Re: What sources might generate a 1 Hz radio wave, that's 3 x 10e8 meters long?

A 1Hz alternating current would generate 1Hz electromagnetic 
wave. The difficulty is how to let it radiate efficiently.

Since the size of antennas significantly affects their 
capability of  radiating and receiving electromangetic waves,
and there seems no way to make an antenna large enough to
be comparable to the wavelength of 1Hz electromagnetic wave,
it is very hard to transmit/receive signals by using such
low frequency.

However, if your purpose is mainly to show the existence of
electromagnetic waves of such low frequency, you can use two
coils which are near to each other. Connect one coil with
a signal generator of 1Hz, connect another coil with an oscilloscope.
Since there is mutual inductance between these two coils,
the oscilloscope will show induced current of the same 
frequency.