Until this year, 500 kHz was an international marine distress
frequency. It may still be in the southern hemisphere, but it's been
discontinued in the north.
> At this low frequencies, the propagation is mainly terrestrial. But
you have to
> put out very large amounts of power to get some useable signal beyond
1000 km.
> I'm speaking on more than 100 kW ...
Yes, the propagation is abysmal, but the ships used CW Morse, which
doesn't carry much information. That's why it got dropped, in fact.
The thing I don't understand is how they got static-free reception at
that frequency without killing the intended signal as well.
-- A good traveller has no fixed plans and is not intent on arriving. --Lao Tzu