Re: [amsat-bb] Re: Discovery Project: Which Mission Next?

[tlang@xxxxxxxxxxxxxxxxxxxx (Tony Langdon)]

Hello Howard!

05 Sep 00 08:00, you wrote to All:

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

Probably not at the data level, without a heap of hack^H^H^H^Hcoding. :-)

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

Other problems include training, which takes several seconds for modems (listen
next time you dial up).

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

I'd want to see something a bit faster than 9600, I think.

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

Extracting data at the IP level would be relatively simple.  However, running
TCP/IP between random stations across the bird might be tricky, unless you
define a large range of IPs (maybe experiment with 10.x.x.x) as a large
subnet...  Still, fun to play with. :)

Tony, VK3JED

.. We might be nerds, but at least we're off the streets.
--
|Fidonet:  Tony Langdon 3:633/284.18
|Internet: tlang@freeway.apana.org.au
|
| Standard disclaimer: The views of this user are strictly his own.


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