Crystal Radio Antennas

A medium wave broadcast station antenna system generally comprises a ¼ λ vertical element
and earth.

It would not be wrong to infer that such an antenna would be ideal for a crystal radio.

Crystal Radio Antenna Arrangement
However, practical reasons necessitate use of a much shorter element, with a suitable loading
coil making it resonant at the desired frequency.

Good results would be obtained with an element not shorter than 60 feet.
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