Chapter 747 It will be much easier to solve the problem if we separate them

"Chief Engineer Gao, you don't have to save face for us. Just tell us if you have any questions. We are here to learn." Chief Lin wiped the face off his face and put it in his pocket. Work was more important.

Gao Zhendong was more than happy to do so. He had initially planned to skip it, mainly out of consideration for his comrades' feelings. Since he didn't care, that was the best.

He explained the frequency band planning issues to General Manager Lin and others in detail.

For example, the positioning accuracy is slightly poor due to the frequency being too low, the receiving and transmitting at the same frequency may cause spontaneous oscillation and burn out the machine, and the lack of channel division may lead to congestion of device requests, etc.

After hearing this, Mr. Lin and the others broke out in cold sweats. This thing looks simple, but they didn't expect it to have so many problems?

This situation is very common in our early scientific research, that is, the principle is fine, the implementation has been achieved, but the details are not very reliable. Because of lack of experience, the details accumulate and become a big problem. The final result is that after a lot of tinkering, we come up with something that seems to be usable, but is not very usable.

"Chief Engineer Gao, do you have any suggestions on this channel division?" Since Chief Engineer Gao found the problem at a glance, there must be a solution. At least there is a directional solution, which can save a lot of time in exploration.

Gao Zhendong smiled and said, "Actually, I don't need to come up with this plan. Someone has already come up with it."

"Ah? Is there anyone in the country who is so advanced?"

"Not in China. In recent years, a new set of civil navigation equipment and regulations have been put into use internationally. Its frequency band selection, channel division, response process, and carrier information are all public. Just use that."

Considering that the TACAN tactical navigation system was put into use in 1955, and the frequency band division of the civil navigation and ranging system DME was completed in 59 and put into use in 61, and the frequency band divisions of the two are exactly the same, DME can also inquire and respond to TACAN's navigation stations and navigation terminals.

The biggest difference is TACAN's angle measurement signal, which cannot be obtained by DME. Civil aviation angle measurement uses VOR, and the principle is the same as TACAN, but VOR and DME have different frequency bands, while TACAN's angle measurement and distance measurement are completed within the same frequency band.

Therefore, Gao Zhendong believes that DME is actually the civilian application of TACAN technology, which is a very common thing during the Cold War. Military use comes first, and civilian use comes later.

"Civilian use? Isn't it inappropriate to mix it with civilian use?" asked General Manager Lin.

"We are sharing the same airspace, so military-civilian compatibility is essential. It's just that we need to separate the military and civilians in the design. This is also done in other countries. We can learn from their experience in this regard. This frequency band can achieve a positioning accuracy of 370 meters and a maximum range of about 550 kilometers, which is basically enough for the Air Force and Navy."

Although its accuracy and range cannot be compared with those of several major global satellite positioning systems in the future, it is more than sufficient for the navy and air force.

Again, in this regard, Citibank is trustworthy! Why bother thinking about it?

"Well, Mr. Gao, what you said makes sense. We will go find the foreign affairs department and the civil aviation comrades to get a set of relevant information. This kind of civil aviation industry public information should not be a big problem." Mr. Lin and his colleagues had nothing to do with civil aviation and did not know there was such a thing. But now that they know about it, it is much easier to deal with. The civil aviation comrades should have channels, even if it is something led by the Oceania Treaty Organization.

In this regard, Gao Zhendong had no idea of ​​making a set of his own. It would be fine as long as he could get it. There was no need to show it off in front of others. The chance to win a lottery was very valuable now.

"Well, the problem of distance measurement is that as long as you do this well and combine it with the triangulation positioning technology you already have, it won't be a big problem. The remaining problem is angle measurement."

Hey, after Chief Engineer Gao disassembled this matter like this, it seems that it is not that difficult anymore. At least half of it has been solved. It is the remaining half that is the most troublesome.

It can be said that single-station distance measurement does not pose any essential difficulties for our current technology, but single-station angle measurement is a very troublesome matter. Let's not talk about anything else, just look at when we got a truly reliable tactical navigation system, which was in the 80s.

"Mr. Gao, to be honest, we have no idea how to measure the angle. We have been thinking about it for a long time, but we still can't come up with a solution for measuring the angle with a single base station."

Gao Zhendong smiled and said, "In fact, the principle is not difficult. The simplest way is to use a 360-degree radar to do this."

"360 degrees is easy, but there is still no way to tell the angle. We have considered using a narrow-lobe radar that can rotate and scan 360 degrees. When the positioning terminal knows which direction the radar will scan at which time, it can calculate its own angle by combining the radar signal peak with the signal reception time."

Mr. Lin and his colleagues were not just thinking about waiting, relying on, and asking for things. They still thought of many ways, but the results were not satisfactory.

