Why do radios transmit with high frequency signals?

Data link is actually a kind of radio communication, which has two characteristics compared with ordinary radio communication. First, data are represented by binary and 1, that is, digital signals. During transmission, the radio signal will be attenuated. If it is an analog signal, it means that the waveform has changed and there is distortion. In addition, digital signals are easier to encrypt.

second, it adopts standard data format, which can be used and transmitted among many different communication devices, so it is called &; ldquo; Chain & rdquo; . The simple question is to ask the cable to transmit information (transmission includes data, video and sound); Wire transmission uses cables to transmit information, optical fibers, coaxial cables, twisted pairs and so on.

In addition, let me talk about the general principle of wire transmission: the principle of wire electricity technology is that the conductor current changes, and the production line radio waves use the phenomenon that modulation information is loaded on the wire radio waves, and the radio waves propagate in space to the receiving end, which causes the electromagnetic field to change. The conductor current is demodulated and the information current changes are extracted to achieve the purpose of information transmission.

line transmission uses electromagnetic wave transmitter receiver transmitter to generate high-frequency signal oscillator audio signal plus electromagnetic wave modulator high-frequency power amplifier, line transmission space receiver to receive line high-frequency amplifier frequency converter detector audio power amplifier, etc. The original sound of the loudspeaker is transmitted on line, which has exceeded the broadcast communication range, and the electric positioning of the line conductance route is allowed. Since the information to be transmitted is converted into electrical signals, its frequency components are basically in the low-frequency range, there are two insurmountable disadvantages in transmitting these low-frequency electrical signals directly: < P > First, it is non-selective, interferes with each other and cannot realize multi-channel communication.

Second, the frequency of electric signal is low, and the size of wireless antenna is too large.

For this reason, these two shortcomings can be well solved by modulating the carrier wave.

First, high-frequency carrier wave is selected as the signal carrying information, because of its high frequency and small antenna size.

Second, different radio stations can easily realize multi-channel communication by using different carriers.

That's because of the antenna. The size of the antenna is directly related to the working frequency. Wavelength = speed of light/frequency

The higher the frequency and the shorter the wavelength, the smaller the transmitting antenna can be made.

For example, we use a half-wave antenna. Generally, our sound signal is about 2k. If it is not modulated on the carrier frequency but transmitted directly, the size of my antenna is: wavelength /2= light speed/frequency /2=75m.