[RTTY] DominoEX, was: New Russian contest

[Kok Chen]

> 
> On Jun 5, 2016, at 11:03 AM, Bill Turner <dezrat at outlook.com> wrote:
> 
> I have been playing with DominoEX using fldigi in
> recent weeks. Not a lot of activity but QSOs are good and solid even
> with very low power. 

Technically, DominoEX is probably my all-time favorite mode.

It has multiple speed selections, good error vs SNR, and the speed it can tune to a station is the best I have seen.  The latter is made possible because DominoEX uses 17 incremental tones instead of 16 fixed codes; with good software, that extra tone in the pattern allows the receiver to zero in to the passband almost instantaneously.

In the presence of flutter, DominoEX 8 needs 16 dB (!) less transmit power to do as well as 45.45 baud RTTY:

http://www.w7ay.net/site/Applications/cocoaModem/UsersManual/mfskManual/mfskManual/dominoex.html#characteristics

Here are some of my measurements for various ITU propagation models

http://www.w7ay.net/site/Technical/DominoEX/Measurements/itu.html

And for AWGN:

http://www.w7ay.net/site/Technical/DominoEX/Measurements/awgn.html

The tone coding that DominoEX uses makes it very good when there is a lot of Doppler spreading (it never transmits a tone that is adjacent to a previous tone), so spectrum smearing does not faze it).  It can dig out a signal that is so weak that I created a special tool in cocoaModem just so that you can “see” the signal in the waterfall:

http://www.w7ay.net/site/Applications/cocoaModem/UsersManual/mfskManual/mfskManual/dominoex.html#weak

DominoEX' only weakness is the FEC mode.  The FEC convolution code is too short to help long fades and selective fades.  But that is not the fault of Murray ZL1BPU; someone else added the FEC to his original design, and that FEC became the defacto standard.  The FEC in MFSK16 is much better for HF propagation; MFSK16 is yet another of Murray’s design, but unfortunately suffers from difficulty to tune.

More recently, Murray took some of the better features from both MFSK16 and DominoEX and created a slow keyboard-to-keyboard FSQ mode:

http://www.qsl.net/zl1bpu/MFSK/FSQweb.htm

(FSQ is also described in the September 2015 issue of QST.)

I doubt any mode out there can outshoot DominoEX and FSQ for NVIS type propagation (tons of multipath).  Unfortunately, there has never been much DominoEX activity.  FSQ may get better treatment, but probably not, what with the rig merchants adding only PSK31 and RTTY decoders to their screens.

Oh yeah, I almost forgot, DominoEX has a very nifty feature: it does not transmit an idle symbol when you pause typing, like with the Idle Varicode in PSK31 and the diddle character in RTTY.  Instead, it encodes a slow beacon channel when you are not typing.  You can include some canned message (your callsign, your grid square, for example) and cocoaModem shows it as a horizontally scrolling “Times Square ticker tape":

http://www.w7ay.net/site/Applications/cocoaModem/UsersManual/mfskManual/mfskManual/dominoex.html#beacon

73
Chen, W7AY