[aprssig] Suggestion for APRS over Satellite

Dave Baxter dave at emv.co.uk
Wed Apr 23 03:58:21 EDT 2008

Bottom posted for once, scroll down to see...

> -----Original Message-----
> From: Stephen H. Smith [mailto:wa8lmf2 at aol.com] 
> Subject: Re: [aprssig] Suggestion for APRS over Satellite
> Hans Johnson wrote:
> > Hi All,
> >
> > I've been toying around with the idea of building some 
> equipment for 
> > extreme remote telemetry stuff to be done over satellite.  
> (Similar to 
> > Bob's project in Mongolia).
> >
> > Anyhow, one of the things that would be extremely useful is if the 
> > satellite could (occasionally) include its current orbital 
> data in the 
> > beacon packet, something like a condensed version of the Two Line 
> > Element and a CRC.  Using this information, it could then 
> power down 
> > the radio until the next useful satellite pass.  This would 
> > drastically reduce the power requirements for a remote site.  Also, 
> > things like asatlogger and what not could use the information to 
> > update their pass predictions automatically.
> >
> Won't the remote device then need to have fairly hefty 
> computing power to crunch the orbital elements into a useful 
> AOS/LOS prediction for the particular location the device is 
> located at?  
> I would guess that the power consumption of a controller with 
> enough horsepower to do this would exceed the total power 
> consumption of just having a much simpler dumber device power 
> up the radio for a few seconds every 5 or 10 mins if the 
> transmit bursts are really short. 
> Not to mention you will also need to power a receiver that 
> won't be needed with a "dumber" device, and a real-time clock 
> to wake up the 
> controller/transmitter at the appropriate times.    
> --
> Stephen H. Smith    wa8lmf (at) aol.com
> EchoLink Node:      14400    [Think bottom of the 2M band]
> Home Page:          http://wa8lmf.com  --OR--   http://wa8lmf.net

I'd sort of expect it not to be a CPU horsepower problem, after all,
it'd have the best part of 60 minutes (plus) to calculate the next AOS
based on the last received partial Kepler element set.  It's not as if
it needs to track the things in real time....

Heck, with a little (lot) of software inginuity, and an accurate clock
etc, the thing could figure out the AOS/LOS pattern over a period of
time all by itself...  Couldn't it?   After all, that's how many of us
used to use the early Oscar's before we all got computerised....   Well
within the realms of a low power CMOS CPU I'd have thought...

With that sort of functionality, you could "just drop" a satelite APRS
sensor pack, just about anywhere, and after a day or three, it'd
synchronise itself with whatever satelites it was initialy told about.

Just an idea...

Dave G0WBX.
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