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Registered Member #498
Joined: Sun Nov 19 2006, 06:00PM
Location: Bay Area
Posts: 19
How big would a tinfoil square need to be to light an LED if one terminal was connected to the square and one to ground? I live in a suburban area several miles from the nearest broadcast transmitter, but there are many other radios around, and I can cheat if need be (handheld ham radio). How big would I need to make the sheet? (This is for a school project. )
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Check this thread it contains lots of ways to light an LED off free energy, and I think it also has a couple of examples of exactly what you want to do. In a nutshell, it is not only the size of the sqare that matters, but you can use a wire-loop antenna to greater effect, or connect various other circuitry to boost the efficiency of your antenna.
Registered Member #16
Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554
Indeed, just making a square as large as possible isn't going to help much. A more effective approach would be to determine which segment of the RF spectrum has the highest field strength in your area. For most people its the AM or FM broadcast band, as few other services provide 100% duty cycle. A resonant antenna on the band with the highest field strength is likely to produce the best results.
Another option would just be a very very wide band antenna like a long wire dipole. a 260' dipole up a few 10s of feet should give you a pretty good start. For more omni-directionality (dipoles are pretty broad-sided) something like a loop might be a better idea. The general idea is to keep reactance low, while maximizing overall surface area, and providing a balanced antenna.
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Harvesting wasted RF energy?
)
