[amsat-bb] Re: Why do the amsats get more and more complex?
John B. Stephensen
kd6ozh at comcast.net
Wed Sep 20 11:05:36 PDT 2006
Unfortunately, the Gaileo downlink covers 1258-1299 MHz, the first satellite
has been lanched and the satellites in the constellation will be on over the
entire world. Our uplink antennas have sidelobes that are 10-20 dB down, so
a 1 kW EIRP SSB uplink results in 10-100 W radiated towards terrestrial
receivers. A 256 kbps uplink would require 16 kW EIRP and be 0.5-1 MHz wide.
P3E has a second L receiver tuned to a null in the Galileo signal (there is
only one null in the 1260-1270 MHz band) but no one knows if this will help.
SSB users can move to the U uplink if L is a problem. However, this only
works for narrowband signals. A wideband uplink won't fit in the null and
can't move down in frequency.
----- Original Message -----
From: <sco at sco-inc.com>
To: <amsat-bb at amsat.org>
Sent: Wednesday, September 20, 2006 16:16 UTC
Subject: [amsat-bb] Re: Why do the amsats get more and more complex?
> Galileo (if it is ever built and launched and worked) would just be
> over Europe, right? That would leave the rest of the world the
> ability to use our L band uplink, right? If we hams are using a dish
> pointed at the sky with a narrow bandwidth how is that going to
> interfere with ground receivers some distance from us? We would be
> smart enough to not have the Eagle uplink on the same freq, right?
> And we would design Eagle such that we could (from ground control)
> move the Eagle receive freq away from any potential conflict with
> Galileo, right? And Eagle would be in orbit and operational long
> before Galileo, right? And Galileo receivers on the ground will have
> the ability to cut out any possible interference from us, right?
> Seems to me that we are planning to give up the L band (as an uplink)
> based on a lot of bad assumptions.
> Les W4SCO
>>The answer is in two parts. First, an L-band ground antenna would be too
>>large to disguise as a TVRO dish. Second, there is fear that over the
>>lifetime of Eagle that L-band could become unavailable, particularly in
>>Europe, if the Galileo system is deployed. Galileo would be a primary
>>service and Ham transmissions would likely interfere with low cost
>>I don't wish to debate these points. I'm just telling you the reasoning
>>went into not choosing L-band. I assure you that every possibility was
>>considered. Lists were created and discussed on each alternative.
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