LOS Survey Training

7/27/2019 LOS Survey Training

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LOS survey training



Purpose for LOS survey

Methods of carrying out LOS survey

Contents



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Purpose of LOS survey

The purpose of the survey of microwave LOS transmission

is to collect information about the terrain and accurate

heights of structures, provide terrain profile diagrams, and

ensure that LOS transmission is available for the planningof microwave routes.




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Common survey methods are as follows:

1) Using the 1:50,000 (or a smaller scale) geographical map

2) Using the high-precision UTM or SRTM electronic map

3) Using the map downloaded from the Google Earth website

4) Direct-viewing method

5) Conventional measurement method

6) Electrical measurement method

Survey Methods for Microwave LOS

Transmission




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1:50,000 (or a smaller scale) geographical map


Transmission - Continued

Spacing between contour lines: 10 m

112 m




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Survey method by using the 1:50,000 (or a smaller scale) geographical map The most effective method for the survey of the long-distance microwave LOS transmission is to

obtain the sea-level elevations of the terrains that microwave rays pass on a 1:50,000 geographical

map and thus obtain a group of (distance (km) - sea-level elevation (m)) data.

Obtain the accurate geographical position of a site (latitude and longitude, or coordinates) after a site

survey. In addition, measure or estimate the heights of the structures at the blocking points.

Enter the obtained data of terrains and structures into the Pathloss software, and the Pathlosssoftware generates the corresponding microwave route profile diagrams.

The 1:50,000 geographical map has a high precision. Therefore, when you read the elevation data, the

height error can be controlled within 10 meters in most cases. This fully meets the requirement of

determining the height of a tower.






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Using the high-precision UTM or SRTM electronic mapCurrently, you can buy high-precision UTM or SRTM electronic maps in the market. After you

determine the latitude and longitude, you can use the Pathloss software to automatically read

the sea-level elevations of the terrains that microwave rays pass. Then, enter appropriate

structure heights according to the geographical environment in which the microwave project

is in, and the Pathloss software generates the corresponding microwave route profile diagrams.

Generally, this method is applicable only to the phase in which you pre-plan microwave routes(including the bidding phase). It is because the error of the available high-precision electronic

maps (90x90, 50x50, and 20x20) is still large. The elevation error may reach 50 to 60 meters.

If you determine the antenna height according to only these electronic maps in the

implementation phase, high risks may be caused.

You can directly use these electronic maps only in the case of wide open profiles.






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Using the map downloaded from the Google Earth websiteIn the case of important big cities in the world, you can download clear photos of the maps of

the cities from the Google Earth website without any charges. In addition, you can find the

required sites on the maps quickly by using the latitude and longitude. The maps show the

positions of streets, structures, and towers.

Mark the positions of the required microwave sites clearly on the maps and connect any two

sites by using straight lines. Hence, microwave route diagrams are formed and displayed on

the maps. You can find whether high-rise structures block microwave rays. In addition, you can

calculate the heights of microwave antennas by using terrain diagrams and the heights of

structures.

If required, use a distance meter to measure the heights of the high-rise structures on site.

If the project requires, pay to download more precise maps and the maps of wider areas from

the Google Earth website.






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Direct-viewing method

When the microwave transmission network exists in the downtowns where high-rise

structures crowd, 99% of the links are short or very short. If you can see the opposite site by

using your eyes and appropriate clearance exists, you can assume that the LOS transmission is

available.

In the case of downtowns, the terrain information with contour lines cannot be controlled (the

clearance condition is controlled by structures). Hence, you cannot find out whether the LOS

transmission is available by using terrain profiles.

You can use the following auxiliary methods and tools to check if the LOS transmission is

available:

A) High magnified telescope, digital camera

B) Red flag, balloon, reflector

C) Distance meter

D) Large-sized lifting crane (heavy and high cost, generally not used)






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Conventional measurement methodUse the land surveying method to measure microwave transmission profiles. The land

surveying method is the most original and precise, but costs the highest, and is the slowest.

Measure microwave transmission profiles one by one by using the geodetic points of the

country.

Generally, use the theodolite and the measuring scale to measure profiles.



Electrical measurement method

Test simulated microwave channels at the transmit point and the receive point by using

microwave test instruments. Compare the test data with the theoretical values obtained when

the microwave is transmitted in free space to check if the microwave channel is blocked and to

what degree the microwave channel is blocked.

The electrical measurement method requires the following instruments and meters: onestandard microwave signal generator, two broad-band bellmouth microwave antennas, one

low-noise amplifier, one microwave spectrum analyzer (or microwave signal receiver), and the

corresponding power supply devices



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