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

John B. Stephensen kd6ozh at comcast.net
Wed Sep 20 11:56:55 PDT 2006


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 



----- Original Message ----- 
From: "Bob McGwier" <n4hy at idaccr.org>
To: "Bill Ress" <bill at hsmicrowave.com>
Cc: <amsat-bb at amsat.org>
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 
>>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 - 
> 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 
>>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 
>>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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