it is to do the emmisitivity and reflectivity, mostly reflectivity but emisitivity is related) of objects to specific frequencies.
shine white light on to a red house brick, the red bits are reflected, the reflectivity of photons in the red part of the spectrum is higher. and the brick heats up, other frequencies are obsorbed in to the object, increasing to a degree the kenetic energy, which then results in radiated heat (Ingra Red)
the frequency of the EM radiation you use has little effect on the amount of interference you recieve. the more important factor is the amount of noise in that band. eg a system that tries to transmit information by infra red is not the best choice for a coms system. IR is readily radiated by objects in our environment which means that bespite a wave length of about 800nm we can only transmit at a few bits/s or at most half a dozen megabit/s
there is a famious theorem in regards to the amount of information you can transmit in a specified chanel at a particular level of noise, it's called the Shannon Information Capacity Theorem.
C = B log(1+SNR)
C is the maximum capacity of the channel (bits per second), B is the bandwidth of the channel, usualy near enough to some percentage of the carrier, and SNR is the signal to noise ratio.
Also, a laser is a special form of coherent light. It just means that all the wavelengths in the beam of light are the same wavelength
not true light or any other em radiation that consists of a single wave length is simply monochromatic not necessarily laser. in a laser all the photons emitted are in phase.
Since the radio requires a specific band to tune in to, it makes sense that the broadcasting station not waste time generating unnecessary wavelengths and focus on only those wavelengths that correspond to our chosen band. This restricts us to AM (amplitude modulation) bands only, but since we're trying to get data signals and not Martian stereo there is no big loss.
Complete crap, generating wave lengths with a specific wave length does not restrict you to AM, PSK is a perfectly valid form of modulation for a single carrier environment not to forget other forms like PAM.
In fact a laser system based solely on the presence or absence of laser wavelengths that are transmitted in free space is an absolutely rotten idea. current photo detectors have no way of "synchronising" to the lased radiation they simple detect the presence or absence of a specific wavelength of light.
So why deal with visible light lasers when it could be invisible and work just as well?
because at a fundamental level the shorter the wave length used for transmission the higher the possible rate of transfer is.
is the parent thread actually basing his/her post on any information or are they simply trying to pass of there misguided opinions as fact, oh wait this is slash dot...
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shine white light on to a red house brick, the red bits are reflected, the reflectivity of photons in the red part of the spectrum is higher. and the brick heats up, other frequencies are obsorbed in to the object, increasing to a degree the kenetic energy, which then results in radiated heat (Ingra Red)
the frequency of the EM radiation you use has little effect on the amount of interference you recieve. the more important factor is the amount of noise in that band. eg a system that tries to transmit information by infra red is not the best choice for a coms system. IR is readily radiated by objects in our environment which means that bespite a wave length of about 800nm we can only transmit at a few bits/s or at most half a dozen megabit/s
there is a famious theorem in regards to the amount of information you can transmit in a specified chanel at a particular level of noise, it's called the Shannon Information Capacity Theorem.
C is the maximum capacity of the channel (bits per second), B is the bandwidth of the channel, usualy near enough to some percentage of the carrier, and SNR is the signal to noise ratio.In fact a laser system based solely on the presence or absence of laser wavelengths that are transmitted in free space is an absolutely rotten idea. current photo detectors have no way of "synchronising" to the lased radiation they simple detect the presence or absence of a specific wavelength of light.
because at a fundamental level the shorter the wave length used for transmission the higher the possible rate of transfer is.is the parent thread actually basing his/her post on any information or are they simply trying to pass of there misguided opinions as fact, oh wait this is slash dot...