[time-nuts] Re: Eloran long test from now to August or September.

[Poul-Henning Kamp]

> Interesting observation:  The Austron 2100F stays locked even
> with all my local noise sources turned on and the LORAN pulse being
> obscured (on the scope) by noise pulses.

That is by design.

Back when LORAN-C was designed, the VLF spectrum was considerbly
more crowded by non-random RFI than today.

Although they didnt call it that at the time, the combination of
the GRI, pulse-shape and polarity coding makes LORAN-C a spread-spectrum
signal.

With the exception of badly chosen XX00 GRI's there are literally
no man-made noise sources which survive the de-spreading operation.

The European "NELS" switch to four-digit prime-number GRI's were
made to make it even more robust, unfortunately that also made
European Loran-C robust against any users with existing receivers.

The one minor flaw in the design of the Loran-C signal is that
the master signal pulses are not balanced, so only the slave
signal have the deep null at precisely 100kHz.

See:

	http://phk.freebsd.dk/loran-c/theoretical_spectrum/



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