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Note of Radio propagation by Minakshi Das

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Lecture Slide 4 Unit 2: Radio Propagation EL324: Mobile Communication 6th Semester, B.Tech

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Topics • Basic propagation • Propagation models • Mechanisms of radio propagation • Large scale and small scale fading • dB unit • Free space propagation model • Two Ray Ground Reflection model

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Basics - Propagation • Radio waves are • • • • • • Easy to generate Can travel long distances Can penetrate buildings They are both used for indoor and outdoor communication They are omni-directional: can travel in all directions They can be narrowly focused at high frequencies (greater than 100MHz) using parabolic antennas (like satellite dishes) • Properties of radio waves are frequency dependent • At low frequencies, they pass through obstacles well, but the power falls off sharply with distance from source • At high frequencies, they tend to travel in straight lines and bounce off obstacles (they can also be absorbed by rain) • They are subject to interference from other radio wave sources 3

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Basics - Propagation At VLF, LF, and MF bands, radio waves follow the ground. AM radio broadcasting uses MF band reflection Ionosphere At HF bands, the ground waves tend to be absorbed by the earth. The waves that reach ionosphere (100-500km above earth surface), are refracted and sent back to earth. absorption 4

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