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Questions and Answers
Radio wave propagation refers to the transmission of electromagnetic waves in free space.
Radio wave propagation refers to the transmission of electromagnetic waves in free space.
True
AM and FM systems are not commonly used in wireless communication.
AM and FM systems are not commonly used in wireless communication.
False
A microphone converts an electrical signal into an acoustical signal.
A microphone converts an electrical signal into an acoustical signal.
False
A stable crystal oscillator is used in FM transmitters to generate the carrier frequency.
A stable crystal oscillator is used in FM transmitters to generate the carrier frequency.
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The final power amplifier in a transmitter circuit is usually a class A amplifier.
The final power amplifier in a transmitter circuit is usually a class A amplifier.
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The modulation process in FM transmitters is similar to that in AM transmitters.
The modulation process in FM transmitters is similar to that in AM transmitters.
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Frequency multipliers in FM transmitters can increase the frequency up to 5 times the fundamental frequency.
Frequency multipliers in FM transmitters can increase the frequency up to 5 times the fundamental frequency.
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An antenna is an active device that can amplify electromagnetic waves.
An antenna is an active device that can amplify electromagnetic waves.
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The frequency multiplier decreases the frequency deviation of the modulating signal.
The frequency multiplier decreases the frequency deviation of the modulating signal.
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Electromagnetic waves can propagate through free space without being guided.
Electromagnetic waves can propagate through free space without being guided.
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The angle of reflection for radio waves is different from that of light waves.
The angle of reflection for radio waves is different from that of light waves.
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Refraction of radio waves occurs because of the bending of waves as they travel through different media.
Refraction of radio waves occurs because of the bending of waves as they travel through different media.
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Diffraction refers to the signal being blocked entirely by obstacles.
Diffraction refers to the signal being blocked entirely by obstacles.
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Ground wave is another name for surface wave.
Ground wave is another name for surface wave.
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The presence of tall structures does not affect the propagation of electromagnetic waves.
The presence of tall structures does not affect the propagation of electromagnetic waves.
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A poor conductor surface would reflect all the wave energy from radio waves.
A poor conductor surface would reflect all the wave energy from radio waves.
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Ground waves are radio signals that have a frequency of 30 kHz to 3 MHz.
Ground waves are radio signals that have a frequency of 30 kHz to 3 MHz.
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The propagation of ground waves is independent of the conductivity of the Earth's surface.
The propagation of ground waves is independent of the conductivity of the Earth's surface.
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Sky waves can be refracted back to the Earth's surface after interacting with the ionosphere.
Sky waves can be refracted back to the Earth's surface after interacting with the ionosphere.
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The frequency range for sky waves is from 3 MHz to 30 MHz.
The frequency range for sky waves is from 3 MHz to 30 MHz.
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The angle of refraction of sky waves increases as they reach higher layers of the ionosphere.
The angle of refraction of sky waves increases as they reach higher layers of the ionosphere.
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Space waves propagate through free space using a method known as Radio Frequency Modulation (RFM).
Space waves propagate through free space using a method known as Radio Frequency Modulation (RFM).
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A single hop of a sky wave can travel up to 2000 miles before reaching the receiver.
A single hop of a sky wave can travel up to 2000 miles before reaching the receiver.
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Skip zones are areas where signals can be received during sky wave propagation.
Skip zones are areas where signals can be received during sky wave propagation.
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The formula for horizon distance is given by $d=\sqrt{2h}$
The formula for horizon distance is given by $d=\sqrt{2h}$
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Fading in radio wave propagation refers to the variation in signal amplitude at the receiver end due to signal path characteristics.
Fading in radio wave propagation refers to the variation in signal amplitude at the receiver end due to signal path characteristics.
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Multipath fading is also known as ‘Rayleigh Fading’.
Multipath fading is also known as ‘Rayleigh Fading’.
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The height of the transmitter antenna does not affect the distance between the transmitter and receiver.
The height of the transmitter antenna does not affect the distance between the transmitter and receiver.
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Shadow fading occurs due to obstacles between the transmitter and receiver.
Shadow fading occurs due to obstacles between the transmitter and receiver.
