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0answers
48 views

Is the inducing signal weakened to the extent it induces a signal in the receiving antenna?

Silly question ... An antenna is necessary to receive a transmitted signal from atmosphere, or otherwise. The transmitted signal weakens as it travels through the atmosphere. When the signal ...
0
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1answer
77 views

Numb3rs TV series - Antenna

Most of you might have watched the TV series 'Numb3rs'. http://en.wikipedia.org/wiki/Numb3rs In one of those episodes they were discussing about how to capture the contents on the screen of a ...
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1answer
2k views

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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1answer
108 views

Getting a given wavelength radio signal given an antenna with real-world constraints

Supposing you are given a transmitting antenna of whatever type of metal is most commonly used these days, and supposing that you are applying an AC current with the intent of transmitting a 1 m ...
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2answers
15k 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 ...
1
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0answers
133 views

Can mu-metal reduce the negative effect of metal close to low frequency RFID antennas?

I have an 134.2 khz RFID antenna for sport events which is basically a 1x1 meter square sheet of rubber with 3 loops of antenna cable embedded. The problem is that the transponder recognition range is ...
4
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2answers
637 views

Radio communication and antennas

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 ...
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2answers
321 views

Quantum Mechanics- Antenna emitting electromagnetic radiation

Radio signals are being transmitted in a frequency of $ 8.4 \times 10^9 \text{s}^{-1} $ and being received by an antenna that is capable of receiving power of $ 4 \times 10^{-21} \text{Watt} $ ($ 1 \, ...
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2answers
103 views

What is difference between the miltary radar in 1940's from commercial antenna that is for the use of TV

What is difference between the miltary radar in 1940's from commercial antenna that is for the use of TV? I have read article from some of the WW2 history website that call the German radar the ...
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1answer
99 views

Is this claim from historician true for physicist point of view?

"The original Naxos I had a vertically polarized antenna, with poor results as the British radars initially used horizontal polarisation. (This seems to have been a case of the German designers being ...
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2answers
2k views

How to capture electomagnetic radiation/waves?

If I wanted to find out what kind of electomagnetic waves "travel" through my room at which frequency, what kind of equipment would I need? Suppose I want to view frequencies from 0 Hz to 6 GHz.
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1answer
941 views

What are the optimal shapes, if any, for fractal antennae?

A DIY fractal antenna project is described at http://www.htpc-diy.com/2012/04/diy-flexible-fractal-window-hdtv.html Mainly idle curiosity, but I was wondering what the principles behind these might ...
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2answers
1k views

How is antenna gain correlated to beam width?

Let's say you have two dipole type antennas. Antenna A has a gain of 2.15 dBi, a horizontal beam width of 360 deg and a vertical beam width of 45 deg. Antenna B is similar to antenna A, but has a ...
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3answers
3k views

Geometry of wireless signal strength

How does wireless signal strength correspond to distance? RSSI lies between -100 and 0 (at least, on my computer). Let's say I walk a distance x towards the router, and my RSSI goes from -60 to -50. ...
2
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4answers
2k views

Some questions about car radio and cellphone antennas

1-Why the antenna of the radio of cars is located outside the car and not inside? 2-If the answer to 1 is because that cars are like Faraday cages then how come my cell phone can receive signal ...
2
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1answer
1k views

How does holographic radar work?

I'm trying to figure out how the mechanics of holographic radar work. AFAIK there is a continuous 3d transmission signal (a dome-shaped antenna?) But because there isn't a direction or time-domain, ...
3
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2answers
523 views

Near-field around parabolic antenna?

Having a discussion at work about the $H$-field around a big parabolic antenna. All of the safety tests done around the antenna only mention $E$-Field. They state in the radiating near-field the $E$ ...
6
votes
1answer
459 views

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 ...
6
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1answer
4k views

Adverse Health Effects of Strong Radio Waves

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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3answers
1k views

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?
6
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1answer
340 views

How is an inflatable parabolic antenna created?

I'm intrigued by this, and how it would work:- 3 sub-questions if I may: Construction: As I understand it's a flexible sphere constrained by a rigid edge. a. Do we simply glue 2 flat circular ...
8
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1answer
5k views

How does a digital radio tuner work?

I believe I understand how tuning a radio with an analog tuner works: turning the dial physically changes the length of the antenna, which determines which broadcast wavelength will resonate in the ...
7
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3answers
2k views

How do radio telescopes work?

If I search online for how radio telescopes work, the found articles talk about how RF is on the spectrum, etc, how the parabolic collector is the aperture which contributes to the sensitivity and ...
29
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3answers
3k 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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1answer
465 views

What is the effect of ice on an antenna?

A local FM radio station transmitting at 89.3 MHz recently announced that it would be running at 50% power due to freezing weather and a forecast of ice accumulation, as "when ice is forecast ... it ...