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Theme: Crystal Radio Set
Task 1. Read the text.
Task 2. Find answers to the questions in the text:
1. Which device produces high-frequency energy?
2. Which device receives radio waves?
3. What necessary components has radio?
4. What are the parts of a transmitter?
Radio waves start traveling when a transmitter sends out a constant amplitude signal at a very high frequency. Radio waves are traveling but the transmitter makes no sound.
A microphone is connected to the circuit of the transmitting antenna. When we speak into the microphone its resistance varies with the audio frequency. An alternating current is established in the microphone and antenna circuits and its frequency is the same as the audio frequency. Oscillations of the same frequency are induced in the antenna and in the oscillatory circuit of a receiver. These oscillations are in fact a high-frequency current.
In order to reproduce the transmitted sound, this current modulated by audio frequency should be sent through a telephone. The high-frequency alternating current cannot pass through the telephone coils. In order to reproduce the transmitted sounds, a detector or rectifier should be connected to the telephone circuit. It passes (lie current only in one direction. Therefore the current in the rectifier and telephone circuits will not be alternating current but rectified current.
The audio frequency rectified current passes through the telephone and produces oscillations. These oscillations will reproduce the sounds produced at the transmitting stations.
The device called a crystal radio set uses the energy induced in the receiving antenna. Its operation will be the better, the more energy is received by its oscillatory circuit. The oscillatory circuit is also provided with a ground. It is important for good operation of the receiver. The antenna should be grounded by means of a switch.
Practice the following words from the text:
audio - звуковой, низкий rectifier - выпрямитель
alternating - переменный to rectify - выпрямитель
to establish – устанавливать the... the - чем...тем
in order to - для того чтобы
Task 3. Read and translate the following word combinations:
Direct and alternating current; rectified current; audio frequency rectified
Current; constant amplitude signal; radio set operation.
Task 4. Complete the sentences:
Current in the rectifier...
— is not alternating current.
— is rectified current.
— is audio frequency rectified current.
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| Task 7. Read the Text. The clockwork radio | | | Практическое занятие № 5 |