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

Tom Clark, K3IO K3IO at verizon.net
Thu Sep 21 20:51:40 PDT 2006

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 off, just so everyone can read the presentation materials that we
used during the San Diego meeting, please take a look at the EaglePedia
web site at 
Then take a look at my presentation "Frequency Considerations for Eagle"
You will see (my slide 6) that I present the arguments pro/con about why
(IMHO) L-band is at jeopardy as a long-term uplink band.

Let me add a few comments about why I'm so concerned. The reason that
the Galileo E6 (functionally the same as GPS L2, and overlaying the
amateur 1260-70 MHz uplink allocation) is important for some uses is
that it, when used in combination with the primary 1.57± GHz "L1"
frequency (which is what all your cheap hand-held GPS receivers use),
can be used to correct the ionospheric errors; the ionosphere adds
upwards of 10 meters to the pseudo-range for each GPS satellite. Because
of geometric factors (expressed quantitatively in VDOP), this can in
turn yield errors in height of up to about 30 meters. [The WAAS and
EGNOS signals provide some correction for these biases to the few meter
level, but cannot be relied on during severe ionospheric storms.]

There is a lot of factual evidence that when dual-frequency geodetic GPS
receivers (costing ~$25,000 -- hardly cheap!) have been used in
proximity to terrestrial amateur L-band stations, the GPS performance is
seriously degraded. I direct your attention to several reports on the topic:

    * Must reading -- GPS/GLONASS vs L-band digipeaters (Also see GPS
      World, Oct.2002) (warning contains numbers and equations, as well
      as uncomplimentary comments about digipeaters)
    * Amateur and Radar QRM reported at a 1999 technical meeting:
    * A tutorial that shows how interfering signals can affect a spread
      spectrum GPS rcvr (caution --  contains more
      numbers): http://www.rin.org.uk/SITE/UPLOAD/DOCUMENT/Vuln-Owen.pdf#search=%22gps%20amateur%20interference%22

Even though US amateurs may feel that Galileo is a "European only"
problem, read carefully Rick's (W2GPS) comments -- in his real life for
many years he was a VP with ARINC (the people who worry about standards
in the airline industry) and was on many FAA and ICAO committees that
decide on airline safety.

Also realize that the Europeans are absolutely determined to develop
their own GNSS (Global Navigation Satellite System) call Galileo -- in
part because they don't really trust a system that depends on the US
Military, and in part because they see a giga-Euro business opportunity
for the EC. Who knows how long it will survive, but the Russians have
their competing GLONASS system. And both the Chinese and Japanese see
that they need to enter into the GNSS race is they are to be world-class
technical competitors.

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.

73, Tom

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