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    Re: GPS Reliability -- Warnings surely must be a HOAX
    From: John Brenneise
    Date: 2004 Jun 19, 19:31 -0700
    These warnings are undoubtedly a HOAX!!!
     
    Read the Bowditch chapter(s) on Electronic Navigation. 
     
    All GPS (Global Positioning System) satellites  transmit on the same two frequencies,  modulating a unique, per-satellite C/A (Course Acquisition) code onto their SPS (Standard Positioning Service) frequency signal.  Civilian GPS receivers, which use the SPS have internal knowledge of the C/A code for each satellite from which they are capable of receiving a signal. SPS receivers employ the C/A code to amplify the signal by constructive interference, thereby picking out a given satellite's signal from the "soup".
     
    As you can see, the satellites interfere with each other BY DESIGN. 
     
    The other frequency is used by the PPS (Precise Positioning Service) which is essentially the domain of military receivers, but is, nonetheless, also described in Bowditch.
     
    Additional information is available on a variety of web sites that describe the system.
     
    John Brenneise
    ----- Original Message -----
    Sent: Saturday, June 19, 2004 2:00 PM
    Subject: Re: GPS Reliability

    In the United Kingdom the Royal Institute of Navigation are issuing warnings on the vulnerability of GPS to loss of signal and interference.   The received GPS signal is so weak that any interference could stop the GPS receiver completely.
     
    With the GPS acting as a back up to normal navigational methods this is not so important.   However where navigation is 100% dependent on GPS this could be catastrophic!   Fortunately the GPS does not produce an error signal so when it is not working it should be relatively obvious.
     
     
    Philip Ouvry
     
    Perpignan
    France
       
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