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The systematic variation in distance between the transmitter and antenna contributes to signal fading.
The systematic variation in distance between the transmitter and antenna contributes to signal fading.
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When a radio signal reflects off surfaces, it always improves the signal's strength.
When a radio signal reflects off surfaces, it always improves the signal's strength.
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The term ‘horizon distance’ is used to describe the maximum distance a signal can travel without any obstacles.
The term ‘horizon distance’ is used to describe the maximum distance a signal can travel without any obstacles.
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Study Notes
Radio Wave Propagation
- Radio waves are electromagnetic waves that travel in free space
- AM and FM systems are common methods of wireless communication using radio waves to transmit information over long distances
- A simple transmitter uses an oscillator connected to an antenna to produce a high-frequency carrier wave that radiates in free space
- A more practical AM transmitter also includes a carrier oscillator, buffer amplifier, final power amplifier, driver, microphone, audio amplifier, speech processor, and modulation amplifier
AM Transmitter Block Diagram
- Shows the components and their function in a typical AM transmitter
- The oscillator generates the carrier frequency
- The microphone converts audio signals into electrical signals, amplified by the audio amplifier
- The modulation amplifier combines the audio signal with the carrier wave
- The final power amplifier boosts the power of the modulated signal ready for transmission
FM Transmitter Block Diagram
- Similar components to AM, but with a different modulation process
- Uses a crystal oscillator to generate a carrier frequency
- Frequency multipliers can increase the frequency up to 5 times, altering the modulation index of FM
- The phase modulator combines the audio signal with the carrier wave
Characteristics of Electromagnetic Waves
- Radiated waves propagate through free space
- Several factors affect wave propagation, including atmospheric conditions, time of day, frequency, trees, buildings, and other structures
Optical Characteristics of Radio Waves - Reflection
- Reflection of radio waves is analogous to light wave reflection
- The angle of reflection equals the angle of incidence
- A perfect conductor reflects all incident radio waves
- A poor conductor absorbs and reflects some wave energy
Optical Characteristics of Radio Waves - Refraction
- Refraction is the bending of radio waves
- The degree of bending depends on the refractive index of the medium
- Illustrated using ionized air, air, and the phenomenon of the bending of radio waves at the boundary
Optical Characteristics of Radio Waves - Diffraction
- Diffraction is the bending of waves around objects
- Based on Huygens' principle
- Radio wave encounters an obstacle creates a "shadow zone"
Types of Radio Wave Propagation - Ground Wave
- Also known as surface waves
- Travel along the Earth's surface
- Affected by the conductivity of the Earth's surface; better on saltwater surfaces, poorer on low moisture surfaces
Types of Radio Wave Propagation - Sky Wave
- Propagates through the ionosphere, being bent back to its destination point
- The direction and angle of bending depend on the ionization level of the ionosphere layers (Snell's Law)
- Sky waves can have multiple reflections (hops) before reaching the destination, traveling up to 2,000 miles
- Skip zone is the area that does not receive the signal during sky wave propagation
Types of Radio Wave Propagation - Space Wave
- Propagates through free space following a straight line path (Line of Sight (LOS))
- Commonly used in VHF and UHF spectrum
- The distance between the transmitter and receiver (D) depends on the height of the antennas involved
- (d) is the horizon distance = √(2h_t) ; (D) more practical distance = √(2h_t) + √(2h_r)
Problems in Radio Wave Propagation - Fading
- Fluctuation in signal amplitude at the receiver due to characteristics of the signal path
- Environmental conditions (variations in distance, presence of multi-path signals), relative motion between transmitter/receiver ("shadow fading") cause fading
Problems in Radio Wave Propagation - Multipath
- Signal arrives at the receiver from different paths (straight, reflected, refracted)
- This leads to a significant delay in arrival time at the receiver and a differing phase angle
- Decrease in signal power is the result also known as Rayleigh Fading
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Description
This quiz explores the principles of radio wave propagation and the workings of AM and FM transmitters. Learn about the components of a typical AM transmitter and understand how audio signals are converted for wireless communication. Test your knowledge on the essential elements involved in the process of radio wave transmission.
