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Questions and Answers
What is the formula for calculating power density using transmitted power and distance?
What is the formula for calculating power density using transmitted power and distance?
If the power density at 20 km is 200μW/m^2, how does this relate to the power density at 25 km?
If the power density at 20 km is 200μW/m^2, how does this relate to the power density at 25 km?
What does the attenuation formula ɑ = 10 log 10 (Ҩ1/Ҩ2) dB represent?
What does the attenuation formula ɑ = 10 log 10 (Ҩ1/Ҩ2) dB represent?
What is the range of frequencies designated as Low Frequency?
What is the range of frequencies designated as Low Frequency?
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Which frequency range corresponds to Very High Frequency?
Which frequency range corresponds to Very High Frequency?
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Which statement accurately describes the relationship between electric field intensity and power density?
Which statement accurately describes the relationship between electric field intensity and power density?
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What defines the wavelength of an electromagnetic wave?
What defines the wavelength of an electromagnetic wave?
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What effect does increased humidity or precipitation have on electromagnetic wave absorption?
What effect does increased humidity or precipitation have on electromagnetic wave absorption?
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What is the reflection coefficient?
What is the reflection coefficient?
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At what speed do electromagnetic waves travel in free space?
At what speed do electromagnetic waves travel in free space?
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What propagation mode is associated with frequencies from 3-30 MHz?
What propagation mode is associated with frequencies from 3-30 MHz?
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How does the distance from the source affect magnetic field intensity?
How does the distance from the source affect magnetic field intensity?
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What two components make up an electromagnetic wave?
What two components make up an electromagnetic wave?
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What is the relationship between distance and electromagnetic wave propagation?
What is the relationship between distance and electromagnetic wave propagation?
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Which frequency range is labeled as Ultra High Frequency?
Which frequency range is labeled as Ultra High Frequency?
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What is the relationship between the electric and magnetic components of an electromagnetic wave?
What is the relationship between the electric and magnetic components of an electromagnetic wave?
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What condition must be met for complete reflection to occur?
What condition must be met for complete reflection to occur?
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What is the definition of refraction?
What is the definition of refraction?
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What does Snell's Law relate to?
What does Snell's Law relate to?
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How does the degree of bending of a wave at boundaries behave with frequency?
How does the degree of bending of a wave at boundaries behave with frequency?
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What characterizes diffraction?
What characterizes diffraction?
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What happens during interference?
What happens during interference?
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What is the relationship between sunspot activity and wave propagation?
What is the relationship between sunspot activity and wave propagation?
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How is solar flux defined?
How is solar flux defined?
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What is the correct formula relating wavelength, speed of light, and frequency?
What is the correct formula relating wavelength, speed of light, and frequency?
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Which polarization describes a wave with two unequal components that rotate about the propagation axis?
Which polarization describes a wave with two unequal components that rotate about the propagation axis?
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What is the value of the permeability of free space (μ0)?
What is the value of the permeability of free space (μ0)?
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Which of the following most accurately describes power density?
Which of the following most accurately describes power density?
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What does the inverse square law state about power density?
What does the inverse square law state about power density?
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Which of the following describes vertical polarization?
Which of the following describes vertical polarization?
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What is the value of vacuum permittivity (ε0)?
What is the value of vacuum permittivity (ε0)?
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Which characteristic of electromagnetic waves refers to the propagation direction?
Which characteristic of electromagnetic waves refers to the propagation direction?
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Study Notes
Radiation and Wave Propagation
- Radiation is the loss or escape of energy into free space.
- Wave propagation is the travel of electromagnetic waves through a medium.
- Electromagnetic waves are forms of radiant energy like heat, light, radio, x-ray, and television waves.
- Electromagnetic waves are considered oscillatory disturbances in free space.
Nomenclature of Frequency Bands
- Very Low Frequency (VLF): 3 - 30kHz, Myriametric, Ground Propagation
- Low Frequency (LF): 30 - 300kHz, Kilometric, Ground Propagation
- Medium Frequency (MF): 300 - 3000kHz, Hectometric, Ground Propagation
- High Frequency (HF): 3 - 30MHz, Decametric, Sky Propagation
- Very High Frequency (VHF): 30 - 300MHz, Metric, Space Wave
- Ultra High Frequency (UHF): 300 - 3000MHz, Decimeric, Space Wave
- Super High Frequency (SHF): 3 - 30GHz, Centimeric, Space Wave
- Extreme High Frequency (EHF): 30 - 300GHz, Millimetric, Space Wave
Electromagnetic Wave Characteristic
- Space Time Relationship: An electromagnetic wave has two components: an electric field and a magnetic field. Both vary sinusoidally in time at a fixed point in space and are "in phase".
