Page "Crystal radio" Paragraph 67

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 .< ref > QST Radio Magazine January 2007, " High Sensitivity Crystal Set " < http :// www. arrl. org / files / file / Technology / tis / info / pdf / culter. pdf ></ ref > This history continues now with designs as elaborate as " inverted two-wave switching power unit ".