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

Greg D. ko6th_greg at hotmail.com
Sat Sep 23 13:11:20 PDT 2006

So, interference in the "safety for life" band is of interest to the 
government, and lots of testing, backups, and certification will be required 
to use it.  Interference in the "commercial" band is of interest to 
Galileo's bottom line ($$), and they will be motivated ($$, again) to invest 
the least for the best payback.  My worry is that it may appear cheaper to 
them to try to ban all other uses of those frequencies, than to invest in 
the engineering design and end-user hardware components to prevent that 
service from going down.  Loss of life due to interference cannot be 
tolerated, of course, but to see what motivates action, follow the money.

Greg  KO6TH

----Original Message Follows----
From: Bruce Rahn <brahn at woh.rr.com>
Reply-To: brahn at woh.rr.com
To: "John B. Stephensen" <kd6ozh at comcast.net>
CC: amsat bb <amsat-bb at amsat.org>
Subject: [amsat-bb] Re: Galileo interference on L band
Date: Thu, 21 Sep 2006 14:28:21 -0400

John B. Stephensen wrote:
 > High-accuracy receivers use multiple downlink frequencies to compensate 
 > errors, such as those induced by the ionosphere. There are probably 3
 > downlink frequencies in case 1 fails.
 > 73,
 > John
 > ----- Original Message -----
 > From: <sco at sco-inc.com>
 > To: "amsat bb" <amsat-bb at amsat.org>
 > Sent: Thursday, September 21, 2006 16:54 UTC
 > Subject: [amsat-bb] Re: Galileo interference on L band
 >> I understand this argument. BUT what i do not understand is the idea
 >> that an airliner would only be receiving one of the three bands that
 >> Galileo is saying that it intends to use for GPS. The L band is in
 >> just one of those three bands that the airplane would be receiving.
 >> Would the system not require the receiver to take data from the best
 >> signal? Could we not ask the FAA to require any airborne receiver
 >> that it certify must receive all three bands and switch bands if it
 >> receives any interference?
 >> As a practical matter G GPS is not now in orbit, it would take years
 >> before it could be funded, launched and be operational. Then it would
 >> take the FAA probably another 10 years before they would certify it
 >> for use.  I see 10-15-20 years before Galileo might be a problem to 
 >> Why not fly Eagle with a backup L/S linear and use C/X for the
 >> digital transponder?

This debate grows more interesting with time.

Current publicly available Galileo documentation indicates that "Safety
of Life" services will be provided on  E5a/E5b (1164 to 1215 MHz)
downlink and the E2/L1/E1 (1559 to 1591 MHz)  downlink.  The E6 (1260 to
1300 MHz) downlink is designated for 'commercial services' and not the
aviation.  Thus, I am VERY curious why the interference to aircraft
navigation receivers is constantly brought up in this discussion as it
appears a non-player.

For all but the most precise needs, dual frequency capabilities will
eliminate the 1st order ionospheric errors leaving only the 2nd and 3rd
order terms which are on the centimeter level.  Thus I don't see the
need for aircraft navigation systems to employ 'tri-frequency' receivers.

What am I missing here?

Bruce Rahn

Wisdom has two parts:
1.  having a lot to say; and
2.  not saying it!

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