Practical procedure for calculating and constructing the VHF radio route
In this long and tedious article I will try to touch on the topic of calculating and building VHF radio routes from a practical point of view, based on my experience of similar work. This order does not pretend to be a priori correct and unique, for it is possible that someone has a completely different, more or less thorny one. Immediately make a reservation that all radio routes organized using protocols, classes and families such as GSM, WiFi, WiMax, LTE, BWA, RRL, etc., as mentioned in the first article, can be attributed to VHF radio channels.
So, we somehow had the need to organize a channel between two objects and there is a clear understanding that only the VHF radio route will save us. There are 3 different options for how this can be done.
1 option.
We rent the right channel from a carrier company that specializes in such activities. It’s not a fact that it will be a radio channel, for they proceed from their own considerations and resources. This is the easiest option, because it means that we only have to pay for installing and renting this channel. All other difficulties are solved by this carrier.
Option 2.
We order the desired radio channel from the contractor. Contractors, of course, are different. They can take on the full range of work on the organization of the radio channel, can take on only part of these works. Some, for example, are not ready to resolve issues with “supervisory and regulatory authorities”. Their services differ, of course, by price. This option differs from the first one in that the radio channel will belong to us, someone will not need to pay rent. And, of course, you will need to exploit this channel in the future.
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3 option.
We organize the radio channel yourself. We get the whole range of related difficulties, needs and problems. We can throw some of them on someone, we can do everything ourselves.
So, we decided to meet this need on our own. Where to begin?
1. To begin, no matter how strange and trite it sounds, we need to define these two points. You need to decide on either the exact address or specific coordinates on the map. Often it happens that only the name of the settlement in the immediate vicinity is known. Yandex maps , Google maps , here, of course, help out well. Although getting the coordinates in them is not so obvious if the address is not known. You can use something else, such as Google Earth . Or some other resources, such as OziExplorer . You can take the usual topographical paper map and navigate it.
The coordinates of the points can be determined by the navigator, arriving at the place.
2. If you have decided on the points, it is worth counting the radio path itself in order to determine the exact heights of the radio equipment suspension. The easiest way is to determine visually the presence of visibility. If it is, do not need to think about additional antenna-mast devices. You can see the route by hitting one of the points and determining the direction (azimuth) of the other. You can use binoculars or a telescope, you can take a couple of shots in the direction of another point with a camera with good sensitivity of the matrix, and then consider what happened. If visual visibility is limited by some obstacles, weather, or a distance of more than 2 km, the route must first be considered. This can be done or by any on-line calculator calculating VHF radio routes, at one time the radio equipment manufacturers gave such an opportunity on their websites, and some still provide for advertising purposes, for example , this one , or manually. For manual calculation, you can use the following method of calculating the radio path (see Figure 1):
a) Mark on the map the points of location of the transmitting (A) and receiving (B) antenna-feeder devices (AFU) and measure the distance:
b) Draw on the graph of the axis of rectangular coordinates:
abscissa axis - distance axis X,
y-axis - the axis of heights N.
c) Build a “zero level arc” - a sea level arc, having calculated the coordinates of intermediate points H = H (X) using the formula:
For a quick estimate of the maximum height of the “zero arc”, that is, in the middle of the radio path, you can use the formula:
For graphic construction of the “arc of the zero level”, it is enough to calculate 6-8 points.
d) Remove the elevation points along the radio path from the height map, plot their heights on the scale on the graph, counting from the “zero level arc” and connect the obtained points with a line, which will be the radio path profile.
e) We apply local barriers (buildings, woods, etc.) on the radio path profile line at a selected height scale, and the height of their antenna-feeder devices (equipment antenna height) at the VHF radio equipment deployment points. Next, connect the top points of the last straight line. This will be a “line of sight”.
e) Find the minimum distance h between the line of sight and the highest point of the radio path profile. Determine its coordinate - the distance X to this point.
g) Calculate the lumen value h1 (width of the first Fresnel zone), at which, at the point of reception B, the electromagnetic field strength is equal to the field strength of free space using the formula:
g) Compare the obtained values of the clearance h1 with the actual clearance on this route h. Based on the results of this comparison, a decision is made on the suitability of the route for organizing a radio link in the VHF band.
