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    Re: eLoran and electronic compasses
    From: Nicol�s de Hilster
    Date: 2008 Apr 27, 20:10 +0200

    Please check http://jproc.ca/hyperbolic/loran_c_eloran.html
    At the bottom of that page you will find a link to a dissertation in 
    which, on page 122, the LF H-field antenna is described. This loop 
    antenna is not an omni-directional antenna and, when used in a dual loop 
    configuration, can be used as a heading device. On page 168 in fig 5-49 
    a graph is shown that, after calibration, compass errors are smaller 
    than 0.8 degrees. On page 175 it reads "With only factory calibration, 
    the Loran-derived compass heading had an offset of 2.8�, a standard 
    deviation of 3.9�, and a 95% error of 8.3� with respect to the Vector 
    Pro GPS compass. After field-calibration, these errors reduced to an 
    offset of -0.1�, a standard deviation of 0.5�, and a 95% heading error 
    of 1.1�...". The eLoran heading was checked against a Vector Pro GPS 
    heading device (which is a zero-baseline RTK heading device) with an 
    accuracy of 0.5 degrees.
    Lu Abel wrote:
    > A bit off topic, but ...
    > A friend sent me an article (perhaps more accurately described as a 
    > publicity release) about eLoran that claims its signal can be used in 
    > electronic compasses.   The precise sentence in the article is:  
    > "Moreover, eLORAN can do things GNSS cannot, such as acting as a static 
    > compass."
    > First of all, the statement about GPS is inaccurate, since one can buy 
    > electronic compasses that work even when they are static by comparing 
    > the phase differences between the receipt of GPS signals at two or three 
    > antennas separated by a foot or less.
    > What makes me very curious, though, is how an eLoran-based electronic 
    > compass would work.  
    > "GPS compasses" work by observing the phase differences between signals 
    > received at two or three different receivers, these phase differences 
    > give the direction to the satellite and by knowing its location in space 
    > it's simple math from there to calculate the direction of true north.   
    > But the phase difference method works only because GPS signals have such 
    > a short wavelength that there are considerable phase differences between 
    > signals received at antennas even a short distance apart.
    > I have not been able to find any information on how eLoran-based 
    > electronic compasses would work.   Loran signals are very 
    > long-wavelength signals (25,000 times the wavelength of GPS signals), so 
    > measuring their phase differences in any reasonably small electronic 
    > compass setup would seem impractical.
    > Maybe measure the bearing to each of the transmitters?   But I have a 
    > hard time believing that could be done accurately enough to create an 
    > electronic compass with sub-one-degree accuracy.
    > Can anyone point me to an explanation, or is the sentence I quoted above 
    > simply hyperbole from an eLoran supporter?
    > Thanks
    > Lu Abel
    > >
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