Discussion in 'General Electronics Chat' started by cjdelphi, Feb 3, 2011.

1. ### cjdelphi Thread Starter New Member

Mar 26, 2009
272
2
ok other than the legality of this device, put to one side, is this possible? simply by plucking excess radio waves out of the air, leaked voltage on the 50/60hz scale if just walking around 'feel safe ' knowing your watch is soaking up some 'bad' electromagnetic radiation, so yes instead of having your brain cooked very slowly, have a stylish watch to soak up that bad energy and making you look cool

Jokes aside, how plausible is this? enough to pluck out to keep a battery charged? obviously you could stick your hand near the microwave to give it a bit of a charge, make a phone (your battery power on transmit!)

People of the UK pay a TV license every year, how exactly would it be 'stealing' if you pay for that frequency just because you happen to be in the street does not mean you can't benefit from it by giving your watch a bit of a charge

2. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
I believe the power levels are insufficient making any kind of harvesting scheme a complete waste of time. The only way a radio receiver is able to reproduce weak signals is to use a power supply to amplify, detect, and reproduce microwatt signals into something that can drive a pair of headphones.

Look at the specifications on a typical LCD Display. It might operate anywhere from 3.3 to 5.0 volts and consume 0.5 to 5 mA. Now lets try a back of the envelope calculation:

Code ( (Unknown Language)):
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2. 5.0 Volts * 5 mA = 25 milliwatts.
3.
A typical RF signal might be 35 microvolts into say 50 Ohms
Code ( (Unknown Language)):
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2. ((35 μV)^2) / 50 = 24.5 picowatts.
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The difference in power level is NINE orders of magnitude. Talk about Sisyphus pushing a boulder up a mountain -- this would be an example.

http://en.wikipedia.org/wiki/Sisyphus

Last edited: Feb 3, 2011

Mar 26, 2009
272
2
ah

4. ### Laserever New Member

Jan 21, 2010
5
0
Suppose he was able to grab anything at all being broadcast on the FM spectrum, and then rectify it.

He would need a tiny tuned antenna for every FM frequency being broadcast, but suppose he is in a large city where there is a station on just about every tuning increment.

Add up all those stations, and I suppose you'd still be horribly short for power...

5. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
The real problem is actually the same old problem that processes are not 100% efficient. Getting from minute power levels to usable power levels without using external power is just not practical.