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".
Read more about this topic: Crystal Radio
Famous quotes containing the words power and/or source:
“The dissident does not operate in the realm of genuine power at all. He is not seeking power. He has no desire for office and does not gather votes. He does not attempt to charm the public, he offers nothing and promises nothing. He can offer, if anything, only his own skin—and he offers it solely because he has no other way of affirming the truth he stands for. His actions simply articulate his dignity as a citizen, regardless of the cost.”
—Václav Havel (b. 1936)
“Nothing could be more inappropriate to American literature than its English source since the Americans are not British in sensibility.”
—Wallace Stevens (1879–1955)