Svenska ElektronikForumet

Attempts at recovering RF carrier power

A crystal radio tuned to a strong local transmitter can be used just as a power source for a second amplified (often a power-efficient regenerative) receiver for distant stations that cannot be heard with a plain crystal radio.[4]

There is long history of less successful 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[citation needed], no more than 9% of received signal power (P = U2 / R) 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[5] amplifier in 1966. Sometimes efforts to recover this power are confused with other efforts to produce a more efficient detection.[6]. This history continues now with designs as elaborate as "inverted two-wave switching power unit"[4] and bridge amplifiers[citation needed].

At least one cellular phone manufacture is researching harvesting stray radio signals as a power source to charge their product's batteries. Prototypes are already able to absorb 5 to 10 milliwatts from the air.

Neondiod skrev:Vill ha en LED-nattlampa som drivs av telefonledningen, så jag behöver inte mer än 20mA.

TPF

Jag är intresserad av svenska telefonledningars egenskaper.