Telephone signals may be transmitted either by means of an optic fibre or by means of a wire pair. State three advantages of the use of an optic fibre rather than a wire pair.
It is proposed to transmit a signal over a distance of 
by means of an optic fibre. The input signal has a power of 
. The minimum signal that can be detected at the output has a power of 
. For this signal power, the signal-to-noise ratio is 
. Calculate:
the power of the background noise
the maximum attenuation per unit length of the optic fibre that allows for uninterrupted transmission of the signal.
.
.
