Current in an antenna
Current in an antenna
(OP)
Im pretty ignorant of EE...
But if I have just a simple antenna thats recieving radio waves what do I have to do with the the antenna to measure a current through it that's induced solely from the radio waves. For example complete a circuit with a resistance, ground it, etc??? Thanks and I'll remind you of my limited knowledge of electrical design
But if I have just a simple antenna thats recieving radio waves what do I have to do with the the antenna to measure a current through it that's induced solely from the radio waves. For example complete a circuit with a resistance, ground it, etc??? Thanks and I'll remind you of my limited knowledge of electrical design





RE: Current in an antenna
TTFN
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RE: Current in an antenna
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Current in an antenna
RE: Current in an antenna
Bill
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"Why not the best?"
Jimmy Carter
RE: Current in an antenna
RE: Current in an antenna
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Current in an antenna
RE: Current in an antenna
The effect may be enhanced by several techniques such as length, spacing, orientation, multiplication and directionality.
A yagi is an arrangement of passive elements which are cut and spaced so as to effectively re-radiate the radio signal.
Now that we have enhanced the current in the antenna, this current may be detected and amplified.
In some instances the current may be enough to directly power very low drain and/or efficient devices.
A dish reflects a radio signal into a tight beam making transmission and reception much more efficient.
Anecdote: In the early days of satellite TV some small fiber-glass dishes hit the market. They didn't work. The builder had looked at a dish and said;
"I can do that."
He bought a sample dish for a pattern and starting building dishes. He was not aware that there is an internal conductive layer in plastic and fiber-glass dishes. Without the conductive layer the dishes were useless.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Current in an antenna
Have a look at the wiki:
http://en.wikipedia.org/wiki/File:CrystalRadio.jpg
There are lots of other descriptive/instructional/video presentations if you google: building a crystal radio
Here's one friendly one:
http://scitoys.com/scitoys/scitoys/radio/homemade_...
The device captures radio energy with an antenna, pairs it with a resonant circuit, filters it to extract the audio-frequency signal, and expels enough power to produce audio in a set of headphones. No batteries involved.
Now, if you go a step further, you could imagine rectifying the audio frequency component (could be done at radio frequency too) to DC aand directly powering a load that is no larger than the headphone load. If your load is larger and intermittent, the rectified DC might be used for charging a battery or capacitor.
Well, it has been a long, long time since I played with radios and understood the workings. I hope I haven't embarrassed myself here.
Best to you,
Goober Dave
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RE: Current in an antenna
I'm not one of those that worries too much about "the dangers" of EM radiation, but if there were enough around to power light bulbs - then even I would move.
RE: Current in an antenna
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RE: Current in an antenna
High impedance headphones or earphone. Typically a crystal (piezo electric) earphone is used. Crystal radios in typical circumstances will not provide enough output to work with modern, common, low impedance headphones.
RE: Current in an antenna
BTDT in junior high. Whatever comes out of a crystal radio requires active amplification to drive anything beyond a crystal headphones.
In any case, "I realy just want to know if I have a room full of radio waves and a metal pole what do I need to do generate a 'noticible' current." isn't going to happen without a receiver and amplification.
See: http://radio-locator.com/info/KPCC-FM The effective radiated power, WHICH IS AT THE TRANSMITTER, is only 600W. Assuming that's at a 1-m radius, being 30 miles away means that at the receiver, we get a power density of 20 nW/m^2. Which means that a 1 m^2 antenna can capture, at most, 20nW of power. The actual power might be somewhat higher, since the transmitter antenna isn't going to be completely omnidirectional, but we're only talking about an order of magnitude or so, call it 200 nW. That's still not going to drive any light of any sort.
TTFN
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RE: Current in an antenna
Wonder if anyone ever thought of using a crystal radio for new fangled 'energy harvesting' or if that would be considered cheating? bet it's a patentable idea for someone....
RE: Current in an antenna
Thanks for the insight, I agree with it. Keep in mind, though that I was not suggesting that a crystal radio setup would solve the OP's desire to power his device. It was to illustrate one answer to his second post:
In that sense, the crystal radio does convert received RF energy into a tiny bit of useful work. Same with passive RFID tags, but they don't lend themselves well to an illustration of the technology.
Powercast has made a step forward -- http://www.slideshare.net/Powercast/pwst-and-high-...
Best to you,
Goober Dave
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RE: Current in an antenna
is, I think, the issue at hand. He wants the theory behind something that he thinks he's seen, but there's no there, there.
TTFN
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RE: Current in an antenna
http://electronics.howstuffworks.com/everyday-tech...
Dan - Owner
http://www.Hi-TecDesigns.com