Question 2
-
AIM: To test the knowledge of candidates on fault finding in a radio receiver.
- You are provided with a multichannel radio receiver.
- Connect the radio receiver to the power source.
- Copy Table 2 into your answer booklet.
Table 2
Conditions for tests
Observation
Stations Received
Frequency
Signal strength
with the antenna connected
1
2
3with the antenna disconnected
1
2
3- Switch ON the radio set.
- Set the radio receiver to FM band.
- Tune the radio set to any station in your locality and mark it station 1.
- Note the frequency of the tuned station and record the value in Table 2.
- Search for two other stations by tuning the radio across the band and mark stations 2 and 3.
- Observe and record in Table 2, the signal quality of each station recorded in terms of sensitivity, selectivity and fidelity.
- The supervisor should monitor the activities in steps (k) to (n).
- Switch OFF the radio set and unplug it from the mains.
- Open the back cover of the set.
- Disconnect the antenna connecting wire.
- Re-plug the set and switch it ON.
- Repeat steps (e) to (i).
- Switch OFF the radio and unplug it.
- Compare and comment on the results obtained in Table 2 for steps (i) and (o).
- Identify and state three components on the circuit board.
- State the stages of each identified component in (r).
- The supervisor should reconnect the antenna.
- State two precautions taken when carrying out the activities listed above.
Observation
The expected answers were:
- Correctly copied Table 2.
-
Conditions for tests
Observation
Stations Received
Frequency
Signal strength
with the antenna connected
1
2
3Any three stations
Strong/High
Strong/High
Strong/High
with the antenna disconnected
1
2
3Any three stations
Weak/Low/No signal
Weak/Low/No signal
Weak/Low/No signal
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(q) Reasonable comparison based on information given in Table 2 indicates that the signal strength in the three stations received when antenna was connected is strong while that of the disconnected antenna is weak.
(r) and (s)
|
(r) |
(s) |
|
Components |
Stages |
1 |
Inductor on ferrite rod |
RF amplifier/Local oscillator |
2 |
IF/RF transformer |
RF amplifier/IF amplifier |
3 |
Antenna |
RF amplifier |
4 |
Loudspeaker |
Audio |
5 |
Gang capacitor |
Local oscillator/RF amplifier |
6 |
Resistor |
All stages |
7 |
Transistor |
Rf amplifier/IF amplifier/Audio |
8 |
Integrated circuit |
Audio/Local oscillator |
9 |
Transformer |
RF amplifier/IF amplifier/Power/Audio |
10 |
Diodes |
RF amplifier/IF amplifier/Power/Detector |
(u). Precautions taken
- I ensured the workbench was cleared and free.
- I discharged high voltage capacitors.
- I ensured high voltage live wires were isolated.
- I ensured the right tools for the right jobs.
- I ensured the use of rubber hand gloves.
- I ensured the return of all tools into the tool box.
The candidates in most cases only stated the general functions of components instead of the functions as applied to the purpose for which they were used. Candidates did not show familiarity with the faults associated with radio receiver.