If the condition h> h1 is met - the track is open.
If h1> h, the route is half-closed and the radio path must have good energy.
If h <0 - the route is closed, you should start searching for the best route, or increase the height of the AFU suspension.
In conditions of low terrain, when the distance between the tracks is less than 25 km, you can restrict yourself to calculating the clearance h1 using the formula:
3. With the points of placement, the heights of placement of the equipment, the profile of the radio route were determined. Now it is necessary to decide on the equipment and frequencies. This is one of the main parts of the cost. We need to understand what channel capacity we need. I will not dwell on this, because when choosing it is necessary to proceed from the statements of the first article . In short, if you need high speeds and high packet performance, you will have to look towards the RRL. If the speed is less than 500 Mbit / s, then it is worth looking in the direction of either a 70-86 GHz bandwidth solution, or broadband wireless access (BWA, 5-7 GHz band).
4. With the equipment, frequencies and everything else that preceded it, decided. It would seem that everything, nothing more is needed. But no. It is necessary. And most often, what was done earlier seems to be small flowers. Now begins the most important thing - the design of the desired radio frequencies. This is generally a separate topic. For a start, it is worth ordering a study of the desired radio path in the HRCHC in order to check its calculations, for the money is not big. But if you are confident in the correctness of their calculations, you should immediately begin the procedure of registration of these frequencies. I will not discuss this topic in detail, because it directly depends on the “information exchange” with the HRPC , the Ministry of Defense, RosKomNadzor and other regulatory bodies. In short, the HRDC is looking at the electromagnetic compatibility (EMC) of our equipment in a specific place and at a specific frequency, coordinates the frequency with the Ministry of Defense. If the EMC is OK, the frequency is not busy, the military gave a go-ahead for its use, then we get a positive decision on the frequency. Then pay the bribe and get permission in RosKomNadzor. If someone gave a “hang up” - we return to p. 3. Costs for this item are another major part of the costs. I will add that often, getting into this process, many people give up on the idea of organizing a radio channel on their own.
Sometimes, amalicious violator who realistically assesses risks, skips a given item. What in this case threatens? If we are caught in the “illegal” use of the state’s resources, i.e., frequencies, they will be fined (not very much the first time) and given an order to eliminate the shortcomings. If we ignore, then the instruction will be given again. For the third time, they will take the license away from the operator and dismantle the iron. And when can they "catch us by the hand"? If someone complains or we get under a scheduled check of the electromagnetic resistivity of the HRSTs. Usually, competitors who have crossed the road usually complain, or a grandmother, who has “a headache due to radiation”. How often does it happen or will it be at all? What will we lose if we get? Commercial risks, however.
Probably this is why mobile operators, including those from the Big Three, are considered to be “malicious” violators in the HRCH. After all, the larger the network, the greater the risks and the lower the initial profitability.
5. Well, finally, there is permission and the desire to build is not lost. Now it's up to the project and its approval by the regulator.
Often this point and the next one are combined in time with point 4. However, then there is a risk of being mistaken with frequencies.
Often the project is not done and not agreed, it all depends on the capacity of the radio channel, its type and the communication protocol used.
6. Well, we finally arrived at the construction site. They were built, everyone is happy and "throw their caps into the air." Now you need to inform the regulator of the type of equipment, its mac-address, operating frequency, suspension height, power. In response, you will receive a notification about the registration of the track. If they are not built, then the frequency resolution can be lost after some time. Now our radio route will be periodically checked in the HRCHC for compliance with the issued permits. Therefore, if someone by mistake when setting up the radio equipment forgot to turn off the “adaptive frequency tuning for interference,” wait for the prescription and the penalty. If you change the mac-address by accident, for example, then in theory you also need to inform the regulator.
To the uninitiated, this order may seem too cumbersome. So it is in my opinion. But if you think about it, then about all the activities of the Russian telecom.
So, we somehow had the need to organize a channel between two objects and there is a clear understanding that only the VHF radio route will save us. There are 3 different options for how this can be done.
1 option.
