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    Re: Dependence on GPS
    From: Lu Abel
    Date: 2009 Oct 30, 20:01 -0700

    Excellent points, Frank!   One of the big vulnerabilities of GPS is its 
    incredibly low signal strength at the receiver.  It actually has a 
    NEGATIVE signal-to-noise ratio, only sophisticated signal processing can 
    identify and hone in on the actual GPS signal.   In the GPS World 
    article, it was noted that a jammer emitting only milliwatts of power 
    could jam GPS over an area of several miles; such a transmitter would be 
    almost impossible to locate -- and its low power consumption would allow 
    it to run for weeks on ordinary batteries.    Aircraft navigation is 
    becoming increasingly dependent on GPS; imagine putting one of these in 
    a piece of checked luggage on an airliner!!
    For a real-world story about the vulnerability of GPS to even 
    inadvertent jamming and the difficulty of identifying the jammer, one 
    has to look no further than the story of the jamming of GPS signals in 
    Moss Landing Harbor in California.   
    The Monterey Bay Aquarium Research Institutes's vessel reported 
    consistent loss of GPS closer than about two miles from its home dock in 
    Moss Landing.  After a lot of effort by the San Francisco FCC office, 
    electronics experts from the Naval Postgraduate Research Center in 
    Monterey, and MBARI itself (along with a lot of sophisticated equipment) 
    the jamming was identified as coming from a TV antenna preamplifier used 
    by a live-aboard.   But wait, there's more.   Even after turning that 
    antenna preamp off, some jamming continued.   A second TV pre-amp was 
    also found to be jamming GPS!   And when that was turned off, yet a 
    third jammer was identified.   The design of all three pre-amps had 
    passed FCC scrutiny (there are federal standards to insure that such 
    pre-amps do not emit signals on GPS frequencies), but lack of quality 
    control in their manufacture had caused them to emit signals in the GPS 
    Anyone for eLoran??   It uses strong, terrestrial signals; jamming or 
    spoofing would be almost impossible.
    frankreed@HistoricalAtlas.com wrote:
    > Hi John, you wrote:
    > "It wasn't an issue of the conditions of the moment, but rather what I 
    suspect was the build-up of crud on the receiver over time that led to a 
    failure.   After two failures, I threw in the towel on the devices.  "
    > There's no doubt that GPS receivers of all stripes do fail. And a big issue 
    here is expense. If they fail with high-enough frequency, then we are thrown 
    back on traditional navigation just as a matter of economic necessity. 
    > All technology fails. Chronometers used to fail quite regularly, and in a 
    way that is far more dangerous than the failure of GPS (a GPS receiver will 
    almost always fail completely with an obvious indication that it is dead, 
    while a chronometer will degrade to dangerous performance without any visible 
    indication). But that doesn't mean we should avoid chronometers, nor does it 
    mean you should abandon GPS. The trick is to use it in such a way that limits 
    failures. Those dry pouches work, for example. Also, by far your best defense 
    is to carry a spare. The spare should be a different make and model and 
    stored in a different way from your main receiver to avoid the trap of 
    identical failure modes. It should also be stored in a small metal case to 
    serve as a Faraday cage.
    > Now of course this is NavList, so we're all about traditional methods of 
    navigation, but if you're out there risking life and limb, I personally would 
    never suggest to anyone that they use anything but the best available 
    technology, and that they should back that up by the best available 
    technology. There's no reason to risk your life or anyone else's for the sake 
    of an enthusiasm for traditional navigation. And other people's lives *are* 
    involved whether we like it or not. If you go missing for some extended 
    period of time, unless you're heading out on the water without telling a 
    soul, the Coast Guard will eventually come looking for you. The lives of 
    those searchers are then at risk (see yesterday's news from California 
    regarding a Coast Guard C-130).
    > So far we're talking about the failure of GPS receivers. They do fail, and 
    you can be prepared for that failure by carrying a spare GPS receiver. Peter 
    tells us that he has had multiple GPS receivers all fail all at once. That 
    kind of astronomically improbable bad luck seems to strike certain people, 
    but it's not the sort of thing that could be considered normal. Only an 
    electical shock could kill multiple receivers at once under normal rules of 
    "luck", and to defend against that possibility the solution is to keep your 
    spare GPS in a metal box to serve as a Faraday cage (does anyone sell this as 
    a standard item?). But beyond receiver failure, there's a much less likely 
    yet still important risk that the GPS signal itself might fail. There are 
    cases where you might have a somewhat degraded position accuracy if one or 
    more satellites fails, but those are temporary conditions and apparently very 
    rare. Of greater concern is the prospect that GPS signals might be jammed 
    over some region, perhaps dozens of miles in extent, for a military or 
    criminal purpose. I'm not talking about a direct military assault on the 
    satellites or the ground stations themselves. If that happens, we're looking 
    at war and we'll have bigger things to worry about. Instead consider a 
    scenario where someone holds a major port hostage by planting dozens of 
    concealed remote-controlled GPS jammers and then issues a demand: pay up and 
    you get your GPS signals back. Tracking down jammers is not easy... good luck 
    to whoever faces this scenario when it finally happens. Further, as 
    governments attempt to use GPS for enforcement (tagging criminals on 
    probation, e.g. or tagging ordinary vehicles for road taxes), there will be 
    an inevitable rise in the use of jammers and also GPS signal spoofers. The 
    latter are even more worrisome since they would yield erroneous positions in 
    receivers that appear to be functioning correctly. There are always things to 
    worry about, and for GPS and other such signals, the future may be worse than 
    the present.
    > The current issue of "GPS World," in which long-time NavList member Richard 
    Langley has a monthly column, has a brief and interesting article about GPS 
    jammers and spoofers. That's what got me thinking about criminal scenarios as 
    described above.
    > -FER
    > >
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