Welcome to the NavList Message Boards.


A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Add Images & Files
    Re: Warning from the architect of GPS
    From: Brad Morris
    Date: 2014 Feb 14, 14:44 -0500

    Hi Geoffrey

    I agree that high end military systems can defeat jamming.  A directional antenna increases the signal to noise ratio.  This assumes that you know where you are such that you *can* point them accurately.

    In an all out confrontation with a space faring opponent, one of the primary targets will be the satellites themselves.  No nation will allow itself to be picked apart with precision munitions while it has recourse to eliminate that GPS precision.  China has demonstrated this capability, as has the US.  I believe Russia has this capability, while other nations *could* develop it.  Its not impossible, just very difficult. 

    But all this is neither here nor there.  The thrust of the article is the concern about the affect on civilian GPS reception.  I'm a civilian.  My GPS devices have omni directional antennas.  Most civilian GPS devices (and many military GPS receivers I have handled) are omni directional.  A powerful transmitter on the same narrow band of frequencies will have a large noise component compared to a weak signal component.  The GPS signal *is* very weak.  Hence, the devices cannot receive the information from the satellites.  Its standard RF engineering.   Increase gain of signal whilst suppressing noise.  Hard to do that if your receiver has an omni directional antenna. 

    The article stresses the time component received as the main concern.  That is true if that was your sole source of accurate time.  But accurate time is also available over the internet, over the cell network and other places.  Most maintain a local clock which is sync'd periodically to a master clock.  So the jamming would have to be persistent and extremely widespread (like satellite elimination) in combination with internet suppression to accommodate the concern of the author.


    On Feb 14, 2014 7:37 AM, "Geoffrey Kolbe" <geoffreykolbe---.com> wrote:

    On 14/02/2014 02:06, Brad Morris wrote:
    > Widespread jamming requires a series of powerful transmitters (or just
    > one).  No big secret there.
    Actually, it is not quite as simple as that. Large and expensive systems
    that depend on GPS for navigation can use highly directional antennae to
    track the satellites using the ephemerides that are constantly
    downloaded to the receiver. This makes GPS reasonably jamming-proof.
    As I reported earlier, trials were done on one of the larger UK warships
    and the most determined effort to jam the GPS moved the ship a virtual 8
    Geoffrey Kolbe
    Dr Geoffrey Kolbe, Riccarton Farm, Newcastleton, TD9 0SN
    Tel: 013873 76715 Mob: 07811 154621

    View and reply to this message: http://fer3.com/arc/m2.aspx?i=126895

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.

    Email Settings

    Posting Code:

    Custom Index

    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site