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Re: Amateur radio module on commercial Geo Sat?



Most operators should be able to find their position within a few kilometers
even using a map. Once the users location is known, the tracking portion of
the software should be able to compute burst time offset from the calculated
slant range, using ephemeris data, close enough to put the user into a extra
wide "ranging slot". The user could then synchronize to a network reference
that could be generated by a designated ground station or on board the
satellite. Once a user has ranged, he would be allowed to join the network.
Doing it this way is sort of a compromise. It would not be as elegant,
accurate or automatic as using a GPS receiver, but it would allow the
process to be built into the access protocol software and not require the
purchase of a GPS receiver and interfacing external hardware, hopefully
making it easier to get up and running.....maybe.

I actually had success using a technique similar to this for deploying
portable Hughes PES TDM/TDMA VSATs on Ku band.

Just thinking out loud...
de Howie, AB2S

----- Original Message -----
From: "Phil Karn" <karn@ka9q.net>
To: <tlang@freeway.apana.org.au>
Cc: <amsat-bb@AMSAT.Org>
Sent: Wednesday, December 20, 2000 11:23 AM
Subject: Re: [amsat-bb] Amateur radio module on commercial Geo Sat?


> >So, basically a case of using GPS to measure positional differences and
time
> >delays?  These days, quite feasible, given the lowish cost of surplus GPS
> >engines that can be obtained from time to time.
>
> Right. It was tempting to make a GPS receiver an integral part of such
> a station, perhaps as a timing reference for the TDMA uplink
> transmissions. My main reservation was the potential for interference
> from a co-located L-band uplink, as many commercial GPS receivers have
> poor front-end selectivity. A cavity filter on the GPS front end fixes
> the problem, but that's extra cost. Hence it would be best to rely on
> the GPS only working often enough to give you user position and time
> accurate enough to compute slant range within a few tens of km.
>
> Phil
>
> ----
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