[amsat-bb] Re: Redundant geostaionary birds?
lihan161051 at sbcglobal.net
Sun Jan 28 14:26:15 PST 2007
I don't know of any GEO sats that have uplinks within amateur bands.
The ones I know about all seem to be either C-band or Ku-band, and
have uplinks in the 5.9 GHz (C-band) or 14 GHz (Ku-band) ranges.
While it's quite possible that the sats are accessible from anywhere
on earth that's in their footprint, you'd need an appropriate license
to transmit on the correct uplink frequencies to get into the
transponders .. at least legally ..
GEO sats are also moved to a junk orbit when they run out of
stationkeeping propellant, so they're no longer geostationary and
drift quite a bit from day to day. You wouldn't need much steering
on a dish to track one, and wouldn't need more than one axis as far
as I know, but you would definitely need to maintain good keps on the
bird to be able to keep it in the middle of your main lobe. And you
would need at least 50-100 watts of uplink to get a usable downlink
signal (as i recall, a full-bandwidth analog TV signal took about 600
watts to get to GE-2 last time I watched an uplink in progress, I
know some folks who can tell you far more than I could about this..)
and you'd need a feed that could completely reject the uplink to keep
from desensing your downlink receiver. (You definitely want to do it
Could be entertaining, if the legalities could be worked out, but I
don't know if any of the dead sats can be accessed using ham freqs,
or what the consequences would be of a ham downlink coming down on
commercial frequencies. (Bear in mind that if the sat is too close
to the location of an *active* sat, and transmitting, its downlink
might interfere with the downlink of the one it's passing behind, or
you might get into the uplink of the active bird, or both. Could be
a real mess.) In short, probably impractical for North America and
Europe/Africa. More remote parts of the world could have some fun
with this though ..
(Lots of additional useful info available at http://www.lyngsat.com/)
On Jan 28, 2007, at 10:54 AM, Andythomas wrote:
> Then I fell to wondering:
> whether we in the amateur satellite service could not use both the
> up and
> down links on these redundant geostationary birds?
> I don't know the exaxct frequencies but there may be one out there
> that has
> frequencies we share (or at least the uplink). After all we have
> years of
> experience of chasing staellites which are not exactly where they
> should be
> in the sky and so the "wandering geostationary" satellite shouldn't
> be a
> I think each transponder channel is 27 MHz wide??
"No, I'm disagreeing with you. That doesn't mean I'm not listening to
you or understanding what you're saying. I'm doing all three at the
same time." -- Toby Ziegler
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