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Wave Velocity: The speed of electromagnetic waves depends on the medium. In free space, the velocity is:
- c = 3x10^8 m/s
- c = 186,000 statute mi/s
- c = 9.84 x 10^8 ft/s
- Wavelength (λ) is the distance a radio wave travels in one cycle. It is also the spatial separation of two successive oscillations.
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Frequency (f) is the number of cycles per second of a radio wave. It is the rate at which the periodic motion repeats itself.
- λ = c/f
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Polarization refers to the orientation of radiated waves in space.
- Linear Polarization: Electric vector has a specific direction in space.
- Vertical Polarization: Electric vector is vertical, or lies in a vertical plane.
- Horizontal Polarization: Electric vector is horizontal, or lies in a horizontal plane.
- Circular Polarization: Electric vector rotates about the axis of propagation.
- Elliptical Polarization: Electric vector rotates but the amplitudes of its linear components are unequal.
- Random Polarization: No fixed pattern of polarization variation.
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Rays and wavefronts:
- Ray is a line drawn along the direction of wave propagation.
- Wavefront is a surface of constant phase of the wave.
Electromagnetic Quantities and Parameters
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Permeability of free space (μ0): A physical constant used in electromagnetism.
- μ0 = 4π x 10^-7 N/A^2
- Related to the energy stored in a magnetic field.
- C = 1/(√μ0ε0)
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Permittivity of free space (ε0): The absolute dielectric permittivity of classical vacuum.
- ε0 = (1/36π) x 10^-9 F/m
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Power Density (Ρ): The rate at which energy flows through a unit area in space.
- Inverse square law: Ρ is inversely proportional to the square of the distance from the source.
- Ρ = PtGt/(4πd^2) W/m^2
- Where: Pt = transmitted power (W); Gt = gain of transmitting antenna; d = distance from the point source (m)
- Ρ = E^2/377 W/m^2
- Where E = electric field intensity (V/m)
- Ρ = 377H
- Where H = magnetic field intensity (A/m)
- Inverse square law: Ρ is inversely proportional to the square of the distance from the source.
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Electric Field Intensity (E): Directly proportional to the square root of power density and inversely proportional to the distance from the source.
- E = √30Pt/d V/m
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Magnetic Field Intensity (H):
- H = E/377
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Attenuation (α): Due to spherical spreading of the wave (space attenuation). Proportional to the square of the distance traveled.
- α = 10 log 10 (Ρ1/ Ρ2) dB
- Where: Ρ1 = power density at point 1; Ρ2 = power density at point 2
- α = 20 log 10 (d1/ d2) dB
- Where: d1 = distance of point 1 from source; d2 = distance of point 2 from source
Role of Environment on Wave Propagation
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Absorption: Energy from electromagnetic waves is transferred to atoms and molecules in the atmosphere, causing some radio waves to be absorbed.
- Increased humidity, fog, rain, or snow increase absorption.
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Reflection: Occurs at boundaries between materials with different dielectric constants.
- Angle of incidence equals the angle of reflection.
- Complete reflection happens with a perfect conductor when the electric field is perpendicular to the reflecting element.
- Reflection Coefficient: Ratio of the electric intensity of the reflected wave to the incident wave.
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Refraction: Bending of a ray passing from one medium to another at an angle.
- Occurs when electromagnetic waves pass between media with different densities.
- The degree of bending increases with frequency.
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Snell's Law: Describes the relationship between angles of incidence and refraction when waves pass between different media.
- n1 sin 𝜃1 = 𝑛2 sin 𝜃2
- Where: n1= refractive index of incident medium; n2= refractive index of refractive medium; sin 𝜃1= angle of incidence; sin 𝜃2= angle of reflection
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Diffraction: Bending of a wave around an obstacle (an edge, object, or opening).
- Caused by spreading of the wave and interference of different parts of the beam.
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Interference: Occurs when two waves from one source, traveling by different paths, arrive at a point.
- Happens frequently in high-frequency sky waves propagation and microwave space-wave propagation.
Role of the Sun on the Wave
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Sunspots: Grayish-black blemishes on the Sun's surface.
- The 11-year sunspot cycle affects propagation due to the correlation between sunspot activity and ionization.
- Solar Flux: A measure of energy received per unit time, per unit area, per unit frequency interval.
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Description
Test your knowledge on radiation and wave propagation concepts. Explore the various types of electromagnetic waves and their frequency bands. This quiz covers essential definitions and classifications related to electromagnetic radiation and its behavior in different media.
