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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)

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    \$\begingroup\$ I'd imagine that with a big enough AM loop antenna it'd probably work. Monopole (whip) antennas need some kind of ground plane to work properly (but it probably doesn't need to be the size of the earth). A balanced dipole would probably work too. \$\endgroup\$ – Sam Feb 23 '17 at 22:53
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    \$\begingroup\$ you need a double-sided Dipole antenna (like a half-wavelength) rather than the single-sided vertical antenna (that is quarter-wavelength) that substitutes the earth ground for half of the antenna. \$\endgroup\$ – robert bristow-johnson Feb 24 '17 at 4:04
  • \$\begingroup\$ @robertbristow-johnson If you've never built xtal radios, first research. AM broadcast band is 500KHz, halfwave 300 meters of wire. Crystal radios don't use halfwave or quarterwave antennas (The first one to employ a 1/4lambda vertical gndplane antenna could have famous a Youtube video to commemorate the event! No fair using any existing antenna, it has to be DIY) \$\endgroup\$ – wbeaty Dec 24 '19 at 9:05
  • \$\begingroup\$ 300 meters is quite possible if you have enough space. On the farm I hooked a crystal set up to our open wire telephone line, and the signal was strong enough to power a speaker from an AM station 20 miles away. \$\endgroup\$ – Bruce Abbott Dec 24 '19 at 10:33
  • \$\begingroup\$ @wbeaty, i dunno how old you are but i built a crystal radio (1N34 germanium diode) sometime ca. 1963. the antenna was a longwire and ground. but if you don't have ground, you need a dipole. i was also an amateur radio operator in the late 60s and early 70s, also an electrical engineer, and i know how antennas work. if you don't have ground, you need a dipole. \$\endgroup\$ – robert bristow-johnson Dec 24 '19 at 11:43
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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.

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If voyager using 20 watts of transmit power can be received from the edge of the solar system, clearly, having any form of earth connection is not vital. Remember that voyager also received an uplink from earth too.

A dipole antenna is balanced and doesn't need an earth connection. A parachutist with a walkie talkie with a monopole antenna doesn't need an earth connection either.

A crystal set uses an undersized monopole because a dipole would be twice the size and need a balanced to unbalanced (balun) converter to work optimally so these are hinderences. A monopole doesn't really need an earth but it does need a local earth plane that the monopole sees as an infinite earth. For a crystal set this "fake" earth plane would need to be about 1 wavelength in radius so, at a frequency of 1 MHz that makes it quite large and conveniently our planet makes life easy for a monopole.

It was the need for simplicity and convenience that pushed the crystal set to require a ground connection.

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I recall that early crystal radios sometimes used wide loop antennas (like a hula hoop, or a several-feet square diamond, or octagon. Or basket-weave coils many inches in diameter.) Look up: crystal radio loop antenna.

https://www.google.com/search?q=%22crystal+radio%22+loop+antenna+diamond&source=lnms&tbm=isch&sa=X

In early internet days some guy had a ferrite antenna, using a collection of inch-thick ferrite rods, in series segments totalling several feet long! (Also, I see a reference to "ferrite sleeve" antennas, so that might be another possibility.)

Hobbyist VLF antennas aren't possible? Since they're fifty miles wide? Nah, just build a tuned, short antenna, where the Electrical Aperture EA is far, far wider than the physical parts. Those antennas act as "wave-funnels," where they may be electrically a quarter-wave wide, even though they're physically only .0001-wave in width. Essentially, if you build any large VLF radio antenna project, it can also be tuned for AM band. Look for DIY groups doing "natural radio" or "diy vlf antenna," or perhaps "vlf antenna tutorial."

For small antennas like this, the Q-factor becomes critical, and the wire in the coil needs to be fairly thick (or use heavy copper tape, or litz wire found on eBay, or even some 1/8" copper fridge-tubing.)

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Loop antennas do not need a ground. The ferrite rod is a more compact form of loop antenna. I recently built a portable crystal set that operates a 800 ohm Philips HiZ loadspeaker via a fullwave germanium detector. The LXRX set had a 12turn loop antenna that was tuned with both sections of an old air spaced AMBC variable cap. Anyway you could hear the radio stations when you walk very close to the tower.

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My brother and I had a crystal radio set as young boys and we built an antenna consisting of 10 foot high poles around a half acre of our yard and back to our crystal set. We were picking up stations in UK, France, Spain, Italy and Japan from our location in Tampa, Florida! It was great and worked really great. It was almost as if you were in those locations listening to the radio - loud and clear!

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  • \$\begingroup\$ Roy, the question at the top of the page is, "Can unpowered radio work without ground connection?" Your 'answer' does not address this in any way. This is a question and answer site rather than a chat forum. Can you edit to answer the question or delete the post to save the moderators a job? \$\endgroup\$ – Transistor May 2 at 16:19

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