(a)[2]
State two changes that happen to a signal as it is transmitted along an optic fibre.
(b(i))[1]
The optic fibre is specified to have an attenuation per unit length of $1.6\,\text{dB km}^{-1}$. The smallest allowable signal-to-noise power ratio in the fibre is $25\,\text{dB}$. The mean noise power in the optic fibre is $6.1 \times 10^{-19}\,\text{W}$. Suggest one reason why power ratios are given in $\text{dB}$.
(b(ii))[5]
The input power to the optic fibre signal is intended to be $6.5\,\text{mW}$. Determine whether repeater amplifiers are needed in the optic fibre between the two towns.