What is the role of the modulation of the radio?

The principle of radio is to restore the high-frequency signal received from the antenna into an audio signal through detection (demodulation), and send it to the headset to become a sound wave. Due to the development of broadcasting, there are a lot of radio waves of different frequencies in the sky. If you pick up all these radio waves, the audio signal will be as if you are in a busy city, and many sounds will be mixed together, and as a result, you will not be able to hear anything clearly.

In order to try to select the desired program, after receiving the antenna, there is a selective circuit, its function is to pick out the required signal (station), and "filter out" the unwanted signal to avoid interference, which is the "select station" button used when we listen to the radio. The output of the selective circuit is to select the high-frequency amplitude modulation signal of a certain station, and it is not possible to use it to directly push the headphone (electro-acoustic device), but also to restore it to the original audio signal, this reduction circuit is called demodulation, and the demodulated audio signal is sent to the earphone, and the broadcast can be received. The simplest radio mentioned above is called a direct detector, but the high-frequency antenna electrical signal obtained from the receiving antenna is generally very weak, and it is not suitable to send it directly to the detector, so it is best to insert a high-frequency amplifier between the selection circuit and the detector to amplify the high-frequency signal.

Even if a high-frequency amplifier has been added, the power of the detector output is usually only a few milliwatts, and it is okay to listen to it with headphones, but it is too small to use a speaker, so an audio amplifier is added after the detector output to push the speaker. High-amplification radios are more sensitive and powerful than direct detection radios, but they are less selective and more complex to tune. The high-frequency signal received from the antenna is amplified hundreds or even tens of thousands of times, generally there are several levels of high-frequency amplification, each stage circuit has a resonant circuit, when the frequency is changed, the resonant circuit has to be readjusted, and the selectivity and passband after each adjustment are difficult to ensure that exactly the same, in order to overcome these shortcomings, the current radio almost all use superheterodyne circuits.

The characteristics of superheterodyne are: the carrier frequency of the selected high-frequency signal becomes a lower fixed intermediate frequency (465kHz), and then the intermediate frequency amplifier is used to amplify it to meet the requirements of detection, and then the detection is carried out. In the superheterodyne receiver, in order to produce frequency conversion, there is also an external sinusoidal signal, which is usually called heterodyne signal, and the circuit that produces heterodyne signal is used to be called local oscillation.

The frequency of the radio and the frequency of the received signal are one IF difference, so the selection circuit before the mixer and the local oscillator are tuned with a unified tuning line, such as a coaxial double capacitor (PVC), so that the difference is kept at a fixed IF value. Because the intermediate frequency is fixed, and the frequency is lower than the high-frequency modulated signal, the gain of the intermediate amplification can be larger, the work is more stable, and the passband characteristics can also be more ideal, so that the detector can obtain a large enough signal, so that the whole machine can output a better audio signal with better sound quality.

If you want to transmit a signal, the signal has to be a high-frequency signal, and the low-frequency signal can't travel far, and we have to turn it into a high-frequency signal first, then this process is called modulation.

It's the signal, which is FM FM. It's like a mobile phone, how can you play without a signal!

1. Difference: The difference between frequency modulation (FM) and amplitude modulation (AM) of radio is that the radio wave modulation method is different, frequency modulation is a modulation method that represents information based on the instantaneous frequency change of the carrier, and amplitude modulation is a modulation method that changes the amplitude of the carrier wave with the signal.

2. Frequency modulation, the full name is "frequency modulation". A modulation method that makes the instantaneous frequency of the carrier wave change according to the change law of the desired transmitted signal. It is a modulation method that causes the instantaneous frequency of the modulated wave to change with the modulated signal.

The electric attack method to realize this modulation method is called frequency modulator, which is widely used in FM radio, television accompaniment, microwave communication, phase-locked circuit and frequency sweeper. The basic requirements for the frequency modulator are large frequency modulation shift, good frequency modulation characteristics, and small parasitic amplitude modulation.

The radio waves generated by the frequency modulation method are called frequency modulation waves, and their basic characteristics are that the oscillation amplitude of the carrier remains unchanged, and the oscillation frequency changes with the modulation signal. Frequency modulation (FM) means that the frequency of the high-frequency carrier is not a constant, but a modulation method that changes within a certain range with the modulated signal, and its amplitude is a constant. On the other hand, amplitude modulation means that the frequency of the carrier frequency is constant, and its amplitude varies with the modulated signal.

3. Amplitude modulation, amplitude modulation (AM). Amplitude modulation, also known as medium wave, ranges from 530---1600kHz. Amplitude modulation is an electrical signal that changes the amplitude by the high and low beats of the sound.

