Chapter 747 It will be much easier to solve the problem if it is broken down
"General Engineer Gao, you don't have to save face for us. If you have any questions, just ask us. We are here to learn." Mr. Lin wiped the shame off his face and put it in his pocket. Work is important.
Gao Zhendong didn't want it. He was ready to skip it at first, mainly because he considered the feelings of his comrades. Since he didn't care, that was the best.
He explained the frequency band planning issue to Mr. Lin and others in detail.
For example, if the frequency is too low, the positioning accuracy will be slightly poor. Transmitting and receiving on the same frequency may cause spontaneous oscillation and burn out the machine. Failure to divide channels may lead to congestion of device requests, etc.
Mr. Lin and the others were all covered in cold sweat. This thing looked 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 OK and the implementation is achieved, but the details are not reliable. Because there is no experience, the details accumulate too much, and it becomes a big problem. The problem is that the final result is to fiddle around and get something that seems to work, but is not very useful.
"Chief Engineer Gao, do you have any suggestions for this channel division?" Since Chief Engineer Gao found the problem at a glance, he presumably has a solution, at least directional, which can save a lot of time.
Gao Zhendong smiled and said: "In fact, I don't need to come up with this plan. Someone has already come up with it."
"Huh? Is there anyone in China who is so advanced?"
"Not domestically. 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 one."
Considering that the TACAN tactical navigation system was put into use in 1955, and the civilian navigation ranging system DME frequency band allocation was completed in 1959 and put into use in 1961, and the two frequency band allocations are completely consistent, DME can also inquire and reply to TACAN’s navigation station and Navigation terminal.
The biggest difference is that TACAN's angle measurement signal is not available to DME. Civil aviation angle measurement uses VOR. The principle is the same as TACAN's, but the VOR and DME frequency bands are different, and TACAN's angle measurement and ranging are in the same signal. Completed within the frequency band.
Therefore, Gao Zhendong believes that DME is actually the decentralization of TACAN technology for civilian use. This was a very common thing during the Cold War. Military use comes first, and civilian use comes later.
"Civil use? Isn't it inappropriate to mix it with civilian use?" Mr. Lin asked.
"Originally we share the same airspace, and military-civilian compatibility is necessary. However, in terms of design, military-civilian isolation is sufficient. This is also done abroad. In this regard, it is still possible to learn from their experience. This frequency band can achieve 370 The positioning accuracy of meters and the maximum ranging range of about 550 kilometers are basically sufficient for the Air Force and Navy. ”
Regardless of the accuracy and range, it is not comparable to the major global satellite positioning systems in the future, but it is very useful for the navy and air force.
Again, in this regard, Citi Selection is trustworthy! Stop thinking about it.
"Well, Mr. Gao, what you said makes sense. Let's go back and find comrades from the foreign affairs department and civil aviation to find a set of relevant information. This kind of information disclosed by the civil aviation industry is not a big problem." Mr. Lin and the others have nothing to do with civil aviation. I didn't know that there was such a thing, but now that I know it, it's much easier to handle. Comrades in civil aviation probably have channels, even if it is something led by the Ocean Convention Organization, it is no exception.
In this regard, Gao Zhendong has no idea of making a set by himself. As long as he can get it, he does not have to show it to others. The lottery opportunities are very valuable now.
"Well, as for the problem of distance measurement, as long as you do this well and combine it with your original triangulation positioning technology, it won't be a big problem. The remaining problem is angle measurement."
Hey, after Chief Engineer Gao has taken this matter apart, it seems that it is really not that difficult. 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 ranging does not have any inherent difficulties with our current technology, but single-station angle measurement is a big problem. If nothing else, let’s talk about when we got it Just look at the truly reliable tactical navigation system from the 1980s.
"Mr. Gao, to tell you the truth, we have no clue about angle measurement right now. We have been thinking about angle measurement with a single base station for a long time, but we still can't figure out a way."
Gao Zhendong smiled and said: "Actually, the principle is not troublesome. The simplest way is to use a 360-degree radar to do this."
"360 degrees is easy to handle, but there is still no way to distinguish the angle. We have considered using a narrow-beam radar with 360-degree rotation and scanning. When the positioning terminal knows which direction the radar will scan at which time, it can use the radar signal peak value Calculate your own angle based on the signal reception time.”