"But in the end, there is no problem in principle, but there are big problems in implementation. The clock accuracy requirements are too high. The introduction of clock synchronization, not to mention that the clock synchronization itself has a synchronization time problem, even if it is synchronized, it will quickly fall to the point where it cannot be used. The radar lobe performance requirements are also very high, and the angle measurement error is large. It is technically difficult to achieve a usable level."

Gao Zhendong was delighted. This was the simplest principle, but it required the most complex and advanced technology. Many technologies are like this. If the principle looks simple, but no one has technically implemented it to a certain extent, it often means one thing - it is extremely costly to make this principle usable.

He stood up and picked up the chalk.

"The 360-degree radar signal I mentioned is not only about achieving omnidirectional coverage, but also contains other information in this 360-degree radar signal. You can see it here."

After saying that, he started drawing on the blackboard.

"The amplitude and phase of the radar signal are modulated in 360 degrees. In theory, in each direction, both are different from those in other directions. In this way, the envelope of the radar signal can indicate the location of the receiving terminal."

Mr. Lin thought Gao Zhendong’s idea was really brilliant.

Modulating phase and amplitude is not a big problem for current technology. It immediately reduces a level in terms of principle and implementation difficulty.

"Then how do we know how much the phase of the signal has changed? If we don't know the degree of change, then even if we receive the signal, we won't be able to determine our angle relative to the base station." asked a comrade who is in charge of positioning.

Gao Zhendong smiled and said, "This is simple. While transmitting the modulated signal, we also need to omnidirectionally transmit a reference signal with a constant phase. After these two signals have been processed by limiting and frequency discrimination, they are sent to the phase comparator. Once compared, the result will come out, hahaha."

"Chief Engineer Gao, why not just modulate the amplitude or frequency? In communications, amplitude modulation and frequency modulation are also common means of carrying information."

Gao Zhendong said: "The amplitude must be combined with the phase, because the position of the positioning terminal from the base station is uncertain, and the amplitude will attenuate. It is difficult to locate the direction based on the amplitude alone. The frequency is even more troublesome. If continuous frequency modulation is used, the frequency band is narrow and the resolution is insufficient. The frequency band is wide, and large-bandwidth equipment is difficult to use. And there is another problem. If there is relative motion between the two, there will be a Doppler effect, which will cause frequency shift. This frequency shift is more troublesome than the phase shift caused by the Doppler effect."

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Mr. Lin is fine. He can think of answers to some questions, such as the problem with the phase comparator.

But other comrades were all impressed by Gao Zhendong's careful thinking. He was able to sit in the position of chief engineer at such a young age. He was indeed not an ordinary person. The only problem was that he was the chief engineer of a steel plant, which always made them feel weird.

Mr. Lin looked at the schematic diagram drawn by Gao Zhendong and thought about it again and again. The more he thought about it, the more he felt that this method was feasible.

This is definitely feasible, the Citigroup guy has been there before.

"What is the angle measurement accuracy of this device?"

Gao Zhendong thought for a moment and said: "With current technical conditions, we can probably achieve an angle measurement accuracy of 2 to 3 degrees."

The angular measurement accuracy of TACAN is about 1.4 to 2 degrees. Although it may not seem high, it is much more accurate than a compass. Moreover, for the navy and air force, this accuracy is really sufficient. If converted to 360 degrees, the error of 3 degrees is about 8 thousandths, less than %.

For today's navy and air force, let alone 3 degrees, even 5 to 6 degrees will make them fly with joy as long as they are reliable at work.

In fact, the error of triangulation positioning is not necessarily smaller than this.

General Lin was overjoyed: "Well, this is enough to meet the requirements of the Navy and Air Force! In this way, the main contradiction is concentrated on the phase comparator. This is much easier to deal with, hahahaha."

If before coming here he just wanted to get some help and see if he could find a direction, then now he can be said to be full of confidence.

Chief Engineer Gao broke down a big problem into three small problems: distance measurement, angle measurement, and communication. Then he thoroughly solved the two small problems of distance measurement and communication with ease, and finally solved most of the small problem of angle measurement.

If I still can't develop a usable single-base station positioning tactical navigation system at this point, then I'd better pull out my horse's tail and hang myself at the door of the Defense Work Committee.

"Chief Engineer Gao, thank you so much! You have solved our big problem!" General Manager Lin stood up and shook Gao Zhendong's hand. He knew that this sentence was very pale, but as a traditional technician, he seemed unable to say anything more appropriate and fancy. He could only shake Gao Zhendong's hand vigorously to show that his words were very sincere.

Gao Zhendong was still modest: "This system is not without flaws."

(End of this chapter)