From the Vault - featured items from our collection

Martian Crystal Radio (PH2014.12.1)

Martian Special Crystal Radio

This is a crystal radio set manufactured by Martian Manufacturing Company Limited out of Newark, New Jersey, USA. The radio needs no battery or power source and runs on the power received from radio waves by a long wire antenna. The antenna converts the energy in the electromagnetic radio waves striking it to an alternating electric current in the antenna, which is connected to the tuning coil. Since in a crystal radio all the power comes from the antenna, it is important that the antenna collect as much power from the radio wave as possible. The larger an antenna, the more power it can intercept. In addition, antennas are most efficient when their length is close to a multiple of a quarter-wavelength of the radio waves they are receiving. Since the length of the waves used with crystal radios is very long, AM broadcast band waves are 182-566 m long, out of a long as possible wire, in contrast to the whip antennas or ferrite loopstick antennas used in modern radios. A popular practice was to use existing large metal objects, such as bedsprings, fire escapes, and barbed wire fences as antennas.

To adjust the signal source a ‘cat’s whisker’ was moved across a crystal, in this case a bit of galena. When the whisker touches the galena it forms a crude and unstable point-contact metal-semiconductor junction, a Schottky barrier diode. The crystal requires just the right gentle pressure by the wire; too much pressure caused the device to conduct in both directions.

This object was purchased and used by a citizen of The Pas, Manitoba from 1924 - 1926. At the time it would have been quite a novelty. The son of the original owner donated this object to the Sam Waller Museum in December of 2014.

Added: December, 2014

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