One feature of the Crystal radio is that it needs no other power source but that received solely from the power of radio waves received by a wire antenna.
But it also requires good ground connection to work. This is not easily available for mobile use (except on seafaring ships ).
I wonder if there exists some (possibly more complex, possibly heavier, etc) counterpart that could be used without ground connection, and still work off radio wave power alone – say, on a blimp?
(please excuse the misnomer in the title but radio powered solely from the power of radio waves received by its antenna is a little too long for a title)
Best Answer
Yes, it is possible. Many antenna types are self-contained, in that they don't require a ground or use ground as one of the two connections where the signal appears between. Dipoles, folded dipoles, and loops are just three examples of such antennas.
The reason most crystal radios work with a long line antenna and the other connection ground is because that's a good way to intercept reasonably high RF power, relatively speaking. A dipole the full length of a blimp and hung below it might intercept enough RF power so that you can hear the demodulated signal with the right headphones. The orientation of the blimp would be important. It would pick up signals to the sides, but not directly in front or in back. There are other self-contained antennas that have other radiation patterns, but their shapes wouldn't be as compatible with the stucture of a blimp.
Polarization also matters. One problem with the blimp dipole is that it would pick up horizontally polarized transmissions. Most commercial AM, for example, are vertically polarized.
Of course the available power in the air is important too. Being close to a powerful transmitter helps a lot.
Back in grade school, I had a long line antenna out a window in my room to a shed in the back yard, maybe 60 feet long. I could pick up a 50 kW AM station from about 20 miles away reasonably well with a crystal radio and the right headphones. The orientation of the antenna was about right for the direction to the transmitter, but the polarization was opposite. There was apparently enough scatter and diffraction so that it still worked.