[amsat-bb] Re: Why do the amsats get more and more complex?

[John B. Stephensen]

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.

73,

John
KD6OZH

----- 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
>>commercial receivers.
>>
>>I don't wish to debate these points. I'm just telling you the reasoning 
>>that
>>went into not choosing L-band. I assure you that every possibility was
>>considered. Lists were created and discussed on each alternative.
>>
>>Rick
>>W2GPS
>>AMSAT LM2232
>
>
>
> _______________________________________________
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb