Bill,
I've already written a requirements document for the L receiver. It may end up being a U receiver (see EaglePedia for description and schematics) modified for different first LO and RF frequencies. It's a secondary uplink for the linear transponder, but can't be the primary uplink for the digital transponder.
73,
John KD6OZH
----- Original Message ----- From: "Bob McGwier" [email protected] To: "Bill Ress" [email protected] Cc: [email protected] Sent: Wednesday, September 20, 2006 18:21 UTC Subject: [amsat-bb] Re: Why do the amsats get more and more complex?
Bill Ress wrote:
Hi Rick,
I've been critical of the "no L-Band" decision and your recent comments don't lessen that critique.
Your last posting said "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."
What concrete evidence is available that substantiates your claim? Perhaps "real" data could convince me and others that the decision is based on fact and not a paranoia about what could happen. Everything I've heard to date from AMSAT is anecdotal, opinionated and based on what you just said - FEAR.
What will happen if the Galileo goes up is that no European airport will allow a commercial jetliner to land without the Galileo system. This will inevitably lead to this basic system being in world wide use for navigational purposes. The Near/Far difference between your emission of billions of times as much power (so far as the aircraft receiver is concerned) as that to be received by the aircraft from the satellite will inevitably lead to collapse of the front end. The receiver manufacturers will not want to build high quality, expensive front ends to filter out powerful emissions that could bring an airplane down. They will choose the path of "clean the bums out" and they will win. The Europeans no longer wish to maintain the VOR sites and their contention is that Galileo will be less expensive in the long run. There are indeed some who argue the upfront cost will be too large for the Europeans to actually come up with but until they announce this one must assume they will go forward.
So your idea is that we should spend $10,000,000 of donated money on the back of prayer that Galileo will not force us off our band when we KNOW it will be viewed as a safety of life service and that we will overload the front ends of the receiver in the (admittedly very rare) cases where the airplanes are in our emitter beams? No one can be that naive to believe that even the slightest possibility of interference will be allowed.
To the contrary, the "fact" is that Galileo's own web site states (which I have referenced here already) the reality of having to work in an interference environment (i.e. ground ATC radar's and harmonics from TV transmitters just to name of few) and has already started a two year study program to evaluate appropriate design considerations.
We cannot use L band for the advanced communications package anyway because we do not want to increase the antenna size for the ground user. We want to accomodate CC&R restricted users with a 60cm (2 foot) dish. The L band feed required, being dual band with C band (say) makes this infeasible.
So the argument is whether or not to design an L band receiver for the linear transponder. I have asked John Stephensen to do just exactly that. I asked him to do this a few months ago and he has taken up the challenge. I don't understand what the argument is about.
I have been unable to find ANY reference to any governmental agency making plans to eliminate the L-Band Amateur allocation in view of Galileo. Do you have evidence to the contrary?
Another "fact" is that the P3E team, rather than "abandoning" the allocation, has an "engineering" approach to mitigate the potential for interference by selecting a L-Band frequency which puts the signal in a Galileo signal null (already pointed out by others here).
Here is a fact you have not taken into account. The advanced communications package needs 10 MHz not a few tens of kHz but I have already discussed why L band is not usable for the system (ground and space) we are attempting to accomodate. That has nothing to do with Galileo or the loss of L band. In fact, if we can fit the antennas on the spacecraft, I see no reason we shouldn't include an L band receiver and we should drop it into the Galileo null. The issue will be coordination with our AMSAT-DL friends and partners to mitigate interference issues. These should be rare indeed if we achieve our target orbit for Eagle and they achieve their target orbit for P3E. The birds will be many degrees apart almost always when L band will be appropriate.
This debate could be put to rest if you could present us with "facts" and not the "lets get out of the kitchen 'cause we may not be able to stand the heat" argument I've seen so far.
Ready to be convinced...
Bill - N6GHz AMSAT #21049
73's Bob N4HY
-- Robert W. McGwier, Ph.D. Center for Communications Research 805 Bunn Drive Princeton, NJ 08540 (609)-924-4600 (sig required by employer)
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