How "Radio and Television" conveys information—Introduction to communication technology PPT courseware 5

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How "Radio and Television" conveys information—Introduction to communication technology PPT courseware 5

Think about it:

Electromagnetic waves are generated by changing currents. When you turn on a fluorescent lamp, you will hear noise in a nearby radio. This noise is caused by the intermittent current formed when the circuit is on and off, which excites electromagnetic waves in the surrounding space and is received by the radio.

do you know?

Today, with the rapid development of information technology, electromagnetic waves are becoming more and more important to us. Radio and television must use electromagnetic waves, radio communications must use electromagnetic waves, and automatic control and communication in aviation and aerospace must use electromagnetic waves...

Since electromagnetic waves have different frequencies and wavelengths, their uses are also different. Electromagnetic waves are used for radio, television and mobile communications. With radio and television, the myths of "clairvoyance" and "sound ears" in ancient Chinese legends have become facts. So how to use electromagnetic waves to transmit sounds and images?

Compare: Flying pigeons to deliver messages - using pigeons to deliver messages.

Pigeons are the "carriers" of information

Radio, television, communications

--Using electromagnetic waves as "carriers" to transmit information

The process of transmitting electromagnetic waves

(1) High-frequency oscillation current is generated by a high-frequency oscillator

(2) Convert the sound and image signals to be transmitted into current signals (electrical signals)

(3) Input the high-frequency oscillation current generated by the oscillator and the signal current of sound and image into the modulator, so that the high-frequency oscillation current changes correspondingly with the transmitted sound and image signal, and then the high-frequency oscillation current is The current is sent to the transmitting antenna, and the emitted electromagnetic wave carries the sound and image signal to be transmitted. That is, the so-called "adding" the signal to be transmitted to the electromagnetic wave. The electromagnetic wave with the signal is emitted.

radio reception process

(1) Use an antenna to receive electromagnetic waves.

(2) Use a tuner, that is, a circuit for selecting channels in a radio or television, to select the required electrical signal.

(3) By letting the high-frequency oscillating current pass through the detector, the sound signal and image signal to be transmitted can be "detected" from the high-frequency oscillating current. By sending the sound signal and image signal to the speaker and the TV respectively, you can hear the sound and see the image.

mobile phone

1. Working principle: A mobile phone is equivalent to a radio station. It converts the user's voice into high-frequency electrical signals and transmits them into the air. At the same time, it captures electromagnetic waves in the air, allowing the user to receive information from the other party.

2. Reasons for setting up base stations: Handheld mobile phones are small in size and have low transmitting power; their antennas are also very simple and have low sensitivity. Therefore, its calls to other users must be relayed through larger fixed base stations.

mobile communications

1. Mobile phones use _____ to transmit sound, which is both _________ and _____.

2. Mobile phones rely on ________ (larger fixed radio stations) to allow people in different places to talk to each other.

Reasons for setting up base stations: mobile phones are small in size, have low transmitting power, simple antennas, and low sensitivity.

Cordless phone: There is no telephone line connecting the host and the mobile phone. They rely on radio waves to communicate. The host is connected to the local telephone network and is equivalent to a small base station.

The mobile phone cannot be too far away from the host computer.

1. Regarding mobile phones, which of the following statements is incorrect ( )

A. The sound signal in a mobile phone is transmitted by current in the wire

B． The sound signals in mobile phones are transmitted by electromagnetic waves in space

C. Mobile phones are both radio transmitters and radio receivers

D． Calls between mobile phones are relayed by base stations

2. The electromagnetic waves emitted from the radio station are ( )

A. High frequency electromagnetic waves generated by oscillators

B． Low-frequency electromagnetic waves that change with sound

C. High-frequency electromagnetic waves modulated by sound signals

D． High-frequency electromagnetic waves modulated by image signals

3． When listening to radio broadcasts on the radio, the person in the radio who is responsible for selecting the station is ( )

A. Receiving antenna B. Tuner c. Detector D. speaker

The transmission process of radio broadcasting is: the microphone of the radio station converts the announcer's ________ into ________, then uses a modulator to load the audio electrical signal onto __________ (carrier wave), and then transmits it out through the antenna; the reception of radio broadcasting The process is: the antenna of the radio receives various ________. By turning the knob of the radio tuner, the ________ signal can be selected from it. The electronic circuit in the radio then takes out the ________ signal, amplifies it and sends it Convert it to ________ in the speaker, and we can hear the broadcast.

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Update Time: 2024-11-22

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