Read and translate the text. Use the dictionary if you need.

AM broadcast radio sends music and voice in the Medium Frequency (MF—0.300 MHz to 3 MHz) radio spectrum. AM radio uses amplitude modulation, in which the amplitude of the transmitted signal is made proportional to the sound amplitude captured (transduced) by the microphone while the transmitted frequency remains unchanged. Transmissions are affected by static and interference because lightning and other sources of radio that are transmitting at the same frequency add their amplitudes to the original transmitted amplitude.

FM broadcast radio sends music and voice with higher fidelity than AM radio. In frequency modulation, amplitude variation at the microphone cause the transmitter frequency to fluctuate. Because the audio signal modulates the frequency and not the amplitude, an FM signal is not subject to static and interference in the same way as AM signals. FM is transmitted in the Very High Frequency (VHF—30 MHz to 300 MHz) radio spectrum. VHF radio waves act more like light, travelling in straight lines, hence the reception range is generally limited to about 50-100 miles. During unusual upper atmospheric conditions, FM signals are occasionally reflected back towards the Earth by the ionosphere, resulting in Long distance FM reception. FM receivers are subject to the capture effect, which causes the radio to only receive the strongest signal when multiple signals appear on the same frequency. FM receivers are relatively immune to lightning and spark interference.

FM subcarrier services are secondary signals transmitted "piggyback" along with the main program. Special receivers are required to utilize these services. Analog channels may contain alternative programming, such as reading services for the blind, background music or stereo sound signals. In some extremely crowded metropolitan areas, the subchannel program might be an alternate foreign language radio program for various ethnic groups. Subcarriers can also transmit digital data, such as station identification, the current song's name, web addresses, or stock quotes. In some countries, FM radios automatically retune themselves to the same channel in a different district by using sub-bands.

EXERCISE EXERCISE2

Make up questions to the answers below

1.Q:______________________ ?

A: MF—0.300 MHz to 3 MHz

2.Q:__How ________amplitude and ________change?

A: The amplitude of the transmitted signal is made proportional to the sound amplitude captured (transduced) by the microphone while the transmitted frequency remains unchanged.

3.Q: What_________________affected ___?

A: Transmissions are affected by static and interference.

4.Q: ___________________________?

A: AM is transmitted in the Medium Frequency but FM is transmitted in the Very High Frequency

5.Q:____________________________?

A: 30 MHz to 300 MHz.

6. Q:___________________________?

A: to lightning and spark interference.

7.Q:___________________________?

A: They are secondary signals transmitted "piggyback" along with the main program.

EXERCISE 3

Work in pairs. Choose between the topics ‘AM broadcast radio’ and ‘FM broadcast radio’. Exchange information addressing to your partner, ask questions and get answers.

UNIT VI

AMPLIFIERS

Text I

What do we call Amplifiers

EXERCISE 1

Practice saying some words from this unit and put them in the right stress pattern box.

Terminal	Heterodyne	Demodulator	Fluctuation
apparatus	Relation	Therefore	Output
Intermediate	compression	Amplitude	Professional
frequency	controlling	transceiving	decameter