as MFSK16, ALE, THROB and Olivia, but DominoEX improves on the MFSK types of modes by employing an Incremental Frequency Keying strategy. DominoEX is also a reasonably narrow-band mode along the lines of MFSK16 or RTTY.

A narrow-band application of MFSK presents some challenges. The main problem is that radio transceivers with high stability and tuning accuracy are usually required, since very small frequency steps are used for example when ompared with RTTY. MFSK is also prone to interference from data arriving from different ionospheric paths, and like many modes, it is prone to interference from fixed carriers within the data passband. Forward Error Correction (FEC) can be deployed to reduce errors, but such modes can become slow and difficult to operate or the modes consume an excessive an excessive amount of bandwidth. With DominoEX, a different approach was taken, concentrating on perfecting the design for best Near Vertical Incidence Signal or NVIS reception without requiring FEC. All the inherent MFSK problems are also avoided or much reduced.

DominoEX uses a series of new techniques to counter the general limitations of MFSK. To avoid tuning problems, IFK (Incremental Frequency Keying) is used, where the data is represented not by the frequency of each tone, but by the frequency difference between one tone and the next, an equivalent idea to differential PSK. An additional technique, called Offset Incremental Keying (IFK+) is used to manage the tone sequence in order to counter inter-symbol interference caused by multi-path reception. This gives the mode a great improvement in robustness.

Like Olivia MFSK, there are several variations of the DominoEX mode: DominoEX4, DominoEX5, DominoEX8, DominoEX11, DominoEX16 and finally DominoEX22. The higher the number the faster the speed of transmission so difficult conditions it may be wise to use the slower speed, while good conditions might allow for faster speeds.

DominoEx-4 test sample
DominoEx-8 test sample
DominiEx-16 test sample

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