propagation additional notes
Page 1: Wave Propagation
Learning Objectives
Explain the principles of electromagnetic wave radiation.
Explain radio wave propagation.
Describe the role of frequency allocation and regulatory bodies.
Radiation
Electromagnetic Waves (EM): Move from a point source and spread out.
Oscillation of Charges: Charges vary over time, creating a varying electric field.
Induction of Magnetic Field: A varying electric field induces a varying magnetic field perpendicular to it.
Page 2: Properties of EM Waves
Propagation of EM Waves
Speed: EM waves propagate at the speed of light (3 x 10^8 m/s).
Direction: Propagation is perpendicular to both electric and magnetic field vectors.
Medium Transmission: In mediums, the frequency remains constant, but the travel time to the destination increases.
Polarization
Definition: Direction of the electric field vector varies with time and space, representing electromagnetic wave orientation.
Types of Polarization: 1) Linear Polarization 2) Circular Polarization 3) Elliptical Polarization.
Page 3: Linear Polarization
Characteristics
Description: Electric field remains linear over time; traces a straight path.
Types: 1) X-polarized (along X-axis) 2) Y-polarized (along Y-axis) 3) O-polarized (along N-axis).
Page 4: Circular and Elliptical Polarization
Circular Polarization
Description: Electric field rotates as the wave travels.
Phases: Clockwise and anticlockwise rotation observed.
Elliptical Polarization
Description: Similar to circular but with different magnitudes on axes.
Page 5: Atmospheric Layers and Propagation
Atmosphere Structure
Troposphere: Extends up to 10 km; affects signals above 30 MHz.
Stratosphere: 10-50 km; contains ozone and has temperature increase with height.
Mesosphere: 50-80 km; separation of regions affecting radio signals.
Page 6: Ionosphere
Regions of Ionosphere
Description: Extends from 60-700 km; supports long-distance communication.
Regions: D (60-90 km), E (100-125 km), F1 and F2 layers.
Impact on Signals: Varies during day/night affecting radio transmission.
Page 7: F Region Importance
F Region
Description: Crucial for high-frequency communications; affected by time of day and solar activity.
Nighttime Behavior: Layers merge leading to stable propagation of signals.
Page 8: Propagation Modes
Key Features
Omnidirectional Nature: Radio transmissions don’t require physical alignment of TX & RX.
Frequency Impact: Low frequencies penetrate obstacles better, but higher frequencies suffer more absorption.
Propagation Types: 1) Ground Waves 2) Sky Waves.
Page 9: Sky Wave Propagation
Characteristics
Frequency Range: Effective for frequencies between 2 MHz and 30 MHz.
Mechanism: Signals travel through the sky by reflection from the ionosphere.
Page 10: Ground Wave Propagation
Description
Frequency Range: Effective for frequencies up to 2 MHz.
Characteristics: Signals propagate along the ground, susceptible to losses due to diffraction and absorption.
Page 11: Microwave Propagation
Characteristics
Frequency: Above TV signals, microwaves have small wavelengths and specific transmission requirements.
Limitations: The signal must have an unobstructed line of sight; repeaters can extend the range.
Page 12: Critical Frequency
Definition
Description: Highest frequency that can be reflected back from an ionospheric layer.
Dependence: Related to electron density and angle of incidence.
Page 13: Maximum Usable Frequency (MUF)
Definition
Description: Maximum frequency usable for sky wave communication between two earth points; approximately three times the critical frequency.
Page 14: Skip Distance
Definition
Description: Minimum distance along the earth's surface for sky wave reflection.
Page 15: Reflection, Refraction, and Diffraction
Reflection
Description: Change in direction of waves upon hitting a barrier.
Effects: Can be constructive or destructive.
Refraction
Description: Change in direction as waves move between mediums.
Diffraction
Description: The spreading of waves when encountering obstacles. Common in mobile communications.
Page 16: Polarization Types
Polarization Overview
Types: 1) Linear 2) Circular 3) Elliptical.
Page 17: Noise and Multipath Propagation
Noise
Definition: Unwanted signals affecting radio communication.
Multipath Propagation
Definition: Signals take multiple paths to the receiver; effects can be constructive or destructive.
Page 18: Advanced Propagation Concepts
Factors Influencing Propagation
Topography, Climate, Medium Properties affecting signal transmission.
Page 19: Atmospheric Effects on Propagation
Inversion Layers
Description: Regions where atmospheric conditions differ from standard affecting signal quality.
Page 20: Virtual Height
Description
Definition: Height from which signals appear reflected.
Page 21: Signal Propagation Effects
Effects on Signal
Factors include smoothness, density, topography, climate, and dielectric properties.
Page 22: Reflection and Interference Effects
Reflection
Constructive and Destructive Effects lead to varying signal amplitudes upon reception.
Page 23: Types of Refraction
Variations of Refraction
Simple, Super, and Sub Refraction all affect signal propagation differently.
Page 24: Absorption and Scattering
Absorption
Description: Common on the earth's surface; affects signal strength.
Scattering
Description: Signals directed in various directions upon contact with surfaces.
Page 25: Types of Scattering
Types
Forward Scattering 2) Back Scattering 3) Side Scattering.
Page 26: Further Effects on Signals
Effects Overview
Polarization, Depolarization, Noise, and Multipath Affecting Communication and signal clarity.