The transmission distance is far away, but it is greatly affected by weather factors, which is suitable for the broadcast of inter-provincial radio. In the early VHF band, most of the mobile communication stations used amplitude modulation, because the channel fading will cause the analog amplitude modulation to produce additional amplitude modulation, resulting in distortion, and it is easy to be eavesdropped in the process of transmission, so it is rarely used at present. At present, it is still used in simple communication equipment, such as the AM band in the radio is the amplitude modulation wave, and the sound quality is inferior compared with the FM band FM wave.

Introduction: Today's era is the era of science and technology, and many electrical functions have been replaced by mobile phones and computers, but despite this, the value of their own existence is indeed something that we cannot ignore. For example, the radio, although the cash register also has its function, it also has irreplaceable value for people.

There are many types of radios, among which FM radio is more popular, so what is FM radio? How does FM radio work? Let's find out together.

FM Radio — Introduction

FM radio is the modulation method in which the carrier frequency changes according to the modulation Xinhai. The FM radio has been commissioned. The magnitude of the frequency change is determined by the modulated signal, and the period of its change is also determined by the frequency of the modulated signal.

The amplitude of the already tuned wave remains the same. In FM radio, FM waves are represented in English FM. In general, an FM radio is a type of radio that can receive FM radio programs.

FM radio — featured

FM radio supports the search of various contents such as technology, literature, **, news, current affairs, comedy, etc., and it contains rich content; In addition, the FM radio also supports channel search between frequencies, and the search range is very wide, so that the received information has become wide and numerous; At the same time, the FM radio can also scan the pump to save the station, which is convenient for the next time it can be directly turned on and used; When using a variable frequency radio, you must plug in the headphones first, otherwise you will not be able to open any programs.

FM Radio—Principle Analysis

In order for the FM radio to work normally, it must receive the radio waves with the frequency response of the debugging, and then obtain the information modulated on it from the radio waves, and after receiving the high-frequency radio waves of the radio station that we need to listen to, then the radio wave information is carried, and the process of carrying this is called debugging, and the action of removing the sound signal is called demodulation. The sound information demodulated from the radio waves is an electrical signal with a very low amplitude at the beginning, and the human ear cannot hear it, so it is necessary to use a power amplification circuit to increase its amplitude, and it can be transmitted to the human ear through the speaker and horn.

FM radio — advantages

As one of the more popular FM radios, its own advantages can not be ignored, first of all, FM radio anti-interference can be strong, can receive radio wave information without interference, and the noise is low, the sound is very clear and clean; In addition, the frequency bandwidth and sound quality of FM radio are three-dimensional, and the design effect is better; Of course, the biggest advantage of FM radio is that it has a large number of available FM, more acceptable stations, and more sound information obtained by users.

FM radio - malfunction

There are three main faults of the FM radio we use, one is that the radio station cannot be received; the second is low sensitivity; The third is that it is noisy; First of all, the failure to receive the radio may be due to the local oscillator and the suspension of the vibration, which cannot generate the signal; The low sensitivity is most likely due to the failure of the pad capacitor; The reason for the high noise is generally that the penetration current of the inverter tube is too large or the performance is not good. For different faults, different methods are adopted for repair.

An FM radio is an electronic device that receives sound broadcasts, and it uses FM technology to receive FM broadcasts. FM broadcasting uses a technique called frequency modulation, that is, the audio signal is converted into a high-frequency signal, and then the high-frequency signal is added to the carrier for transmission. The working mode of FM radio is to receive the modulated Gaodan Mengsun frequency signal and demodulate it into the original audio signal.

Specifically, its workflow is as follows:1The antenna receives the electromagnetic wave signal and converts it into an electrical signal to send to the radio.

2.The radio boosts the signal through an RF amplifier and converts it into an intermediate frequency signal. 3.

The IF signal is mixed with a local oscillator through the mixer mode chain to obtain a new signal, which is then amplified by the IF amplifier. 4.The IF signal is demodulated by a demodulator to obtain the original audio signal, which is amplified by an audio amplifier and finally outputs sound through the speaker.

One of the key steps in the above process is demodulation, which is the process of restoring the modulated high-frequency signal into the original audio signal. There are generally two demodulation methods in a demodulator: one is frequency discrimination demodulation, and the other is amplitude discrimination demodulation.

Frequency discrimination demodulation is to restore the audio signal by identifying the change in carrier frequency; Amplitude detection demodulation restores the audio signal by identifying changes in the amplitude of the carrier.