[amsat-bb] Re: All Satellites (Alan P. Biddle)
John B. Stephensen
kd6ozh at comcast.net
Sun Sep 27 08:51:43 PDT 2009
The 1200 bps Pacsats used an uncoded BPSK downlink on 70 cm and worked fine
with 1/4-wavelength vertical antenna on the ground. As I remember, they only
generated 1 watt of RF. A 2-meter downlink using an error correcting code
would give 4 times the data rate with the same power. Digital voice now fits
in 1200 bps so you could support APRS plus multiple voice channels.
----- Original Message -----
From: "Robert Bruninga" <bruninga at usna.edu>
To: <amsat-bb at amsat.org>
Sent: Sunday, September 27, 2009 14:42 UTC
Subject: [amsat-bb] Re: All Satellites (Alan P. Biddle)
>>> And wouldn?t it be a hoot if [these cubesats]
>>> could put their RX/TX into a bent-pipe packet
>>> mode, and then we would have amateur radio
>>> global hand-held text messaging satellite system...
>>> Using some of the 2-way very small micro APRS
>>> packet systems, a 2 to 5 Watt transponder will
>>> easily fit... in a small cubesat.
>>> See www.aprs.org/cubesat-comms.html
>> If you could have maybe five or six cubesats
>> with an FM transponder... [with] a good 15-minute pass
>> every hour... would work wonders for getting people
>> interested in satellites again. ... [with a]
>> dual-band HT and a homebrew Arrow clone
> The beauty of the APRS packet text-messaging relay cubesat is
> that it can have a 10 times higher power transmitter compared to
> an FM voice transponder for the same average power budget. This
> makes it workable on an HT with just a whip antenna, instead of
> needing a handheld beam. Plus, each message takes one second
> instead of 15 for each QSO.
> So that is why I prefer handheld packet text messaging as a
> cubesat mission. Ten times the downlink power budget and 15
> times the number of contacts per pass.
> AO51 downlink could be 10 times as strong if the transmitter
> would just drop when not in use...
> Bob, WB4APR
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