radio engineering - line of sight

7/25/2019 Radio Engineering - Line of Sight

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Rekayasa RadioTTG4B3SEMESTER GANJIL 2015 2016


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LINE OF SIGHT CONCEPTS

Line-of-Sight

Microwave radio communication requires a clear line -of-sight (LOS) conditionUnder normal atmospheric conditions, the radio horizonis around 30 percent beyond the optical horizon

Radio LOS takes into account the concept of Fresnelellipsoids and their clearance criteria


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How to improve LOS?

Raise the antenna mounting point on the existing structureBuild a new radio tower, which is tall enough to mount theantennaIncrease the height of an existing towerLocate a different mounting point, i.e. building or tower, forthe antenna


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The Concept of Line-of-Sight (LOS)

No obstructions between each endo No treeso No buildingso No mountainso Note: The lower the frequency, the better it will travel

through obstacles


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The Line-of-Sight Issue -raising one side

A structure can be erected to establish line -of-sight overobstacles


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The Line-of-Sight Issue -raising two side

Two structures can be erected to establish line -of-sight overobstacles


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The Line-of-Sight Issue using a repeater

A system approach called a repeater can establish line -of-sight to go around or over obstacles

Active repeaters (two radio systems back-to-back) Passive repeaters (one radio system redirected)


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The Line-of-Sight Issue using a repeater

Active repeaters (two radio systemsback-to-back)


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The Line-of-Sight Issue using arepeater

Passive repeaters (one radio systemredirected)


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Line-of-Sight Considerations

The Fresnel zone is additional path clearance that is required tooptimize radio receptionThere are an infinite number of points where reflected signal arrivesexactly wavelength out of phase for a given frequency


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Typically the first Fresnel zone (N=1) is used to determine obstruction lossThe direct path between the transmitter and the receiver needs aclearance above ground of at least 60% of the radius of the first Fresnelzone to achieve free space propagation conditionsEarth -radius factor k compensates the refraction in the atmosphere

Clearance is described as any criterion to ensure sufficient antennaheights so that, in the worst case of refraction (for which k is minimum) thereceiver antenna is not placed in the diffraction region


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Earth Curvature and k factor

One factor for line -of-sight includes earth curvature and the effects of theatmospheric refraction due to the curve of the earths surface

The earths bulge between the end points must be considered whendetermining if LOS and proper path clearance exists, including Fresnelzone

The k factor (refraction index) is a mathematical figure that will helpdetermine the effect on path clearanceNot much of a factor under 10 miles


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Earth Curvature and k factor

One factor for line -of-sight includes earth curvature and the effects of theatmospheric refraction due to the curve of the earths surface

The earths bulge between the end points must be considered whendetermining if LOS and proper path clearance exists, including Fresnelzone

The k factor (refraction index) is a mathematical figure that will helpdetermine the effect on path clearanceNot much of a factor under 10 miles


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Earth Curvature and k factor Effective Earths Radius = k * True Earths Radius True Earths radius= 6371 Km so k=4/3=1.33, standard atmosphere with

normally refracted path (this value should be used whenever local valueis not provided)

Variations of the ray curvature as a function of k True


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Clearance criteria to be satisfied under normal propagation conditions Clearance of 60% or greater at the minimum k suggested for the certain

path Clearance of 100% or greater at k=4/3 In case of space diversity, the antenna can have a 60% clearance at k=4/3

plus allowance for tree growth, buildings (usually 3 meter)


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PET TOPOGR FI

Peta Topografi: peta yang menggambarkan permukaan bumilengkap dengan reliefnya. Penggambaran relief permukaan bumi

ke dalam peta digambar dalam bentuk garis kontur. Garis konturyaitu garis pada peta yang menghubungkan tempat-tempat yangmempunyai ketinggian yang sama.


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PET TOPOGR FI

Sifat-sifat garis kontur pada peta topografi antara lain sebagaiberikut.

a. Semakin rapat jarak antargaris kontur, menunjukansemakin curam daerah tersebut. Begitu juga sebaliknya, bila jarakantargaris konturnya jarang, maka tempat tersebut adalah landai.

b. Bila ditemukan ada garis kontur yang bergigi, hal tersebutmenunjukkan di daerah tersebut terdapat depresi atau lembah. -


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PET TOPOGR FI

radio engineering - line of sight

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