On Jan 27, 2010, at 8:32 PM, Bill, W6WRT wrote:
> Do you think it might be DominoEX? Are there any
> drawbacks to using it in a contest? If it is slower that is not
> necessarily a gad thing if throughput is significantly better.
I don't know if DominoEX will gather steam or fizzle away like the other
digital mode-du-jour. It certainly has many unique features to earn a position
in amateur history. I personally think ZL1BPU did a fantastic job with it
(Murray was also the one who came up with the MFSK16 protocol).
ZL1BPU came up with the IFK scheme in DominoEX to counter the usual criticism
of how slowly MFSK16 tunes (and created non-FEC modes to further improve the
decoding latency). It uses a nibble mode Varicode, which makes much more sense
than binary Varicode for 16 tone FSK (DominoEX actually uses 18 tones to make
sure that successive ones are separated by at least 2 tone slots to avoid
intersymbol overlaps that are caused by doppler spreading). Instead of an idle
varicode or a diddle character, Murray used the idle periods to transmit a
secondary code set which can be used as a beacon (you can send your callsign
repeatedly in the beacon channel, for example, or hey, even a row of unending
dots to irritate Phil, GU0SUP :-) :-)
Skip KH6TY is pushing its use as an FM weak signal mode on VHF (i.e., use the
audio tones to modulate an FM transmitter instead of an SSB transmitter).
Speed wise, it has many submodes, from DominoEX 22 down to DominoEX 4. When
you add FEC, it becomes about a factor of two slower than non-FEC versions in
terms of thruput. To get a bird's eye view of the non-FEC speed, take a look
at the first chart here
http://homepage.mac.com/chen/w7ay/cocoaModem/UsersManual/mfskManual/mfskManual/dominoex.html
The second chart on that page gives a 10,000 ft view of how non-FEC DominoEX
performs against BPSK31 (for the same speed, it is perhaps 2 dB more sensitive
than BPSK31 under quiet band conditions).
Details of FEC performance under poor propagation can be found here
http://homepage.mac.com/chen/Technical/DominoEX/ITU/index.html
If you compare the DominoEX 8 (with default FEC flutter -- red curve) chart here
http://homepage.mac.com/chen/Technical/DominoEX/ITU/ITU/flutter.html
with the VE3NEA's RTTY flutter chart here,
http://www.dxatlas.com/RttyCompare/
you can see that DominoEX 8 with FEC a whopping 11 to 12 dB advantage compared
to RTTY. That is a power difference between an over 1 kilowatt transmitter
and a 100 watt transmitter.
VE3NEA's RTTY and my DominoEX charts are pretty much directly comparable since
we both use a reference of 3 kHz noise bandwidth. Both were measured using real
world modems, using the same Watterson HF channel simulator models and CCIR
parameters (the simulator implementations were different: Alex used PathSim and
I used cocoaPath).
With FEC turned on, DominoEX 8 does run only at about half the output character
rate of RTTY. But that 12 dB is hard to argue against when conditions become
bad. When conditions are good, turn the FEC off and get that factor of two
back.
The slower DominoEX modes are even better, but they are probably too slow for
people who are used to playing RTTY. But if you are interested in beating
RTTY by only 6 dB, you can use the DominoEX modes that are faster than 45.45
baud RTTY :-).
I don't know if KH6TY will succeed in giving DominoEX better visibility, and
even if he does, if its success in the VHF/FM weak signal world will translate
into success in the HF bands. DominoEX has been around for a while now and
never took off.
If I remember correctly, PSK31 was not very popular either in the earlier
years, until the same KH6TY introduced waterfall tuning to PSK31 with his
DigiPan program. Once tuning became easy, PSK31's use shot up like a hockey
stick.
73
Chen, W7AY
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