[amsat-bb] Re: Galileo interference on L band

Bill Ress bill at hsmicrowave.com
Thu Sep 21 23:54:32 PDT 2006

Hi Tom,

You stated:

"Sorry -- I've been away from home on business while the latest flack
occurred under the general topic heading "Galileo interference on L band"."

First, I would hope we could characterize the past proceedings on the -bb as
a useful debate rather than "flack."

That said, I do appreciate your links on interference which I have read
previously but they can be useful to others following this discussion.

But perhaps my conclusions, after reading the links, might differ from
yours. But, I think we can agree, as I have stated before, that a potential
for interference "could" possibly exist, albeit, at some future time.

The key issue here for us the use of the Amateur satellite L-Band 1260 to
1270 Mhz.

The articles you reference deal primarily with interference to G2 GLONOSS
which operates at 1240 to 1256. One of the interfering signals the articles
point out are German Digipeaters operating in the (authorized) frequency
range of 1240 to 1242 Mhz (the low end of the G2 band).

That material was published in 1999. While I don't have the answer, maybe
you do, the question to ask is: in the seven intervening years has there
been any GLONOSS or GPS "public safety" issues resulting from the Digipeater
operations, and have these Digipeaters since been taken off the air by the
regulatory agencies?

I believe the articles also hit heavy on the ATC radar interference in
Germany (and likely elsewhere). Do we know if any of the ATC radars have
moved in frequency?

The articles also point out interference deficiencies in several of the
receivers tested and alludes to ways of mitigating their deficiencies. I'm
sure that over the past seven years receiver improvements have been made.

You also said:

"We the Eagle technical team, have never said that L-band won't work NOW
or 5 years from now. But our vision for Eagle is that when the first one
flies 4-5 years from now, we want it to be a useful resource for at
least a 10 year lifetime. We are very concerned about making a several
million dollar (after you count the volunteer builder's blood, sweat &
tears) investment only to have it blown away right after launch by the
GNSS cartels just because we picked L-band to be anything like a
"primary" uplink."

Yes - those are admirable desires but we can't engineer for "unknown" future
events. It just bogs us down with worry that we might not make the right
"guess." Instead, as I stated before, base decisions on the engineering
facts as we know them today (available technology, size, power, space,
resources, user needs, etc.) and let the future bring on whatever it has in
store for us.

If you can make arguments that L-Band won't work because of system
engineering constraints or the mission objectives we have before us today -
I can live with that. But lets take this Galileo "cloud" off the decision

I don't think many future AMSAT communicators will fault you for not being
able to predict the future.

Regards...Bill - N6GHz

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