Use As A Power Source
A crystal radio tuned to a strong local transmitter can be used just as a power source for a second amplified receiver for distant stations that cannot be heard with a plain crystal radio.
There is a long history of unsuccessful attempts and unverified claims to recover the power in the carrier of the received signal itself. Traditional crystal sets use half-wave rectifiers. As AM signals have a modulation factor of only 30% by voltage at peaks, no more than 9% of received signal power is actual audio information, and 91% is just rectified DC voltage. Given that the audio signal is unlikely to be at peak all the time, the ratio of energy is, in practice, even greater. Considerable effort was made to convert this DC voltage into sound energy. Some earlier attempts include a one-transistor amplifier in 1966. Sometimes efforts to recover this power are confused with other efforts to produce a more efficient detection. This history continues now with designs as elaborate as "inverted two-wave switching power unit".
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—Friedrich Nietzsche (1844–1900)
“Being the dependents of the general government, and looking to its treasury as the source of all their emoluments, the state officers, under whatever names they might pass and by whatever forms their duties might be prescribed, would in effect be the mere stipendiaries and instruments of the central power.”
—Andrew Jackson (1767–1845)