Hi Dwayne,
I discussed these issues at some length with Bob, KA1GT, some 1.5 years
ago. Here are the relevant details.
Sure, we could make a version of Q65-15A that can decode after normal
EME delays. It would not be a very good fit for the channel, however.
This is because the duration of a Q65 transmission is 12.8 s, and the
transmission starts at t = 0.5 s into the 15-second sequence. Add a 2.7
s EME delay, and you're already 1 second into the next sequence -- even
without any clock errors.
You could make the Tx duration smaller, say 10 s. Then, if the
transmission starts at t=0.5 s and there's a 2.7 s EME delay, reception
would be complete at t=10.5 + 2.7 = 13.2 s, and (if clocks were spot on)
the decoder would have 1.8 s to do its thing. Even this is not really
enough, because clocks are not always "spot on". Moreover, you would
lose an additional 10*log(12.8/10.0) = 1 dB of sensitivity. WSJT moders
do a lot to gain every 0.1 dB of sensitivity, so we certainly don't want
to to that!
Fifteen-second sequences are not an efficient choice for a path with
delays as large as 2.7 s. If there were many times more EME activity
than at present, so that very fast QSOs were desirable in contests, and
if nearly everybody had many dB's to spare on the EME path, something
like Q65-15A might be desirable. As things stand, our advice is to use
Q65-30B for EME on 1296 MHz.
-- 73, Joe, K1JT
On 1/22/2024 3:36 PM, Dwayne Sinclair wrote:
Thanks Joe for QSO and the confirmation that Q65-15A is not to be used for EME.
Our “bad” in that in our circles we may have been referring to it as broken.
The attached article details some of the testing that has occurred to date in
an attempt to work with what we have.
I guess the EME community (including me) are looking for a faster QSO where
conditions and equipment support it?
Regards Dwayne AB6A
On Jan 22, 2024, at 11:54 AM, Joe Taylor <j...@princeton.edu> wrote:
Hi Dwayne,
Thanks for the QSO with W2ZQ, last evening.
Who is saying Q65-15A is broken, and why?
Are you (or they?) talking about EME? If so, are you aware that the Q65-15x
submodes are not supposed to work for EME. The 2.5 s EME delay is too large.
-- 73, Joe, K1JT
On 1/22/2024 2:04 PM, Dwayne Sinclair via wsjt-devel wrote:
There have been ongoing reports from various operators best summarized in the
post attached that Q65-15A is “broken”. What is current consensus on this and
if it is broken, is there any plans to address the issues?
Q65-15A Part II Testing and Sensitivity Bob Atkins - KA1GT
<https://www.bobatkins.com/radio/Q65-15_eme_II.html>
bobatkins.com <https://www.bobatkins.com/radio/Q65-15_eme_II.html>
favicon.ico <https://www.bobatkins.com/radio/Q65-15_eme_II.html>
<https://www.bobatkins.com/radio/Q65-15_eme_II.html>
Regards Dwayne AB6A
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