"Radio and Television" How to Transmit Information—Introduction to Communication Technology PPT Courseware 2

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"Radio and Television" How to Transmit Information—Introduction to Communication Technology PPT Courseware 2

1. Audio, video and radio frequency signal modulation

1. The principle of electromagnetic waves transmitting sound and image signals

Electromagnetic waves carry sound and image signals just like pigeons carry messages.

First, the signal is carried on the electromagnetic wave, and then the electromagnetic wave carrying the signal is emitted, and when it reaches the receiving location, the signal is detected from the electromagnetic wave.

2. The emission process of electromagnetic waves

(1) A high-frequency oscillation current---radio frequency signal is generated by a high-frequency oscillator.

(2) Convert the sound---audio signal and image---video signal to be transmitted into a current signal (electrical signal)

(3) Input the high-frequency oscillation current generated by the oscillator and the signal current of sound and image into the modulator - modulation, so that the high-frequency oscillation current changes accordingly with the transmitted sound and image signal, and then the The high-frequency oscillating 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.

2. Transmission and reception of radio broadcasts

1. The transmission process of radio broadcasting

2. Radio reception process

(1) Use an antenna to receive electromagnetic waves.

(2) Use a tuner, which is the channel selection circuit 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, Hear sounds and see images.

During extracurricular activities, several students discussed the reception and transmission of radio broadcasts and television signals. They made the following statements. Which one do you think is correct? ( )

A. Radio broadcasting is the mutual conversion between optical and electrical signals.

B. The reception or emission of television signals is the conversion between acoustic and electrical signals.

C. Both radio broadcasting and television are the conversion of light and electrical signals.

D. Whether it is radio broadcasting or television, there is conversion of sound and electrical signals.

Analog and digital signals

Analog signal: The frequency and amplitude of the current all "imitate" changes in the frequency and amplitude of the sound.

Digital signal: Text, sound, and images are all encoded with binary numbers "0" and "1".

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Update Time: 2024-08-31

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