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

[Poul-Henning Kamp]

> But that said the lower in frequency the system is the harder it is to get
> something to radiate.

At 60 kHz the gap between ocean and the ionosphere is a waveguide,
which bends the signal to match the Earth's curvature, so
there is no theoretical limit to distance, as long as it is over
an ocean.

That is why the first commercial radio-telephone connection between
USA and UK in the 1920ies used 60 kHz.

At 100kHz there is no significant waveguide effect, quite the
contrary, you get "skywave" reflections, in particular at night.

Here is a recording of the "skywave dance" on a typical night at a
distance of approx 200km from the transmitter:

	https://phk.freebsd.dk/AducLoran/animation2.gif

Loran-C uses the "3rd positive zero-crossing" as reference because
it is impossible for the skywave to arrive so early, given the height
of the ionosphere.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.