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@sco-inc.com To: amsat-bb@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
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