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, [email protected] writes:
On Thu, Jan 9, 2014 at 12:21 PM, Hal Murray <[email protected]> wrote: > > [email protected] 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 [email protected] +1.916.877.5067 _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
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