[time-nuts] WAAS.....

[SAIDJACK at aol.com]

The latest receivers are surprisingly resilient to GPS jamming.
 
We tried jamming effects on all sorts of different GPS units  ourselves, 
and the M12's go out right away for example, while the uBlox units  are tough 
to jam. The new generation 7 ublox with Glonass etc should be even  harder 
to jam if programmed properly.
 
Attached is a sample plot showing GPS number of sats over a 1173 hours time 
 frame (49 days) of a FireFly-IIA unit sitting in our lab with an older 
(and more  jamming-sensitive) uBlox-5 in it. The antenna is simply a small 
cheap  magnetic puck sitting on top of the two-story roof, and the roof is 
facing  a highway. There was not a single instance of complete GPS Sat loss of 
lock  during that time frame, even though the antenna sits only a couple 100 
feet away  from from Highway 17 which has jammers on it that we can see pass 
by on other  GPS units.
 
Please note that this version of GPSCon was updated to be able to show 16  
sats in the SatCount by dividing the indicated number of sats by 2 rather 
than  just showing a total of only 8 sats, but the indicator still says 8 sats 
max. So  the variations in sats tracked are actually going from about 11 to 
16 during the  test. We had requested this change to GPSCon so it could 
support our 16 channel  status output.
 
It may be worth a try to get an eval kit of the latest uBlox chipset  
available to see how that handles typical known nuisance jamming  scenarios.
 
Bye,
Said
 
 
 
In a message dated 1/9/2014 11:00:20 Pacific Standard Time, brian at lloyd.com 
 writes:

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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