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earlz wrote:The way I understand diodes though is they keep current from going one way, they don't necessarily reverse it though.. or could that be done with two diodes?

Actually you need 4 of them. Take a look at this power supply.

You need 4 diodes to rectify AC, like this But you can not dynamically switch the direction of the output current without exchanging the output poles. To switch the direction of the current dynamically, for example, to generate "AC" from DC, you need something like transistors or relays...

Utter BS. You only need 4 to do a full-wave rectification (and even then it's not perfect). You can achieve rectification with just 1.

Solar wrote:

earlz wrote:[barn lightbulbs]

Is it possible that this really happened?

Absolutely.

If you live close to a strong radio station, you can light a bulb simply by attaching it to a length of (unshielded) cable. (This is illegal, at least here, but possible.) Radio signals are electromagnetic waves, and when you receive them via an antenna what you're doing is transforming those waves into electricity, which your radio then amplifies and makes audible through the speakers.

Illegal on what basis? The only reason I can see for that to be illegal is the danger posed by a lightning strike.

Owen wrote:Illegal on what basis?

Stealing energy from the EM field of the radio transmitter; energy that should go into transmitting the signal to customers receiving it via a radio (instead of a lightbulb).

Radio waves don't work that way. By that definition any grounded metal pole is stealing energy by converting it into heat.

I have a feeling those metal poles you are referring to aren't purposely trying to rip off the transmitter.

Owen wrote:Radio waves don't work that way.

Grounded metal poles are incredibly common. For a start, there are a lot of street lights, signs, and so on, which are just metal poles in the ground. They are far more effective at blocking radio waves. And how effective are they? Not very.

It sounds like an urban legend, so I'm not sure if it is true, however the story is:

Valmiera's (a city in my country) hospital was constructed in the 70's. It was located about 500m from a local TV re-transmitter. The legend says there were many accidents as sparks from the crane hit some workers. In the end they had to shut down most of the transmitters until construction was done.

As I said, I'm not sure if this story is real (yet, re-transmitter and hospital are still there), but I found it interesting

Given from a TV series I've seen (can't recall the name), they pulled current out of the air by suspending a huge coil of wire between four trees. The output was just enough to construct a small transmitter to send morse clicks over a few hundred meters.

Now try that with a few batteries.