Otaku Engineer in Great Tang Dynasty

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"Qing Que, have you tested this thing, how far can the maximum communication distance be?"

In the Qiqu Pavilion workshop, the scientific research base of the killer project, after trying this first-generation telephone several times, Li Zexuan called Li Tai over and asked indifferently.

He really did not expect the progress of the killer project to be so fast. At first, he thought that Datang would have to wait until next year at the earliest to build a "high-end product" like a telephone!

"Mr. Shan, Mr. Mo Chui and I have tested this before. When the distance is as far as one mile, the sound can't be heard clearly! At first we thought it was because of the loss of power during transmission, but we tried to increase the power supply voltage. , it will still be like this! Uh, there were two other test items that were burned out because of too much voltage~!"

At the end, Li Tai scratched his head, embarrassed.

Li Zexuan said speechlessly: "In this case, of course, you can't blindly increase the voltage. Some components in the telephone have a certain withstand voltage value. If you blindly boost the voltage without any basis, it will definitely cause the contents inside. irreversible damage!"

Li Tai said a little embarrassedly: "What the mountain chief taught! It's the blue bird Meng Lang~!"

He has not been in touch with electricity for a long time. It is very difficult to build a telephone according to the ideas and ideas provided by Li Zexuan. As for other details, how can he think so thoroughly~?

Li Zexuan shook his head and said, "Qing Que, it's your first time undertaking such a big project as the killer project. It's not easy to find a way to solve a problem. Engineering is a science that constantly explores the truth through experiments. Failure is not scary, what is scary is holding back because of the fear of failure!"

Having said this, Li Zexuan changed the subject and continued: "But I still hope that you can pay attention to safety during the experiment! Before you rashly increased the voltage, it was a small matter to burn things, causing the components to be broken down by high voltage and cause leakage. It's the big deal! Before you make a decision, you must think carefully and anticipate the consequences in advance!"

This is not Li Zexuan's alarmist. The first-generation telephone set by Li Tai is a simple circuit composed of some components connected by wires. It is very rough. Even Li Zexuan, the raw material for making circuit boards, is now difficult to get together!

In addition, there are many capacitors, diodes and transistors in the circuit of the telephone. Once something is broken down due to too high voltage, it is entirely possible that leakage will occur. At that time, the person holding the telephone is likely to be directly electrocuted. died!

Listening to Li Zexuan's solemn words, Li Tai's face also became serious. He solemnly cupped his hands and said, "Remember the teachings of the mountain chief!"

Li Zexuan nodded gratified. The little fat man in front of him was Li Er's baby. He could arrange for him to do scientific research by himself, but he must not let this little fat man finish his life, or Li Er would definitely not give him good fruits to eat. !

Therefore, the safety education for Li Tai must keep up!

"But Chief, why is the transmission distance of this phone only one mile~? This problem has troubled me and Mr. Mo Chui for a long time~!"

After a while, Li Tai returned to the topic and asked.

The major that Li Zexuan studied in his previous life can be called orthodox engineering, because it includes the most important branches of engineering, such as light, machinery, electricity, and arithmetic. Li Zexuan also knows a lot about communication. After a while, he slowly opened his mouth and said:

"Qing Que, although I have not disassembled your telephone, I also know that it can be roughly divided into two parts, the transmitter and the receiver, one is responsible for converting sound signals into electrical signals and transmitting them, the other is It is responsible for converting the received current signal into a sound signal, thus forming a complete loop that can transmit sound over long distances.

But this is only an ideal model. When it is actually used, it will encounter many problems, such as the short transmission distance you mentioned before, only one mile! That's because you didn't consider the loss of the signal and the noise in the line when you made the phone! "

Hearing this, Li Tai wondered: "Shan Chang, I know that this current will be lost in the process of transmission, but what do you mean by line noise?"

Li Zexuan thought for a while and replied, "In simple terms, in the circuit, noise is some electrical signal that we don't need, but it does exist! We just talked through the telephone, Qingque, you should be able to hear the inside of the telephone. In addition to my voice, there are some other "zizi" sounds, which are caused by electrical signal noise!

When the distance between the two ends of the telephone becomes longer, there will be more and more noise sources, and the useful signal will be lost. The sound is not surprising~! "

In fact, the first-generation telephone that Li Tai is making now is very similar to the first telephone made by Bell. It simply completed the mutual conversion of acoustic and electrical signals, but he did not consider the modulation and noise issues!

