调频 调幅 调相(FM PM)

调频调幅调相（FM PM）
Amplitude modulation: a modulated signal that changes the amplitude of a carrier; FM: changes in frequency or phase. Send FM - receive - am: should be received under certain conditions, but the detection efficiency is not necessarily high. For example, the receiver (amplitude modulation) loop can receive the FM signal at a low efficiency when it is in the state of slope detection (referring to radio data).
FM and phase modulation are different, phase modulation at the same time, the frequency will certainly change, but the frequency modulation phase does not necessarily change.
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What is the difference between amplitude and frequency modulation?
1. FM, am, anti-interference ability
Foreign interference, processing and atmospheric interference, influence of modulated wave mainly produce parasitic amplitude modulation, noise. FM system can use amplitude limiting method to eliminate parasitic modulation caused by interference. In amplitude modulation system, the amplitude of the amplitude modulated signal is varied, so that the amplitude limit can not be used, and it is difficult to eliminate the external interference.
In addition, the greater the signal to noise ratio, the stronger the anti-interference ability. The signal-to-noise ratio of
the demodulated signal is related to the modulation coefficient. The greater the modulation coefficient, the greater the signal-to-noise ratio. Because the FM coefficients are much larger than the amplitude modulation coefficients, the FM wave has a high signal-to-noise ratio, and the interference noise in FM broadcasting is small.
2. FM Bobbi amplitude modulation wave frequency bandwidth
The band width is related to the modulation factor, that is, the modulation coefficient is large and the frequency band is wide. The frequency modulation coefficient is often greater than 1, while the amplitude modulation coefficient is less than 1. Therefore, the band width of FM wave is much larger than that of amplitude modulated wave.
3. frequency modulation power utilization is greater than amplitude modulation system
In the total power delivered, the power of the sideband frequency is the effective power of the transmitted modulation signal, while the side frequency power is related to the modulation coefficient, the modulation coefficient is large, and the side frequency power is large. Because the frequency modulation coefficient MF is greater than the amplitude modulation coefficient Ma, the power utilization ratio of the FM system is higher than the amplitude modulation system.
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The difference between FM and am like mobile phone GSM and CDMA,
is a different transmission mode, CDMA technology should I do not know how much advanced than the GSM, but not more than 133 of the mobile phone signal of mobile phone signal 139 strong, but not as good as. Why is the same 139 mobile phone, some manufacturers strong signal, and some manufacturers weak signal? That is to say, a good or bad product is not determined by the mode of transmission, but by the technical ability of the manufacturer and the degree of product completion.
So, is there any difference between FM and am in wireless transmission? No FM is characterized by narrow bandwidth and long distance. Narrow bandwidth means that the penetration capability of the obstruction is weak, but the transmission distance is long. This technology is generally used in mobile phones, pagers and other needs of long distance (5 kilometers or more) transmission products. Readers should know that Mobile Corporation's signal towers are far removed from each person's mobile phones. Amplitude modulation is characterized by wide bandwidth and short distance. Wide bandwidth means that the penetration of the barrier is strong, but the transmission distance is shorter. This technology is generally used in wireless alarm, wireless security and other fields. For in a house the most important thing is not the distance, but the penetrating power.
So, FM technology is advanced,
Is the technique of amplitude modulation behind? No The Federal Communications Commission (FM) introduced FM and am technology since the last century and has been used in all our living areas. FM and am are just different transmission methods for a wireless
technician, and there is no technical difficulty.
Is there any difference between FM and am? Neither！ There are many differences, one of which is the cost. Because the frequency modulation line is more complex, needs the component quantity to be many, therefore the frequency modulation product's price must compare the banner product the price to be much higher. Why do most domestic wireless call system manufacturers adopt amplitude modulation mode? First of all, the transmission in the building does not need to use high cost FM to do, as long as the scroll products to improve the degree of completion, to fully solve the transmission distance and coverage area. As an agent, the same product shape, the same distance effect, different price, which one would you choose? In fact, plainly, customers do not need to know the frequency modulation or amplitude modulation, inexpensive, economical and practical products is the truth.
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Widely used in military, communications, radio, television, radio and other fields
What are frequency modulation (FM), amplitude modulation (AM), short wave (SW) and long wave (LW)?
Both AM and FM band in general radio or radiocassette, I believe we are already familiar with, the two band is used for you to listen to the radio broadcast home, if there SW band, so in addition to domestic shortwave radio, you can listen to the world broadcast radio program. In order for you to have a better
understanding of the use of radio, what follows is a brief description of what AM, FM, SW, and LW are.
In fact, "AM" and "FM" refer to two different modulations in wireless electrical engineering. The AM: Amplitude Modulation is called amplitude modulation, while the FM: Frequency Modulation is called fm. Just MW: Medium Wave (general radio broadcasting), using the amplitude modulation (AM) way, unconsciously, between MW and AM on an equal sign. In fact, MW is just a lot of using a broadcast AM modulation, as in a high frequency (3-30MHz) modulation methods used in the International Shortwave Radio is AM, even higher frequency than the FM radio navigation communication (116-136MHz) is AM, AM band is our daily said that Poland broadcast (MW).
What about FM? It is similar to the fate of MW. We used FM to refer to the general FM radio (76-108MHz, in China for
87.5-108MHz, Japan 76-90MHz), the fact that FM is a kind of modulation, even in the short wave range 27-30MHz, as amateur radio, satellite communications, space applications band, but also the use of frequency modulation (FM) mode the.
