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    Re: eLoran and electronic compasses
    From: Lu Abel
    Date: 2008 Apr 27, 20:21 -0700

    Thanks, Nicol�s!   An impressive bit of work in Dr Pelgrum's thesis! 
    
    For those who don't want to read the whole 200 pages, the thesis is an 
    investigation of many aspects of improving Loran performance using 21st 
    century technologies -- for example, various sorts of signal processing 
    to eliminating noise and interference.   A major portion of the thesis 
    is devoted to the introduction of a non-traditional antenna for 
    receiving Loran signals (the equivalent of a "loop antenna" found in old 
    RDFs versus the whip antenna standard with traditional Loran 
    receivers).   These antennas are smaller (potentially allowing for a 
    "handheld" Loran) and have RDF capabilities (which in turn allows for an 
    Loran-based electronic compass as I speculated).  Many real world tests 
    were conducted with this new form of antenna, both comparing it to the 
    traditional whip antenna and demonstrating new capabilities such as a 
    Loran-based electronic compass as Nicol�s noted.
    
    Lu Abel
    
    Nicol�s de Hilster wrote:
    > 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.
    >
    > Nicol�s
    >
    >
    > 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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