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Re: eLoran and electronic compasses
From: Nicol�s de Hilster
Date: 2008 Apr 28, 08:40 +0200
From: Nicol�s de Hilster
Date: 2008 Apr 28, 08:40 +0200
Just to be complete for others that visit this list, a full reference to the dissertation: W.J. Pelgrum, "New Potential of Low-Frequency Radionavigation in the 21st Century", Bussum, The Netherlands, November 2006, ISBN 978-90-811198-1-8 (296p.). Lu Abel wrote: > 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 >>> >>> >>> >>> >>> >>> >>> >> >> >> > > > > > > > > --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---