Question 6
Figure 4 is a block diagram of an AM broadcasting sub-system.
(i) Name the sub-system represented in Figure 4.
(ii) State two reasons for your answer in 6(a)(i).
(iii) Identify the blocks marked P, Q and R.
(b) State two:
(i) stages common to both superheterodyne and tuned frequency radio receivers;
(ii) advantages of superheterodyne radio receiver over tuned radio frequency receiver.
The expected answers were:
(i) The AM broadcasting subsystem shown in Fig. 4 is a transmitter
(ii) Reasons for answer in (a)i
- Presence of microphone
- Presence of modulator
- Position or location of antenna
(iii) P – AF amplifier
Q – RF oscillator
R – Power amplifier / RF power amplifier
(b) (i) Stages common to both superheterodyne and tuned frequency radio receivers
RF amplifier, AF amplifier, Antenna, Loud speaker
(ii) Advantages of superheterodyne radio receiver over tuned radio frequency receiver
- It is easier to filter
- It offers better sensitivity
- Improved stability
- Improved gain
- Better fidelity
- Prevents image noise fold-over due to use of two IF frequencies before conversion to baseband
The tasks in this question require a higher level of thinking despite being well featured in past examinations as it was presented in a different manner. The Chief Examiner reported that, majority of the candidates that attempted this question did not give the correct response.
(ii) Types of sensors
- Temperature sensor
- Acoustic/sound sensor
- Proximity sensor
- Capacitive sensor
- Pressure sensor
- Smoke sensor
- Light sensor
(b) X – antenna
Y – detector
Z – speaker
It was reported that candidates responded very well to question 6 but a few were unable to identify superheterodyne blocks in part (b).