Electronics Paper 2, Nov/Dec. 2010  
Questions: 1 2 3 4 5 6 7 8 9 10 Main
General Comments

Question 4

(a)Define amplitude modulation.
(b)State the function of the following in an AM superheterodyne receiver:
(i) local oscillator;
(ii) detector.
(c) An AM superheterodyne receiver tuned to frequency of 1600 Hz works at an intermediate frequency of 455 Hz. Calculate its local oscillator frequency.
(d) State the type of modulation used for the sound and video portions respectively in television transmission.


The expected answers were:
(a) AM is the technique in which the amplitude of the carrier signal is varied in accordance with the instantaneous value of the modulation signal.
(b) (i)Local Oscillator
Used to generate a signal (high frequency) to be mixed/ heterodyned with the incoming signal.
(ii) Detector
Used to extract/recover the information signal from the
modulated carrier wave.
(c) Local oscillator freq.{fo)
fo = fs + flF
= 1600KHz + 455KHz
= 2055KHz
(d) (i) Sound fm
(i i) Video am
The question was on Communication Systems. It was not popular with the candidates. The performance was reported below average.

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