Mr. Lin and the others were not just thinking about waiting, relying, and wanting. They still thought of many ways, but the results were not satisfactory.
"But in the end, there is no problem in principle, but there is a big problem in implementation. The accuracy requirements of the clock are too high, and clock synchronization is introduced. Not to mention that clock synchronization itself has a synchronization time problem. Even if it is synchronized, it will be very fast. If it falls to the point where it cannot be used, the radar lobe performance requirements are also very high, and the angle measurement error is very large, so it is technically difficult to reach a usable level. ”
Gao Zhendong was amused. This was the simplest principle, but it required the most complex and advanced technology. Many technologies are like this. If the principle seems very simple, but no one has technically implemented this principle to a certain extent, it often means one thing - it is extremely expensive for this principle to reach a usable level.
He stood up and picked up the chalk.
"The 360-degree radar signal I am talking about not only achieves omnidirectional coverage, but also contains other information in this 360-degree radar signal. Look here."
After speaking, he started drawing a picture on the blackboard.
"In the 360-degree direction, the amplitude and phase of the radar signal are modulated. Theoretically, in each direction, both are different from other directions. In this way, through the envelope of the radar signal, we can Indicates the location of the receiving terminal.”
Mr. Lin thought Gao Zhendong's idea was so brilliant.
Modulation phase and amplitude are not a big problem for current technology. The principle and implementation difficulty have suddenly dropped to a level.
"Then how do you know how much the phase of the signal has changed? If you don't know the degree of change, then even if you receive the signal, you can't determine your angle relative to the base station." asked a comrade who was doing positioning.
Gao Zhendong smiled: "This is simple. While transmitting the modulated signal, it also transmits a reference signal with the same phase in all directions. After the two signals undergo necessary processing such as amplitude limiting and frequency discrimination, they are sent into the phase Comparator, once compared, the result will come out, hahaha.”
"General 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 inherently attenuate. It is difficult to locate the direction by amplitude alone. Frequency is even more troublesome. If it is continuously modulated, The frequency band is narrow and the resolution is not enough , the frequency is wide, and it is difficult to install large-bandwidth equipment. Another problem is that there is relative motion between the two, and there is a frequency shift compared to Doppler. The phase shift caused by the effect is even more troublesome.”
Fortunately, Mr. Lin can think of answers to some questions, such as the phase comparator problem.
But other comrades all admired Gao Zhendong's thoughtfulness. He was definitely not an ordinary person to sit in the position of chief engineer at such a young age. The only problem was that he was the chief engineer of a steel plant, which they always found strange. of.
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 must be possible, Citigroup has done it before.
"How accurate can this angle measurement be?"
Gao Zhendong thought for a while: "With the current technical conditions, we can probably achieve an angle measurement accuracy of 2 to 3 degrees."
The angle measurement accuracy of TACAN is about 1.4 to 2 degrees. Even though it doesn’t look high, it is much more accurate than a compass, and for the navy and air force, this accuracy is really sufficient. When converted to For 360 degrees, the error of 3 degrees is about 8 thousandths, which is less than 1 percent.
For the current navy and air force, let alone 3 degrees, it is 5 to 6 degrees. As long as it works reliably, they can fly happily.
The error of triangulation positioning is actually not necessarily smaller than this.
Mr. Lin was overjoyed: "Well, this is enough to meet the requirements of the navy and air force! In this way, the main contradiction will focus on the phase comparator, which will be much easier to handle, hahaha."
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.
A big problem was broken down into three small problems by Chief Engineer Gao: ranging, angle measurement, and communication. Then he completely solved the two small problems of ranging and communication with ease, and finally solved more than half of the small problem of angle measurement. .
If you still can't come up with a usable single-base station positioning and tactical navigation system at this point, then you can hang yourself by the tail of the horse at the door of the National Defense Work Committee.
"General Manager Gao, thank you so much! You solved our big problem!" Mr. Lin stood up and held Gao Zhendong's hand. He knew that this sentence was very pale, but as a traditional technician, he seemed to be unable to say it. I couldn't think of anything more suitable and fancy, so I could only shake Gao Zhendong's hand vigorously to show that I really meant what I said.
Gao Zhendong is still modest: "This system is not without its faults."
(End of chapter)