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Path Profiling Reaction Paper

Dianne Claudinne E. Mapanoo

Mapua Institute of Technology This contains the summary of what was presented by the reporter and comments about how the report was presented. This also

contains some recommendations on how the report can be improved. This paper also contains the research and additional information about the topic presented.

I. REACTION HE REPORT which was discussed last Wednesday, January 22, is about path profiling. A group discussed the topic

with four members. They discussed the definition and principles regarding path profiling. The group used a powerpoint presentation to discussed the topic and the sample computations. As for discussing the radio mobile, the group showed a video to show a tutorial on how to use the radio mobile. The group showed steps on how to path profiling is done but does not showed any examples to show each step. It is recommended that the reporters show examples regarding on manual path profiling.

II. RESEARCH

A. Line of Sight Propagation

Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line. The rays or waves may be diffracted, refracted, reflected, or absorbed by atmosphere and obstructions with material and generally cannot travel over the horizon or behind obstacles.

At low frequencies (below approximately 2 MHz or so)

radio signals travel as ground waves, which follow the Earth's curvature due to diffraction with the layers of atmosphere. This enables AM radio signals in low-noise environments to be received well after the transmitting antenna has dropped below the horizon. Additionally, frequencies between approximately 1 and 30 MHz can be reflected by the F1/F2 Layer, thus giving radio transmissions in this range a potentially global reach, again along multiple deflected straight lines. The effects of multiple diffraction or reflection lead to macroscopically "quasi-curved paths".

However, at higher frequencies and in lower levels of the

atmosphere, neither of these effects is significant. Thus any obstruction between the transmitting antenna and the receiving antenna will block the signal, just like the light that the eye may sense. Therefore, since the ability to visually see a transmitting antenna (disregarding the limitations of the eye's resolution) roughly corresponds to the ability to receive a radio signal from it, the propagation characteristic of high-frequency radio is called "line-of-sight". The farthest possible point of propagation is referred to as the "radio horizon".

In practice, the propagation characteristics of these radio waves vary substantially depending on the exact frequency and the strength of the transmitted signal (a function of both the transmitter and the antenna characteristics). Broadcast FM radio, at comparatively low frequencies of around 100 MHz, are less affected by the presence of buildings and forests.

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B. Earth Bulge Earth bulge is a term used in telecommunications. It refers

to the circular segment of earth profile, which blocks off long distance communications.

• DISTANCE TO HORIZON

Assuming a perfect sphere with no terrain irregularity, the distance to horizon from a high altitude transmitter (i.e. line of sight) can readily be calculated.

Let R be the radius of Earth and h be the altitude of a telecommunication station. Line of sight distance d of this station is given by the Pythagorean theorem;

Since the altitude of the station is much less than the radius of the Earth,

The mean radius of the earth is about 6,378 kilometres (3,963 mi). (See Earth radius) Using the same units for both the altitude of the station and the radius of the earth,

If the height is given in m. and distance in km.

If the height is given in ft. and the distance in miles,

C. Path Profile At UHF and microwave frequencies, when you deploy an

RF link between two distant sites you need to make sure you have "line of sight" between the two antennas. But at these frequencies "line of sight" does not simply mean that from one site you can "see" the other. When your distance exceeds, say, 5 miles (8 Km), you need to take into account the following

factors:

! The curvature of the earth. ! Fresnel Zone clearance. ! Atmospheric refraction.

The figure below illustrates these concepts with an exaggerated representation of a long link. The following sections describe these effects.

D. Radio Mobile

Radio Link parameters between selected Units can be examined using the Radio Link pane, with an elevation grid displayed if required. This grid shows the height matrix round the cursor cross wires and can also include a magnified view of the cursor location if required.

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Individual Radio Link performances between pairs of Units can be selected and displayed by the program, with the ground profile and other Link parameters being displayed. Land Coverage data can also be downloaded and then included in the propagation path calculations.