T(a) State the main
                                       (i)        similarity between AM and FM;
                                       (ii)       difference between AM and FM.
(b) State the device that extracts intelligence from the modulated signal in
                                      (i)        AM;
                                      (ii)       FM.
(c) Calculate the wavelength of a radio wave with a frequency of 104.5 MHz.
Take speed of light in vacuum = 3 x 108 m/s
The expected answers were:
                                      (a)       Similarity between AM and FM
A low frequency signal modulates a high frequency carrier
(Any other similarity)
Difference between AM and FM
carrier frequency is modulated in FM, whilst in AM carrier
amplitude is modulated
(Any other difference)
                                      (b)       Device
AM: - Detector (Demodulator)
                                                 FM:     - Discriminator (Demodulator)
                                      (c)       c = fA
c
:.A=-
f
3xl08
=---
104.5xl06
300
=--
104.5
= 2.87 m
The question was on Communication Systems. Many of the candidates in
part (a) referred to the relative merits and demerits of both modulation
types, in part (b), very few candidates knew this while in part (c) most of
320

the candidates that gave incorrect answers wrongly interpreted MHz. The
performance of the candidates was not encouraging.