# Tagged Questions

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### Radio antenna producing waves in the visible spectrum [closed]

If a radio could produce waves in the visible light spectrum, what would the result be? This is a thought experiment that I've pondered for a few years now. I realize there are a few/many real-world ...
5k views

### Can I use an antenna as a light source?

Can I use a normal metal antenna to emit visible light?
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### Radio waves and frequency of photon

How radio waves create the current in antenna in terms of photons? If it is Compton scattering then why is not changed the freuency of photons?
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### Detectability of interstellar messages

Recently a debate started whether it is a good idea to send more messages into space in the hope of having alien civilizations receive them. There are some predecessors, most notably the 1974 Arecibo ...
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### Radio antennas that are much shorter than the wavelength

From my limited experience with ham radio when I was a kid, I expect transmitting and receiving antennas to have lengths that are on the same order of magnitude as the wavelength, and in fact I recall ...
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### Effective aperture of isotropic antenna

I have always taken for granted that 'the aperture of a loss-less isotropic antenna is $\dfrac {\lambda^2} {4\pi}$'. On a whim, I tried to look up how this expression was derived, but so far I have ...
28k views

### Why is Near Field Communication (NFC) range limited to about 20cm?

Near Field Communication (NFC) operates at 13.56 MHz. Near Field is the region situated at a distance r << λ λ = c/f ...
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A while ago, I was hiking near the Hollywood Sign in Los Angeles. When I got to the sign, I found out it was fenced off; with several signs and a security camera promising prompt enforcement. As I was ...
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Power = current times voltage. However current requires a complete circuit to 'flow'. How can a 1,000 Watt antenna work if the output of the transmitter is connected to a single emitting wire or ...
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### What happens to a photon after it is absorbed by an antenna?

I recently have read about interception of wireless information, however this mentions that people can intercept the information, and then somehow the recipient also gets the information. Regardless ...
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### How do EM waves get detached from an antenna?

How does an electro-magnetic waves get detached from an antenna and spread to the space? While an antenna receives an EM wave, which quantity of the EM wave (electric or magnetic) is used for ...
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### Why are fractal geometries useful for compact antenna design?

While most of what I've read about fractals has been dubious in nature, over the years, I keep hearing that these sorts of self-similar (or approximately self-similar) geometries are useful in the ...
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I'm trying to understand how an antenna is able to understand, but have a few quesions: I understand that for an antenna to distinguish between 2 (or more) signals, they have to be in different ...