Re: Missing Segments

David J Taylor GM8ARV 🏴󠁧󠁢󠁳󠁣󠁴󠁿 🇪🇺

--- In, "David Strickland" <David@s...> wrote:
Further to my post yesterday at 0830 I missed seg. 5 from
chans. 6,8,9,10,11 and seg.15 from chan 12. The interesting thing
here is channel 9 as it was amoung the groups of channels
as well! I would think that if the files sent were in groups of
channels then this is an unexpected result. Signal quality is a
steady 70-71% with SNR 10.8 a 88cm dish weather is good and dish
very rigid mounted. Even in a strong gale little signal variation
occurs. The dropped segments look to me like a software problem.
I am trying to get a better understanding of this. I made a plot of
the percent loss of segments versus channel number, expecting to
find that the channel where the files which were larger would have a
greater segment loss, and there was less likelhood of getting a
complete file. Similarly I had expected that LRIT data would be
more robust than HRIT data, but this also not seem to be the case
when the loss was at its worst. It suggested that some file
grouping was perhaps spreading the loss more equally across all

Guesswork, I'm afraid.

I don't expect any file grouping to be constant, by the way. I
(again) guess that there is a data stream and that all files of a
certain priority will be packaged for transmission in some sort
of "best fit to available packets" fashion. I don't know if the
IMPF software processes files in a strict channel order, or if there
are parallel processing tasks so the channel order for a particular
segment is random. I should study the log files, shouldn't I?

The Sky star card is in the computer in the garage!!
.. and so perhaps is subject to a larger temperature variation than
a "domestic" computer might expect to encounter?


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