First of all, the frequency of the current signal output by the telephone is very low, and the recognition degree is also very low, and in the low frequency domain, there is a lot of noise, so in modern society, many people have added the output terminal of the telephone based on Bell's research. Modulator, by increasing the frequency, to increase the recognition of useful signals, and to facilitate long-distance transmission;

Of course, this modulator cannot adjust the frequency too high, because in wired transmission, high-frequency signals will have great transmission loss, and generally only in wireless transmission will the signal be modulated to a very high frequency;

Have

If there is a modulator, there must be a demodulator. In the improved telephones after Bell, a demodulator will be added to the front end to demodulate the signal. In addition, a filter system will be introduced to filter out the low-frequency stray noise… …

Regarding the detailed principles of the telephone, even if Li Zexuan told Li Tai for a whole day, he might not be able to finish it all, because when it comes to the concept of frequency domain, he has to mention two super geniuses - Euler and Fourier , It is too troublesome to talk about the "fame stunts" of these two people!

Even if Li Zexuan can explain it clearly, Li Tai may not be able to understand it. After all, concepts such as Euler's formula, Fourier transform, and Fourier series have stumped countless college students in modern society!

So Li Zexuan simply put forward two possible reasons. As for the truth behind this, let Li Tai slowly explore through practice and setbacks! You can't eat a big fat man in one bite, right?

Li Tai pinched his chin, stood there and thought for a long time, finally looked up at Li Zexuan and said, "Shan Chief, I roughly understand what you mean! But... But I still don't know how to reduce the signal. Transmission loss, and I don't know how to remove these noise sources you mentioned! Please ask the mountain chief to explain!"

Having said that, Li Tai bowed to Li Zexuan very sincerely.

For him, the "indigenous" of the Tang Dynasty, what Li Zexuan said before was too profound! But Li Tai likes challenges by nature. The more esoteric things he wants to understand, the more he wants to understand. Li Zexuan's words just now successfully aroused his thirst for knowledge! He wants to seek the truth!

"Cough! Qingque! This question is rather esoteric, and for you now, it is a bit beyond the outline. The engineering courses involved can only be learned in two or three years. Even if I tell you now, you can only learn it. I can hear a little bit of understanding!"

Li Zexuan shook his head and rationally chose to avoid the question. Li Tai opened his mouth reluctantly. Just as he was about to speak, Li Zexuan interrupted directly:

"Okay! Let's not discuss this problem, I will give you a feasible solution in a while, and now let's talk about the improvement of the telegraph!"

The main purpose of the second killer project of Yanhuang Academy is to improve the existing telegraph so that it can realize ultra-long-distance wireless communication. This work has actually been completed before Li Zexuan left Lantian County and went north to eliminate locusts. , the telegraph he brought to the north at that time was an improved one.

Hearing Li Zexuan say that a feasible solution will be given in a while, Li Tai just gave up and pondered for a while, then he said:

"Mr. Shan, the transformation of the telegraph body has basically entered the final stage. Now our telegraph transmitter has 15 or 6 times more power than before, and a detector has been added inside the telegraph. In this way, the telegraph The ability of the machine to identify electromagnetic waves is stronger than before! Next, the students plan to lead people to establish telegraph relay stations in Taiyuan and Yunzhou to conduct telegram reception and transmission relay experiments. Once these two relay stations are built, they can be directly in Changan Send a telegram to the steppe hinterland!"

Hearing this, Li Zexuan glanced at Li Tai with admiration, because the two telegraph relay stations chosen by Li Tai were very meaningful. In more than two months, Datang will send troops to the Turks. It was built before the war between the two countries, which is definitely an unparalleled good news for the Tang Dynasty, which means that the Tang army will be completely invincible in terms of message transmission!

This little fat man is worthy of being a royal son, he is definitely not something that ordinary people can have!

"Yeah! Qingque, you did a good job! The follow-up will follow your plan. Now is the summer vacation of the academy, just in time to concentrate all the elites of the academy to help you complete this work together! Try to complete the two telegrams within three months. Let's build a relay station!"

Patting Li Tai on the shoulder, Li Zexuan encouraged the latter.

"Don't worry, Tai Ding will go all out!"

Li Tai bowed his hands solemnly and responded.

After a while, Li Tai frowned again and said, "Lord Shan, Taiyuan and Yunzhou are far away from Lantian County, and there is no hydropower station there. It would be unrealistic to pass the line through, so how to solve the power supply problem of this telegraph relay station? "

Li Zexuan frowned, he really ignored this question!

The reason why a telegraph relay station is called a relay station is that its transmission power must be greater than the transmission power of the telegraph itself. It may not be long-term to rely on battery power alone, but as Li Tai said, there is no hydropower station in those two places. The river hydropower station is too far, and the power supply is indeed a big trouble!

After pondering for a long time, Li Zexuan said slowly: "Then build a small thermal power station locally!".

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