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Why isn't light induced by an antenna

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thunkit
#1
Jul23-11, 01:27 PM
P: 8
I am sorry please delete this post if it has been already asked

Light is an electromagnetic wave right?

i havent have ever heard of light distorting or causing disturbances in antenna signal,why is it so isn't it also an electromagnetic wave?
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Clever-Name
#2
Jul23-11, 02:56 PM
P: 380
antennae are made to function at a specific wavelength (or frequency) of electromagnetic radiation, in the radio spectrum of EM radiation we're dealing with a wavelength between 1 millimeter to even hundreds of millimeters. The signal is propogated through the antenna by the oscillations of electrons at the corresponding frequency/phase/amplitude etc.

Light doesn't have any effect because it's effect would be tiny in comparison with what radio waves oscillate at. Light has a wavelength between 400-700nm give or take. Corresponding frequency range is just under 10^15 Hz.

The frequency range for radio waves is between 50MHz to 1000MHz (~10^8 to 10^9Hz). On the order of 7 orders of magnitude difference.

Light might have an effect on the oscillations of the electrons, but in the grand scheme of things it's miniscule in comparison to the effect radio waves will have.
jtbell
#3
Jul23-11, 03:11 PM
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Quote Quote by thunkit View Post
i havent have ever heard of light distorting or causing disturbances in antenna signal
Try to design an antenna whose resonant frequency is evenly remotely close to the frequency of light, namely a few hundred terahertz.

(WiFi antennas are merely a few gigahertz. You need to go about 100,000 times higher...)

schroder
#4
Jul23-11, 03:33 PM
P: 373
Why isn't light induced by an antenna

That depends upon what sort of antenna you had in mind. All parabolic antennas are excellent solar reflectors. For that reason the larger ones for satellite communication are usually painted with flat (non gloss) paint, and care is taken at the times of year when the sun happens to cross the geostationary arc and enters the look angle of the antenna. The subreflectors that are at the beam focus are usually made of fiberglass to resist the heat from the focused sunlight. A flashlight uses a parabolic reflector to focus the light and can be thought of as a “light antenna”.
thunkit
#5
Jul25-11, 01:12 AM
P: 8
thanks alot,i didnt know about that
i jus thought i never heard any disturbance in a radio or something when light is focussed on its antennas,lol
schroder
#6
Jul25-11, 04:06 AM
P: 373
Quote Quote by thunkit View Post
thanks alot,i didnt know about that
i jus thought i never heard any disturbance in a radio or something when light is focussed on its antennas,lol
The previous posts explained why that does not happen; the antenna is electrically too long for it to have resonance with the very short wavelength of light.
The parabolic dish antenna will reflect the light waves quite efficiently and it can pose a real problem for the satellite earth stations at certain times of year (during the spring and fall equinoxes). During those times the received signal is disturbed, and can be completely washed out by the solar interference.

Here is a link that has a bit more information about that:
http://engineering.learfield.com/sun-outages/


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