Re: [amsat-bb] HF DIGITAL SSTV on SATELLITE'S....

["laura halliday" <marsgal42@xxxxxxxxxxx>]

>    There is a new DIGITAL sstv going around that looks very good for 
>sending
>pictures. The pic's are near perfect copies and the time to send them is
>short compared to
>Scottie one or martin one.
>
>    Now we ham's have all ways been some of the first to invent or try NEW
>things with radio,, I remember when some one sent a ROBOT sstv mode over a
>satellite and it
>worked...
>
>      SO who will be the first to send this new DIGITAL
>sstv over one of the satellite's.
>
>       I think testing should start soon BUT I also know
>a LOT of you will HATE the idea.
>(a whole bunch of unnecessarily-quoted material deleted)

A typical SSTV-quality signal is at most a 10k JPG image,
and takes very little time to transmit by just about any means
you wish. At school I had no difficulty sending much larger
images, particularly over KO-23 (measuring upload and
download capacity, y'know...). I got lots in return. The
chap in Tahiti took particularly neat pictures. :-)

Like all digital systems, when it works, it works perfectly. But
it doesn't degrade gracefully: the threshold between perfect
copy (albeit possibly with the decoder working very hard) and
no copy at all is very small. Graceful degradation can be
an important requirement.

For satellite operation I'd steal one of NASA's tricks: PSK
with a bit of residual carrier so you can track the Doppler.

Laura Halliday VE7LDH     "Que les nuages soient notre
Grid: CN89lg                    pied a terre..."
ICBM: 49 16.57 N 123 0.24 W        - Hospital/Shafte

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