Basic knowledge of analog signals in telecommunication systems In analog communication systems, the original signal (in this case, sound) is directly converted into an electrical signal. The characteristics of an analog signal are related to two constant variables: the amplitude and frequency of the signal. The strength (amplitude) of the electrical signal changes with the size of the sound, and the frequency of the electrical signal changes with the sound quality or pitch. The change of the two variables (amplitude and frequency) is proportional to the original sound wave. A more vivid example is the visual display of some Ditu high schools. The light display can reflect music and change with the music. In analog communication systems, electrical signals (not light) are constantly changing. The lights of the disco playing equipment change and flash with the beat of the music. Here, the light changes with the electrical characteristics of the signal. In telecommunications terminology, it can be said that the real sound is produced by impact sound waves. The impact of this sound wave is actually the movement of air molecules. The technical term is called compression and expansion. Human voice is a very special thing. When we speak we will produce sound. In a relatively short period of time, we actually hit the air waves together many times. for example. First generate a simulated sine wave, and then convert it into electrical equivalent. Very simple, if you can get the sound generated by the voice and modify it based on the sound quality and intensity, you can get this sine wave. If you use a magnetic field to convert the sound into electricity, this waveform will be generated. Rotate the current 360 "around the zero-voltage reference line. The 360o waveform around the zero line is called an HZ-named after the electrical engineer who specified the concept. The waveform starts at the zero line and follows the energy It increases and rises, and finally falls after reaching a peak; the energy will also fall from this height to the zero line, and continue to fall on the zero line. Until the point below the zero line (this is called the negative side of the waveform). Continue After reaching the peak voltage on this side, the energy will also reach the peak and start to rise back to the zero line. The waveform completes a complete cycle of 360o, and a complete cycle constitutes a HZ. The human vocal cords can strike sound waves together at 100 to 5000 times per second. In short, vocals can produce up to 5000 cycles per second. When converted into electrical equivalent, there is 5000HZ. In order to avoid trouble, it can be abbreviated as 5kHZ (meaning "dry"). With the electrical equivalent, we have an analogy or simulation of sound waves. This is a constantly changing value or electrical energy. The amplitude and frequency will change 100 to 5000 times per second. This is what the telephone company will deal with at the beginning of the telecommunications industry. However, they later discovered that the human voice will produce 300 to 3300 cycle changes per second, or the electrical cycle of 3kHZ as the standard. As with any communication channel capacity, the telephone company does not want or need to provide users with too much, just enough to be able to carry voice conversations. Over the years, with the expansion of the network, telephone companies have limited the call bandwidth to 3kHz channel capacity. This is mainly based on cost considerations. Given the limited bandwidth, how can we talk through the network and generate a proper original language restoration signal? And how can it be cheaper? The generated frequency range is from 300 to 33001KHZ. The telephone company therefore restricts us to use the channel only within this range. When using radio frequency (RF) spectrum, the telephone company divides all capacity into 4kHz blocks. On each 41KHZ block (wire or radio channel), they install a frequency bandpass filter of 300 to 3300 volts. Any signal that falls within the RF spectrum allocation area can pass. Any signals outside the area will be filtered out. This is called a band limited channel. Because the voice can reach up to 51'riz, there are also cases where this frequency range (such as S and P sound words) is exceeded in the dialogue and is flattened by the filter. This may not sound reasonable, but it does make the line a little unclear. Neither human ears nor telephones have sufficient sensitivity, so there will not be too many problems. Once the electrical equivalent of the sound is produced (via a telephone or other device), electricity is sent to the line. When the call is on the line, the resistance of the line to the electrical signal will decrease its amplitude. The signal will become weaker and weaker. The loss of energy will eventually cause all the electrical energy to be absorbed, or make the signal unrecognizable. This is called "attenuation" of the electrical signal. Only a certain distance can be transmitted before the signal is consumed and disappears. It can be compared to the training of a relay athlete. The athlete tries his best to run around the 1/4 mile track. When the athlete reaches the end of the 1/4 mile, all the power and energy have been exhausted, and the athlete is exhausted. If no one catches the baton and he has to run around the track again, the second lap will never finish. In other words, the athlete will run around the track until he loses consciousness and falls to the ground. In order to keep the signal on the line, people use amplifiers to increase the signal strength. These amplifiers are usually spaced between 15,000 and 18,000 feet. Generally, only one amplifier (up to two) is required between the user's location and the call central office. The central office is usually close to the user's location, with an average of only 5-7 miles. Only in remote locations is it far from the central office. The second phenomenon that occurs on the line is with transmission. Noise (introduced by factors such as line loss, wire breakage, lightning, electrical induction, and heat) exists as white noise or intelligible sound. They start at the same time and cause the signal to deteriorate. Noise always exists on the trunk line, and cable faults will increase it, which in turn will cause the signal to deteriorate. Unfortunately, as the signal travels on the line, noise and multiples start to mix together. The amplifier cannot discern the noise from the actual dialogue. So not only does the amplifier enhance the signal, it also enhances the noise. This produces a stronger, but noisier signal. These signals in turn lead to extremely noisy circuits. The zoomed-in results accumulate with distance. The more amplifiers are used, the worse the resulting signal will be. Many long distance lines are continuously amplified. This does not mean that the telephone company does not want to do better, but is related to the combination of equipment, electrical performance and economy. Interestingly, if analog technology is still being widely used, some of the latest advancements in digital signal processing (DSP) can be used to clean up amplified speech transmission to some extent. But a better method for generating pure signals was developed many years ago. Cold Forging,Cold Forging Heatsink,Led Fin Heat Sink,Aluminum Led Heat Sink Dongguan Formal Precision Metal Parts Co,. Ltd , https://www.formalmetal.com
In the field of data and language communication, one of the most confusing areas is between the words "analog" and "digital". Most people know that "number" refers to information in the form of 1 and 0, but few people can make a psychological connection between this fact and the reality of moving voice signals in the format of 1 and 0. . Regarding the word "simulation", people may only talk about language communication. This will help you make and understand the connection between these two terms. After reading, you can know that you will not only become an electrical engineer, but also understand them well. If we have to understand something, it is: Analog and digital methods are methods of transmitting information in any medium. Some media are mainly suitable for analog, while others are suitable for digital, while others are both. This helps to understand the reasons for using different transmission systems. As mentioned earlier, the initial development of the "network" was just to provide voice communication services. The communication circuit that AT & T has established through Bell and its communication capabilities strictly uses analog technology. Indeed, it has become a digital world, but it is built around language and analog communication. What does all this mean?