By W.F. Blanchard

After the low frequency Loran trials of 1945 and the realization that pulse-envelope matching at low frequencies was not sufficiently accurate to be useful (in spite of which several companies were still producing envelope matching Loran-C receivers as late as 1980!), it was decided to try superimposing a low frequency modulation at around 200 Hz and use that for timing and possible resolution of the cyclic ambiguities at 100 kHz.

Several years of experimentation resulted in the realization that it was not going to work successfully, but the results indicated that the timing obtained from this modulation was probably good enough to resolve the ambiguities of much lower frequencies of, for instance, 10 kHz. Accordingly, a composite system was designed which radiated a 40 kHz signal modulated at 200 Hz and having bursts of 10 kHz superimposed. The 40 kHz  supplied the accuracy, the 10 kHz resolved the 40 kHz ambiguities, and the 200 Hz resolved the 10 kHz ambiguities. It was called Radux-Omega, but it was unsuccessful because the range of the 10 kHz signal greatly exceeded that of the 40 kHz, 'while the relatively short baselines needed at 40 kHz spoiled the possible geometric accuracy of 10 kHz at long ranges.


The Journal Of Navigation - Chapter 4.
W.F. Blanchard, Royal Institute of Navigation;
Vol 44, No. 3; Sept 1991. Used with permission.

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