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

Bob McGwier n4hy at idaccr.org
Wed Sep 20 11:21:00 PDT 2006

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 

>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

Robert W. McGwier, Ph.D.
Center for Communications Research
805 Bunn Drive
Princeton, NJ 08540
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