[time-nuts] WAAS.....
Brian Lloyd
brian at lloyd.com
Thu Jan 9 18:58:45 UTC 2014
On Thu, Jan 9, 2014 at 12:21 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
>
> brian at lloyd.com said:
> > navigation system that is going up. For that matter, is anyone running
> one
> > of the new multi-system receivers? I notice that Garmin is selling them
> as a
> > matter of course now. The prevalence of jamming might be the reason why.
>
> Aren't the alternatives using frequencies that are very close? Close
> enough
> so one the same receiver can pick up all the satellites. How much wider is
> the total bandwidth? Does the filter on a typical L1 antenna reject, or
> maybe just weaken, any of the other systems?
>
GLONASS works on 1602.0 MHz (+/- ~4MHz). GPS works on 1575.42 MHz. There is
only about 20 MHz difference at 1.6GHz so it is entirely possible that a
wideband (noise-based) jammer would take out both, but be quite limited in
range. A narrow-band jammer would probably take out GPS but GLONASS uses
FDMA and separates each satellite in frequency by 0.5625 MHz. That means
that a narrow-band jammer might get one, two, or three birds but probably
not all of them.
It does seem to me that a combined GPS/GLONASS receiver is going to be more
resistant to jamming than a GPS-only receiver.
And I make no claims to being an expert. I am just mostly thinking aloud
here.
--
Brian Lloyd, WB6RQN/J79BPL
706 Flightline Drive
Spring Branch, TX 78070
brian at lloyd.com
+1.916.877.5067
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