[freebeard]

Doesn't have to.

en.wikipedia.org/wiki/Foxhole_radio

The foxhole radio was a crude crystal radio which used a safety razor blade as a radio wave detector with the blade acting as the crystal, and a wire, safety pin, or, later, a graphite pencil lead serving as the cat's whisker.[3]

The foxhole radio, like a mineral crystal radio receiver, had no power source and ran off the power received from the radio station.
....
The maker of the first foxhole radio is unknown, but it was almost certainly invented by a soldier stationed at the Anzio beachhead during the stalemate of February – May 1944.[1] One of the first newspaper articles about a foxhole radio ran in the New York Times April 29, 1944.[4] That radio was built by Private Eldon Phelps of Enid, Oklahoma, who later claimed to have invented the design.

edit:

Sometimes I think the most practical way of obtaining my dream car would be to just build my own.

Myself also. I'd want a Basalt fiber monocoque 12/10ths scale Schwimmwagen hull with an electric front axle.

2nd edit: Semi-retractable flotation tires and steerable electric [hubless] hydrojet thrusters.