Question 6
(a) Explain the function of the following stages in an amplitude modulation superhet radio
Receiver:
(i) mixer;
(ii) automatic gain;
(iii) detector.
(b) State the frequency of the following in PAL television system receivers:
(i) horizontal oscillators;
(ii) vertical oscillators.
The expected answers were:
(a) In an AM superhet receiver
(i) Mixer: processes input received radio frequency and local carrier frequency to produce the intermediate frequency as its output.
(ii) Automatic Gain Control: enables the control of receiver gain in order to stabilize the audio frequency output and prevent overloading
(iii) Detector: demodulates the amplitude modulated carrier to recover the message signal
(b) In PAL TV standards the frequency of the:
(i) horizontal oscillator is 15625Hz or 15.625kHz;
(ii) vertical oscillatoris 50Hz.
The Chief Examiner reported that, despite the recall nature of this question, majority of the candidates that attempted it did not respond well. It was further reported that, some candidates stated types of oscillators instead of the frequency of horizontal and vertical oscillators in PAL TV standards as demanded.