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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Threats to GPS and introduction of eLORAN
From: Lu Abel
Date: 2016 Jan 31, 17:09 -0800
From: Lu Abel
Date: 2016 Jan 31, 17:09 -0800
Before the advent of GPS, I had two Loran-C receivers aboard my 1980 sailboat (which I still own and love). The first cost nearly $2000 because it had the new-fangled feature of displaying one's lat/long instead of merely one's hyperbolic coordinates. It was typically off by a quarter-mile because it did not have ASF correction (if I recall correctly, "Secondary Factor" correction in Loran-C compensates for the fact that radio waves travel more slowly through air than a vacuum, while "Additional Secondary Factor" compensates for the fact that the conductivity of the earth (Loran-C waves hug the earth) slows them by an additional amount; SF can be calculated but ASF has to be based on on-the-ground measurements). However, the error was quite consistent, not only repeatable but consistent over 50 to 100 miles. Many's the time I navigated successfully for an entire day's journey in pea-soup fog. As I used to explain to people, "if you break the end of a yardstick, you can still measure distance with it, you just have to remember that it starts with 2 and not 0." In fact, I recall repeatedly logging the "slightly-off as shown by the Loran receiver" position of a sea buoy and wondering why I was getting a position that varied by 0.01 minutes or so -- until I realized that the buoy was in 100 ft of water and was simply swinging on its chain with the tide! After 15 years of service the first set, filled with transistors and coils, gave up the ghost and I bought a brand new one. This was a tenth of the volume and displayed lat/long spot on, thanks to built-in ASF correction tables. I still have it somewhere, waiting for Loran to be resurrected. GPS is a miracle of modern technology. But I do wish there were a reliable electronic backup....