Interesting stuff, Bob.
From another angle, we went through last June with JT65 as the digital mode of
choice for DX. The minimum 4-minute QSO time was longer than many openings
lasted, thus there was a push for a quicker mode. Not sure why the
already-existing JT9 with its 15-second intervals wasn't promoted for this, but
I think that was also a strong impetus for the creation of FT8.
73, Dan
-----Original Message-----
From: k2drh <k2drh@frontiernet.net>
To: VHF Contesting Reflector <vhfcontesting@contesting.com>
Sent: Thu, Jun 14, 2018 12:14 pm
Subject: [VHFcontesting] How and Why Contest Mode Evolved
Maybe this will help folks understand how it works and also make other folks
understand why contest mode was necessary in the first place. The only thing
in the manual about Contest Mode is this:--------------------------------The
FT8 and MSK144 modes support a special feature allowing convenient transmission
and acknowledgment of four-character grid locators, the required exchanges in
most North American VHF contests. With this Contest Mode enabled, WSJT-X
supports messages of the form W9XYZ K1ABC R FN42 by converting the grid locator
to that of its diametrically opposite point on Earth. The receiving program
recognizes a locator implying a distance greater than 10,000 km, does the
reverse transformation, and inserts the implied “R”. Obviously, this mode
should not be used on the HF bands or under other circumstances where
world-wide propagation is possible.----------------------------------------This
leaves a lot unsaid. From the manual description all WSJTX messages are set in
a 72 bit format. The mode speed (fast or slow) determines how many times that
72 bit message is repeated in the transmission period. In FT8 its repeated
twice. If a single 72 bit message is received with no errors according to the
FEC (forward error correction method) then it will decode. No partial decodes
are allowed Joe did not include contest mode in the original alpha and beta
releases and it was added back some time ago well before (at least a year) FT8
was invented after a lot of stations complained about problems getting grids
across on MSK144 since grids were only included in TX1 and TX6. If you
scheduled a MSK144 QSO during a contest as we often do on Ping Jockey then both
stations would call each other with TX1. The standard operating practice says
as soon as you receive TX1 you respond with TX2. Well in that scenario only
one of the stations would actually receive a grid and this was not acceptable
since both stations have to exchange grids (but NOT reports) in a contest. Good
practice also mandates the exchange of acknowledgements or R. The only way to
legally do it then was to have both stations call CQ even on a prearranged sked
since TX6 had a grid in it, then when one received TX6 he would then switch to
TX1 and the QSO would progress. But it really wasn't the whole answer since you
really never acknowledge you received the other guys grid; it was just implied.
This also added another two sequence time interval to the QSO and both TX2 and
TX3 were superfluous to the contest QSO which only requires the exchange of
grids. Adding unnecessary sequences was a big burden since adequate meteor
burns can be scarce (especially on 2M) and sometimes you can go many minutes
without getting a ping that decodes. Additionally the older WSJT10 FSK441 mode
did have an alternate GRID only message format that was used during contests.
So there was a problem.-----------------------------So Joe want back to the
drawing board to try and accommodate the requests from contesters (myself among
them) to make this work better and shorter in MSK144 like it used to in FSK441.
But the 72 bit message format that is the basis of all WSJTX transmissions did
not allow that many bits to get the message with the format W4XXX K2DRH R EN41
encoded to be transmitted in 72 bits. So Joe had to do a work around or a
kludge (remember at this point in time Joe was pretty much doing all the
programming) and he had to do it quick because another contest was pending
(think he did it between June and CQWW VHF but my memory may be off). So he
came up with using the 180 degree around the world grid equivalent (or
reciprocal grid) being transmitted to keep within the 72 bit format ... and
then on the RX side of the program also in contest mode that is translated to
the correct grid on the screen. So this really was a solution to an actual
problem, albeit a messy one that creates compatibility issues between stations
that are not in contest mode. This translation to the alternate grid cannot be
implemented in the "normal" report mode because then it could not be used on HF
or even on 6M when multihop DX could be received.
---------------------------------------So why was contest mode put in FT8 and
why was it necessary to put the activation of it in the VHF UHF Microwave
settings? We were the ones who wanted to use FT8 in a VHF contest setting so
contest mode was grandfathered in from MSK144 during the beta testing stage.
As soon as it was many HF ops using FT8 failed prompt stupid and tried to use
it to shorten their QSOs despite the warnings that it could not be used for
international DX. They complained so much about the " funny grids" and
incompatibility with auto sequencing the programmers "hid" it from them where
only the VHFers who would use it could find it. During a contest if a station
CQs on FT8 in non contest mode and gets a TX1 reply they exchange grids and the
QSO is technically valid but the grids are not really acknowledged as good
practice would demand plus it takes an extra sequence with superfluous reports
to complete the QSO. If the other stations opts to send TX2 and replies in
"normal" or non contest mode then the CQ station does not get a grid. If the
other station calls him while he is engaged in another QSO in "normal" mode
then they did not actually exchange grids both ways during their QSO either;
even worse if he calls with TX2. And FT8 QSOs can be scheduled too ... around
here we do it on 2M. Contest mode on FT8 solves all these issues, works just
fine when both stations use it and satisfies all requirements. So saying that
contest mode is a solution in search of a problem is inaccurate and a
misunderstanding of the issues involved. I just wish it didn't have
compatibility issues with "normal" mode and we didn't have to have this whole
conversation.-------------------------------------73 de
Bob2_______________________________________________VHFcontesting mailing
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