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

Bruce Rahn brahn at woh.rr.com
Thu Sep 21 11:28:21 PDT 2006

John B. Stephensen wrote:
> High-accuracy receivers use multiple downlink frequencies to compensate for 
> 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 hams.
>> 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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