[amsat-bb] Re: Redundant geostaionary birds?

[Bruce Bostwick]

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  
full duplex!)

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
> worry.
>
> 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