And what about SW? In fact, can be said to be short wave of a simple name, the correct statement should be high frequency (HF:High Frequency) more appropriate. And how does the name "shortwave" come from? At wavelengths, the medium wave (MW) is between 200-600 meters (meters), while the wavelength of HF is between 10~100 meters (meters). Compared with the wave appearance, the wavelength of HF is really shorter,
因此就把hf称做短波 (sw: short wave).
同样的, 比中波mw更低频率的150khz - 284khz之间的这一段频谱也是作为广播用的, 以波长而言, 它大约在1000～2000米 (公尺) 之间, 和mw的200 - 600米相比较显然 "长" 多了, 因此就把这段频谱的广播称做长波 (lw: long wave).实际上, 不论长波 (lw) 、中波 (mw) 或者是短波 (sw) 都是采用am调制方式.
对一般收 (录) 音机而言, fm、mw、lw波段是提供您收听国内广播用的, 但我国目前没有设立lw电台, 而sw波段则主要供您收听国内/ 国际远距离广播.
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短波知识
百年前, 三声短促而且微弱的讯号, 向世界宣布了无线电的诞生.一九? 一年, 扎营守候在讯号山 (signal hill位于加拿大东南角) 的意大利科学家马可尼, 终于接收到了从英格兰发出的跨过大西洋的无线电讯号, 这个实验向世人证明了无线电再也不是仅限于实验室的新奇东西, 而是一种实用的通讯媒介.此后短波用作全球性的国际通讯媒介便开始发达起来了.
虽然马可尼的试验结果令人相当振奋, 可是当时一般人认为无线电传播方式类似光波, 发射之后, 绝对沿直线方向进行传播, 从英国到加拿大, 再怎么说也无法完成直线的无线电通讯 (因为地球表面是弧形的).当时的科学理论更证明, 从英国发射后的无线电波一定直驱太空, 怎么可能到达加拿大? 可是从马可尼用简陋的无线电设备征服长距离通讯的试验记录来看, 白天, 讯号可以远达700英哩, 晚间更远达2000英哩以上, 这些试验数据, 使得以往的理论所推断出来的必然结果, 开始发生动摇了.
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使载波振幅按照调制信号改变的调制方式叫调幅.经过调幅的电波叫调幅波.它保持着高频载波的频率特性, 但包络线的形状则和信号波形相似.调幅波的振幅大小, 由调制信号的强度决定.调幅波用英文
字母am表示.
使载波频率按照调制信号改变的调制方式叫调频.已调波频率变化的大小由调制信号的大小决定, 变化的周期由调制信号的频率决定.已调波的振幅保持不变.调频波的波形, 就像是个被压缩得不均匀的弹簧, 调频波用英文字母fm表示.
目前, 中波广播使用的频段大致为550khz - 1600khz, 主要靠地波传播, 也伴有部分天波; 调频制无线电广播多用超短波 (甚高频)
无线电波传送信号, 使用频率约为88mhz - 108mhz, 主要靠空间波传送信号.
使载波振幅按照调制信号改变的调制方式叫调幅.经过调幅的电波叫调幅波
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
调制又分为三种: 调幅, 调频和调相.
The amplitude modulation is represented by AM, the FM is represented by FM, and the phase modulation is expressed by PM. This is where we can find the AM.FM sign when we listen to the broadcast.
Its basic principle is that the modulated signal to be
transmitted (here we use the voice signal as an example) from low frequency to high frequency shifting, so that it can be transmitted through the ionosphere reflection in the remote receiver we use proper demodulation device then restore the original signal without distortion, to transmit voice frequency signal the purpose of.
For example, am, we cannot directly transfer the voice, we first use a voice signal conversion device (or say) is converted into voltage signal amplitude changes smoothly, this is our signal to be transmitted, called modulation signal, and then the modulation signal and a high frequency signal in a multiplier, after an adder circuit, get a signal of high frequency, its envelope (the so-called envelope is connected with periodic signal in each cycle peak of the imaginary line) varies with the amplitude of modulation signal, we put the high frequency signal is called the carrier, the signal has been modulated called amplitude modulation wave.
That is to say, the voice signals we are transmitting are already included in the AM wave, in other words, we move the modulation signal from low frequency to high frequency to facilitate ionospheric propagation. So we will adjust the signal transmitting device through the launch at the receiver after receiving the signal, the demodulation device to recover the original signal after conversion device voltage signal recovery in adult Mandarin, is implemented between two of two people to call, which is the basic principle of shortwave radio.
We look at FM, with the above knowledge base, we can understand the principle of FM, FM, is the frequency of the carrier with
the voice signal (amplitude modulated signal) changes the voice signal amplitude, the frequency of the carrier is increased, the voice signal amplitude is small, the frequency of the carrier is reduced accordingly note that, here is a change in the frequency but not amplitude, this is the difference between frequency and amplitude, we modulated, had a frequency change with the change of the modulation signal modulated signal, we call "FM signal".
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Generally speaking, FM refers to 64---108MHz, that is, ultrashort wave, suitable for city high fidelity short distance broadcast, generally within 100 kilometers
Generally speaking, FM refers to 64---108MHz, that is, ultrashort wave, suitable for city high fidelity short distance broadcast, generally within 100 kilometers
Amplitude modulation is medium wave, the range is 503---1060KHz, and the distance is far away, which is greatly affected by weather factors. It is suitable for the broadcast of inter provincial radio station.
Amplitude modulation is medium wave, the range is 503---1060KHz, and the distance is far away, which is greatly affected by weather factors. It is suitable for the broadcast of inter provincial radio station.。