(a)[3]
State three advantages of using an optic fibre instead of a wire pair.
(b(i))[2]
A signal is proposed to be sent across a distance of $4.5 \times 10^{3}\,\text{km}$ using an optic fibre. The input signal power is $9.8\,\text{mW}$. The smallest signal detectable at the output has a power of $6.3 \times 10^{-17}\,\text{W}$. For this signal power, the signal-to-noise ratio is $21\,\text{dB}$. Calculate the power of the background noise.
(b(ii))[2]
Calculate the greatest attenuation per unit length of the optic fibre that still permits uninterrupted transmission of the signal.