We rent the right channel from a carrier company that specializes in such activities. It’s not a fact that it will be a radio channel, for they proceed from their own considerations and resources. This is the easiest option, because it means that we only have to pay for installing and renting this channel. All other difficulties are solved by this carrier.
Option 2.
We order the desired radio channel from the contractor. Contractors, of course, are different. They can take on the full range of work on the organization of the radio channel, can take on only part of these works. Some, for example, are not ready to resolve issues with “supervisory and regulatory authorities”. Their services differ, of course, by price. This option differs from the first one in that the radio channel will belong to us, someone will not need to pay rent. And, of course, you will need to exploit this channel in the future.
')
3 option.
We organize the radio channel yourself. We get the whole range of related difficulties, needs and problems. We can throw some of them on someone, we can do everything ourselves.
So, we decided to meet this need on our own. Where to begin?
1. To begin, no matter how strange and trite it sounds, we need to define these two points. You need to decide on either the exact address or specific coordinates on the map. Often it happens that only the name of the settlement in the immediate vicinity is known. Yandex maps , Google maps , here, of course, help out well. Although getting the coordinates in them is not so obvious if the address is not known. You can use something else, such as Google Earth . Or some other resources, such as OziExplorer . You can take the usual topographical paper map and navigate it.
Once upon a time, I was somewhat discouraged when I discovered on the Mitinsky market scans of topographic maps of the General Staff of the Armed Forces of the Russian Federation 1: 100,000 (1 cm - 1 km) with a shaded "secret" sign.
The coordinates of the points can be determined by the navigator, arriving at the place.
Somehow, about 5 years ago, we worked together with the guys from the HRCHC . I noticed that they write coordinates in the reports without seconds. A clear answer was given to my question: “We still have laws in our country, according to which, if you can determine your location with an accuracy greater than 30 meters, you will be prosecuted.”
2. If you have decided on the points, it is worth counting the radio path itself in order to determine the exact heights of the radio equipment suspension. The easiest way is to determine visually the presence of visibility. If it is, do not need to think about additional antenna-mast devices. You can see the route by hitting one of the points and determining the direction (azimuth) of the other. You can use binoculars or a telescope, you can take a couple of shots in the direction of another point with a camera with good sensitivity of the matrix, and then consider what happened. If visual visibility is limited by some obstacles, weather, or a distance of more than 2 km, the route must first be considered. This can be done or by any on-line calculator calculating VHF radio routes, at one time the radio equipment manufacturers gave such an opportunity on their websites, and some still provide for advertising purposes, for example , this one , or manually. For manual calculation, you can use the following method of calculating the radio path (see Figure 1):
a) Mark on the map the points of location of the transmitting (A) and receiving (B) antenna-feeder devices (AFU) and measure the distance:
AB = D
b) Draw on the graph of the axis of rectangular coordinates:
abscissa axis - distance axis X,
y-axis - the axis of heights N.
c) Build a “zero level arc” - a sea level arc, having calculated the coordinates of intermediate points H = H (X) using the formula:
H (X) = (D² / 2R) * K * (1-K), km, where
D is the length of the VHF radio link, km;
R is the radius of the Earth - 6371 km;
K = X / D is the relative coordinate of the intermediate point, 0 <K <1;
X - distance to intermediate point, km.
For a quick estimate of the maximum height of the “zero arc”, that is, in the middle of the radio path, you can use the formula:
Hmax = D² / 51
For graphic construction of the “arc of the zero level”, it is enough to calculate 6-8 points.
d) Remove the elevation points along the radio path from the height map, plot their heights on the scale on the graph, counting from the “zero level arc” and connect the obtained points with a line, which will be the radio path profile.
e) We apply local barriers (buildings, woods, etc.) on the radio path profile line at a selected height scale, and the height of their antenna-feeder devices (equipment antenna height) at the VHF radio equipment deployment points. Next, connect the top points of the last straight line. This will be a “line of sight”.
e) Find the minimum distance h between the line of sight and the highest point of the radio path profile. Determine its coordinate - the distance X to this point.
g) Calculate the lumen value h1 (width of the first Fresnel zone), at which, at the point of reception B, the electromagnetic field strength is equal to the field strength of free space using the formula:
h1 = ² √ [1/3 * D * λ * K * (1 - K)], where
h1 - the value of the "lumen",
D is the length of the radio path in m,
λ is the length of the working radio wave in m,
K = X / D is the relative coordinate of the intermediate point, 0 <K <1;
X - the distance to the point of obstacles, in m.
g) Compare the obtained values of the clearance h1 with the actual clearance on this route h. Based on the results of this comparison, a decision is made on the suitability of the route for organizing a radio link in the VHF band.
