[CQ-Contest] WWDIGI Contest Testing...

[Richard Ferch]

It seems to me that a lot of this discussion is missing a key point. The
problem is not what to do when you have 100% copy; the default protocol
takes care of that. It's what to do when copy is poor/intermittent/marginal:

CQ WZ1ZZZ FN31
WZ1ZZZ AA6AAA DM04
AA6AAA WZ1ZZZ R FN31
So far so good. At this point, AA6AAA sends either WZ1ZZZ AA6AAA RR73 if
his software copies the exchange, or  WZ1ZZZ AA6AAA DM04   (repeats the
call message) if it does not copy the exchange from WZ1ZZZ. All of this is
pretty much automatic.

Suppose AA6AAA sends the RR73 message. His software auto-logs the contact
and as far as he is concerned the contact has been completed. But what if
WZ1ZZZ's software does not copy that RR73 message? He doesn't know which of
the two messages AA6AAA sent. His software automatically repeats the R FN31
message (the contest exchange), and is now waiting for the RR73 from AA6AAA
before it will finish the auto-sequence and log the contact. Meanwhile
AA6AAA has already logged the contact and may have gone on and started a
new contact with someone else.

If WZ1ZZZ copies AA6AAA sending to someone else in the next time slot, he
might conclude that he just missed the RR73 and log the contact manually,
but he might instead conclude that the contact was incomplete and not log
it (especially if he is depending on auto-logging). On the other hand, if
WZ1ZZZ does not copy anything from AA6AAA in the next time slot, he has no
information on which to base a decision whether to log the contact or not,
and possibly will not log it, resulting in a NIL for AA6AAA.

Is this different from analog modes? Qualitatively, no - you can come up
with similar scenarios. But in terms of the likelihood of the undesired
outcome (one side logs the contact and the other does not), I think the
probabilities are different. In analog modes, copy is rarely all or
nothing. WZ1ZZZ can usually copy enough of AA6AAA's second message to give
him an idea whether it was the exchange or a repeat request. In FT8/FT4,
copy is all or nothing - there is no partial copy to give the operator a
clue. In analog modes, if copy is too rough to base a decision, there is
the possibility of asking AGN? For practical purposes, this doesn't really
exist in the rigidly structured FT8/FT4 sequence. I believe the end result
is likely to be more unresolved ambiguous situations, leading to more
situations where one station logs the contact but the other station does
not.

My guess is that the error rates in WWDIGI are going to be quite different
from the contests we are used to. The rates for bad call signs and bad
exchanges should be virtually zero (the software doesn't generally miscopy
call signs or exchanges, it either gets them right or not at all), but I
believe the rates for NIL contacts will be quite a lot higher than in
traditional modes. There will be a temptation to blame this on contest
newbies showing up in the new mode, but IMO there are structural reasons
for expecting high rates of NILs.

73,
Rich VE3KI