[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Re: Discovery Project: Which Mission Next?

on 9/5/00 2:00 AM, Howard Long at howard@howardlong.com wrote:

> 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.

With anything greater than a 9600 baud modem, I believe you need to modify
the radio.  Anyhow, why limit to 28.8?  UO-36 is already got a 38.4K (or
whatever) downlink.  And P3D will have higher speeds still.  This could be a
good way to encourage high speed data.
> 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.

UGH!  Nothing is worse than chunky video.  People would find it a novelty
for a bit, play with it and then get tired of it.
> 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.

Agreed.  You need a full duplex data stream.  We would need a completely new
bird in order to do this (and some new radios):

1.) High Earth Orbit (just not enough time for video sharing on a LEO)
2.) Dedicated to high speed data
3.) Linear transponder based (more than one bloomin' channel!)
4.) Uses Microwave bands (preferably 10 GHz and up) - at 10 GHz, we in the
US have a 500 MHz allocation!  That's a LOT of high speed channels (no, we
wouldn't use the WHOLE band!).

So with P3D still not in orbit yet, perhaps we have the next satellite
concept being born!  :-)



Jon Ogden
NA9D (ex: KE9NA)



"A life lived in fear is a life half lived."

Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org