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When you send some kind of radio signals at some frequency say 5 GHz to a repeater and it transmits it back at higher power, what change is made to the radio signal? For example: Will it be transmitted back at higher frequency or in what terms it is said to be amplified? How do you measure its strength?

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-1, not physics, general reference. –  user2963 Jan 17 '12 at 13:59

2 Answers 2

All electromagnetic signals that leave an antenna have an amplitude, i.e. there is power propagating as they spread.

power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit time.

The signal which the waves are carrying is a pattern on this propagation of energy. As energy is transmitted from the original antenna, the power falls as 1/r^2, so, as the distance grows the signal also becomes weaker in strength/energy, smaller in amplitude.

A repeater boosts the power once more, keeping the signal shape on the electromagnetic carrier wave but restoring the amplitude to levels detectable by radio/tv/mobiles...

The frequency pattern is kept unchanged because it is the one carrying the message and the tunability.

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Anna, in the real world, don't repeaters usually transmit on a different frequency, so that you don't get an interference pattern between the repeater and the original signal? –  Harry Johnston Jan 17 '12 at 22:34
    
as there is a blackout or white out (PIPA SOPA) on many sites I cannot research this on the web. Frequency modulation (FM) would probably not suffer from this as already it is modulating frequencies about the carrier frequency. I suppose that for AM a repeater would be used where the incoming signal would be so small that it would not make a difference to the amplified one. Otherwise the tuning frequency would change and it is a necessary hallmark of the stations. –  anna v Jan 18 '12 at 5:56
    
In New Zealand at least, each TV station is on different frequencies in different parts of the country - but I'm not sure about radio, now that I think of it. –  Harry Johnston Jan 18 '12 at 22:18
    
@Harry Johnston You are correct about TV, they do change the channel number. Possibly there are greater demands for a clear image, or harder to filter noise and reproduce. Once the black out is gone I will do a search. –  anna v Jan 19 '12 at 4:49
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Here is what wikipedia says about repeaters en.wikipedia.org/wiki/Repeaters . It seems to me that it is up to the specific situation on whether the frequency is changed or not. –  anna v Jan 19 '12 at 6:58

This is basically the same as Anna's answer but worded differently;

A radio wave is characterised by two parameters, it's frequency and it's amplitude. The amplitude is the "strength" of the wave i.e. if you connect a multimeter to an aerial then the greater the wave amplitude is, the stronger will be the voltage you measure on your multimeter.

So a repeater just retransmits the signal at the same frequency but with the amplitude multiplied by some factor. The more powerful the repeater the more it multiplies the strength of the signal.

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