ANSWERS: 5

Particularly in an AM radio system increased bandwidth increases noise and decreases the signal to noise ratio. For the mathematical version (including Boltzmann's constant etc.) see http://www.veron.nl/amrad/art/sysnoise.pdf

maybe when u have a high bandwidth u get more noise power..that is just a guess

Hmm....I'm not seeing exactly either of these answers. From what I see noise in a system limits the ceiling on bandwidth. X amount of noise allows up to X amount of bandwidth whereas less than X amount of noise in a system means increased bandwidth is possible (over X). http://www.cs.ucl.ac.uk/staff/S.Bhatti/D51notes/node6.html

Noise power in Watts = k x T x dF k = some kind of constant (Boltzman, I think but don't take my word for it  I can't find my electronics book, dammit!) T = temperature in Kelvin dF = delta F = bandwidth in Hertz (is it about time that computer keyboards got a 'delta' key?) Therefore, if, for example, you double the bandwidth, you'll double the noise power. Coming to think of it, I think that only applies to 'white noise'. You may find other types of noise that behave differently.

In the USA, the FCC (Federal Communications Commission) states that bandwidth, is a sustained signal which is 26 dB above the common noise floor.
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