If the condition h> h1 is met - the track is open.
If h1> h, the route is half-closed and the radio path must have good energy.
If h <0 - the route is closed, you should start searching for the best route, or increase the height of the AFU suspension.
In conditions of low terrain, when the distance between the tracks is less than 25 km, you can restrict yourself to calculating the clearance h1 using the formula:
h1 = {[(Ha + Hb) + (ha + hb)] / 2} - (hprep + Hmax), where
Ha, Nb - the height of the terrain at the points of installation of both AFU, determined by the map, m;
ha, hb are the heights of the AFUs themselves (the height of the equipment suspension), m;
hprep - the greatest height of the obstacles on the radio path, m;
Hmax - maximum height of the “arc of the zero level” in the middle of the radio path, m.
3. With the points of placement, the heights of placement of the equipment, the profile of the radio route were determined. Now it is necessary to decide on the equipment and frequencies. This is one of the main parts of the cost. We need to understand what channel capacity we need. I will not dwell on this, because when choosing it is necessary to proceed from the statements of the first article . In short, if you need high speeds and high packet performance, you will have to look towards the RRL. If the speed is less than 500 Mbit / s, then it is worth looking in the direction of either a 70-86 GHz bandwidth solution, or broadband wireless access (BWA, 5-7 GHz band).
4. With the equipment, frequencies and everything else that preceded it, decided. It would seem that everything, nothing more is needed. But no. It is necessary. And most often, what was done earlier seems to be small flowers. Now begins the most important thing - the design of the desired radio frequencies. This is generally a separate topic. For a start, it is worth ordering a study of the desired radio path in the HRCHC in order to check its calculations, for the money is not big. But if you are confident in the correctness of their calculations, you should immediately begin the procedure of registration of these frequencies. I will not discuss this topic in detail, because it directly depends on the “information exchange” with the HRPC , the Ministry of Defense, RosKomNadzor and other regulatory bodies. In short, the HRDC is looking at the electromagnetic compatibility (EMC) of our equipment in a specific place and at a specific frequency, coordinates the frequency with the Ministry of Defense. If the EMC is OK, the frequency is not busy, the military gave a go-ahead for its use, then we get a positive decision on the frequency. Then pay the bribe and get permission in RosKomNadzor. If someone gave a “hang up” - we return to p. 3. Costs for this item are another major part of the costs. I will add that often, getting into this process, many people give up on the idea of organizing a radio channel on their own.
Sometimes, a
Probably this is why mobile operators, including those from the Big Three, are considered to be “malicious” violators in the HRCH. After all, the larger the network, the greater the risks and the lower the initial profitability.
5. Well, finally, there is permission and the desire to build is not lost. Now it's up to the project and its approval by the regulator.
Often this point and the next one are combined in time with point 4. However, then there is a risk of being mistaken with frequencies.
Often the project is not done and not agreed, it all depends on the capacity of the radio channel, its type and the communication protocol used.
6. Well, we finally arrived at the construction site. They were built, everyone is happy and "throw their caps into the air." Now you need to inform the regulator of the type of equipment, its mac-address, operating frequency, suspension height, power. In response, you will receive a notification about the registration of the track. If they are not built, then the frequency resolution can be lost after some time. Now our radio route will be periodically checked in the HRCHC for compliance with the issued permits. Therefore, if someone by mistake when setting up the radio equipment forgot to turn off the “adaptive frequency tuning for interference,” wait for the prescription and the penalty. If you change the mac-address by accident, for example, then in theory you also need to inform the regulator.
To the uninitiated, this order may seem too cumbersome. So it is in my opinion. But if you think about it, then about all the activities of the Russian telecom.
Source: https://habr.com/ru/post/257731/
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