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Re: commutating antennas (was snip)



>And I guess that pretty well defines the two sides which occupy much of the 
>conversation that goes on on this BB.  There are those that are looking 
>mainly at optimum engineering solutions and those that want to try to factor 
>in less well defined political/people requirements.

Why do you think these are two "sides" here, somehow in conflict?  Do
you think that by calling for an "optimum engineering solution", I'm
proposing something counter to what most of the members want?

I think that if you carefully re-read what I said, and what I've said
on other occasions here and at the annual meetings, you'll see that I
am indeed advocating a systems approach to the problem of providing
high quality amateur satellite communications to as many hams as
possible at the lowest possible total system cost.

A communication satellite system consists of two segments: the earth
segment (ground user stations) and the space segment (the satellite
and its control stations). So a "system approach" means that you look
at both and make tradeoffs between them that maximize overall
performance and minimize total cost.

So what does a systems approach say about AMSAT's current practices?

1. The use of inefficient analog modulation methods (CW, SSB & FM)
   instead of modern digital methods results in substantially higher
   system costs (especially on the spacecraft), substantially larger
   ground and/or spacecraft antennas, substantially poorer
   communications quality, and substantially lower capacity. They may
   rule out certain promising spacecraft designs, e.g., the "switched
   antenna array" we've been discussing, or an onboard digital
   regenerator like RUDAK.

2. The use of low frequency bands (especially 2m) where bandwidth is
   severely limited and artificial and natural noise levels are high
   also implies larger antennas, substantially higher system costs and
   substantially lower system capacity and quality.
   
3. A requirement for large antennas keeps away many prospective
   satellite operators. Sure, you can work an "easysat" with a small
   hand-held antenna. But the mere fact that they are *called*
   "easysats" shows that we have a real problem with the satellites
   that *aren't* "easysats".


The conclusions are obvious. If AMSAT is ever to significantly improve
the quality of its satellite systems, reduce its costs, and attract
more users, it has *no choice* but to adopt more efficient digital
modulation schemes and move up to the microwave bands. This isn't just
an optimum engineering solution. It's what we *must* do to survive.

Yes, this requires new ground station equipment that we don't have
now. But why is that so terrible? AMSAT appears poised to spend
several million dollars to design, build and launch a major new
satellite or two. If so, shouldn't AMSAT and its members also be
willing to spend some small fraction of that amount to design, build
and manufacture new ground station equipment that could
*substantially* reduce the cost of these new satellites, increase the
quality of the service they provide, and permit many hams currently
limited by space restrictions or CC&Rs to join AMSAT and use the
satellites?

Just *who* is being elitist here, anyway?

Phil


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