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Range 1500km at low frequencies long waves.. Sky wave Space wave Frequencies Typically 30 MHz VHF, UHF Range About 80 km above the earth to 500 km Up to 150 km Difficulties The critical

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Lesson 6: Radio

Task 1:

- Light bulb

- Televison

- Oven

- Telephone

- Heater

Task 2:

Table 1

Surface wave Frequencies Low frequencies

Travels Along the ground, following the curvature of the earth’s

surface

Range 1500km at low frequencies (long waves)

Difficulties It’s limited mainly by the extent to which energy is absorbed

from it by the ground

Task 3:

Table 2:

Sky wave Space wave Frequencies Typically 30 MHz VHF, UHF

Range About 80 km above the earth

to 500 km

Up to 150 km

Difficulties The critical frequencies varies

with the time of day and the seasons

Intervening obstacles such as hills, buildings, or trees

Task 4:

1- a: transmitting aerial

2- e: surface wave

3- d: space wave

4- c: sky wave

5- b: receiving aerial

Task 5:

1 When the switch is closed, current flows through the primary of the

transformer

2 On trisking a plane, the radar signal is reflected

3 On discharging quickly, a cell may become hot

4 When reciving signal from the remote control, the TV follows your

instructions

5 When the radar receiver receives the reflected signal, the signal is compared with the transmitted signal

6 When choosing a coures in the electronics, you think carefully about your future

7 On striking a hight building, microwave signals are deflected

8 When making a recording, you should ensure the recording levels are

satisfactory

9 When detecting an intruder, the alarm triggers an audible warning

10 When the remote control button is pressed, the television set changes

channel

Task 7:

Communicate Communicator Communication

Task 9:

1 AF : audio frequency

2 RF : Radio frequency

3 AM : Amplitude modulated

4 FM : Frequency modulated

5

Task 10:

1- D: FM carrier

2- C: AM carrier

3- B: AF signal

4- A: RF carrier

Task 11 :

RF tuner Selects the required RF wave

RF amplifier Amplifies the RF wave

Detector Separates the audio modulation from the

RF carrier wave

AF amplifier Amplifies the audio signal Loudspeaker Converts the audio signal into sound

Task 12 :

- Firstly , the aerial receives weak signal Next , the RF tuner selects the required RF wave from the aerial Following that , the selected RF wave is amplified by the RF amplifier and then passed to the detector , which

separates the audio modulation from the RF carrier wave After that , the audio frequency amplifier amplifies the audio signal to make it strong

enough to drive the loudspeaker Finally , the loudspeaker converts the audio signal into sound

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