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RE: P3D information



> Yes. Globalstar phones operate on L and S band with nondirectional
> user antennas. So there's an existence proof, albeit a non-amateur
> one that uses LEO satellites.

Indeed, there have been a few phone systems which work with similar
handsets.

> When designing a downlink, there's always a tradeoff between satellite
> power, satellite antenna gain and earth station antenna gain. Omni
> ground antennas are quite workable if the satellite runs high power,
> has a big antenna or is at low altitude. The key is to use the most
> efficient modulation and coding available, which mandates digital.

This makes sense...  Hmm, at this rate, I may be doing tram mobile routinely
on digital systems, instead of having to push technology, operating skills
and planning to their limits to make it work! :-)

> As I pointed out in my original note, you can use an omni antenna on
> 70cm to receive the RUDAK high speed link (67 kb/s) from
> apogee. That's a link that just won't work with analog. Of course, we

Impressive!  This, I'd like to see.  Now all we need are the right radios...


> could support even higher data rates with directional antennas and
> higher frequencies, but I'll be the first to agree that our prime
> concern must be to reduce the size, cost and hassle factor of the
> minimum usable amateur satellite ground antenna. That's *the* key to
> growing AMSAT beyond its present small niche.

I agree.  The biggest issues I see for satellite operations becoming more
"mainstream" are:

1.  Antenna size limitations.  We have proven for LEOs, we can keep antennas
down to a portable size, but this isn't the case for higher altitude birds
like AO-10 or P3D (but Mode L/S should improve things there).  Fixed
directional arrays require expensive rotors and a more mechanically complex
mounting, which may not be suitable for many hams (can anyone say "rented
house", "apartment" or "unit")?

2.  Operator skill levels - Factors such as Doppler correction can be an
issue for some.  Some of these can be overcome by computer control, at a
price.  For the rest of us, we have the choice of either learning the
skills, or forgetting the idea altogether.

3.  Available equipment - This will be a big issue in the early stages of
digital adoption as well, but existing all mode gear tends to be base
station oriented, not ideal for those of us unable to put up suitable fixed
antennas.

A cheap, portable digital system could be interesting to play with...
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