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Re: Re: Discovery Project: Which Mission Next?



Bob,

1 Pic/sec sounds about right.

I've been pondering digital video for a few weeks myself, so my thoughts may
be of some interest. There's two differences to my train of thought though.
I wanted to try the option of (semi) motion video and normal IF bandwidths.

Anyway, here's my thoughts...

I wonder if there's any way of extracting the compressed digital output
from, say, NetMeeting, and modulating that? A few years ago I fiddled with
programming Video for Windows (which is the Windows API that NetMeeting
uses), but I remember that it's quite a closed system, and that getting hold
of the inputs or outputs of the Video Codecs directly wasn't possible (or at
least I couldn't work out how to do it).

Is there a reason why we can't use old 28.8 modem technology somehow? These
use a low bandwidth (3kHz?) analog system, so there'd be no need to fiddle
the TX/RX IF bandwidths. I guess one fundamental difficulty might be that
phone lines are less noisy than the sorts of weak signal RF we're talking
about. My modem knowledge isn't very good, although I'm sure some on the
reflector would be able to explain.

I have tried NetMeeting in the past over a cellular 9600 link and it does
work (slowly), including choppy audio and rather chunky video. Maybe even
using a 9600 radio modem we could get something to work, if I could hook
NetMeeting or something similar to the modem.

I might try this directly in the following way. The SV2AGW Windows IP packet
driver at 9600 could be the glue between NetMeeting and the radio. I have a
feeling that being half duplex things might not be very good. I also don't
think that IP or any packet style system would be the optimum medium for our
requirements. The amount of lost bandwidth as stations switch from transmit
to receive is quite high. A point to point connection at full duplex would
improve things. Not to good for a satellite, though, with single uplink and
downlink frequencies. Maybe you'd want to limit the information to one
picture and a tiny bit of audio.

But if it works at 9600, you could make yourself quite a nice little station
with a TH-D7EmkII and one of those little Sony Vaios with the camera.

All you'd need then is a satellite to cooperate.

Mmm... Got me thinking (or was that dreaming).

73 Howard G6LVB

----- Original Message -----
From: Bob Bruninga <bruninga@nadn.navy.mil>
To: <k6ccc@AMSAT.Org>
Cc: amsat-bb@amsat.org <amsat-bb@AMSAT.Org>
Sent: Tuesday, September 05, 2000 4:11 AM
Subject: Re: [amsat-bb] Re: Discovery Project: Which Mission Next?


> As everyone points out, the bandwidth of FSTV is horrendous and takes at
> least 24 dB greater than FM for any satellite link, probably the best
> compromise would be the FAST-FM mode now used between kenwood radios an
> the VC-H1 SSTV converter.  I think this takes only 15 seconds for a pretty
> good image.  But still, that is awfully slow.
>
> But on a LEO bird, what value is anything more than that?  Everyone in the
> whole USA would have to share just 15 minutes, and we have demosntrated
> that that is difficult to do on LEO's
>
> What I think we need is something like about a 1 second frame rate.  This
> would only take 12 dB more than FM and about 250 KHz instead of the 6 MHz
> for FSTV..  But rather than inventing another wheel, I suspect the mor
> universal approach will be just to have a high data rate digital
> transponsder, and then JPIG images can be exchanged just as easliy...  ANd
> with the possible compression, this will be far more effecient thatn
> either FSTV or FAST-FM SSTV....
>
> In any case, what would be a good target?  1 Image a second?
>
> de WB4APR, Bob
>
>
> ----
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