I remember the Navy used frequencies near 20 kHz to talk to submarines.
> The design you mention places the input impedance at 20 meg ohms. The long
> wire antenna varies but lets say 400ohms worst case. That would mean at 500W
> input to this antenna, the voltage would not be greater than 450 at 500kHz.
At 500 kHz, we have a wavelenght equal to 600 meters. This means that if you
have a 600 m long wire, the impedance at the ends will be very high.
If you feed that wire at 150 m or 450 m, the impedance will be very low.
> I'd investigate this a little more, by picking up a HAM book on
> some antenna theory and checking it out. Hey, maybe we
> can talk to each other around the world on 500kHz?
>
Don't you remember the old AM radios ? There are radio stations
beginning at 530 kHz, as I know.
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 ...
Marcelo Puhl
Ham Radio Station - PY3SS