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Questions and Answers
What is the bandwidth used for a TV system?
Which frequency band ranges from 30 to 300 MHz?
Which type of noise is caused by natural atmospheric processes?
Exceeding which frequency leads to the experience of Cosmic Noise?
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Which frequency band is also known as the decimeter band?
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What is the frequency range classified as Very Low Frequency?
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Which frequency band ranges from 3 GHz to 30 GHz?
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What causes Thermal Noise?
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What is the primary purpose of modulation in communication systems?
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What is demodulation primarily used for in communication systems?
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Which of the following is NOT a reason for modulation-demodulation processes?
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What happens in Amplitude Modulation (AM)?
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Which element is responsible for converting input signals into suitable electrical signals?
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In a basic communication system, what is the function of the communication channel?
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What type of noise is involved in a communication system?
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Which modulation technique involves varying the frequency of the carrier signal?
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Study Notes
Radio Frequency Bands
- Radio frequency (RF) is a range of frequencies from 3 kHz to 300 GHz.
- RF corresponds to the frequency of radio waves and alternating current that carry signals.
- Frequency bands are specific ranges within the RF spectrum.
- The wavelength of a radio wave decreases with an increase in frequency.
Very Low Frequency (VLF)
- Frequency: 3 kHz to 30 kHz
- Wavelength: 10 to 100 km
Low Frequency (LF)
- Frequency: 30 kHz to 300 kHz
- Wavelength: 1 to 10 km
- Also known as the kilometer band or kilometer wave.
Medium Frequency (MF)
- Frequency: 300 kHz to 3 MHz
- Wavelength: 100 to 1000 m
- Also known as the hectometer band or hectometer wave.
- MF follows ground wave and sky wave propagation.
High Frequency (HF)
- Frequency: 3 MHz to 30 MHz
- Wavelength : 10 to 100 m
- Also known as the decameter band or decameter wave.
Very High Frequency (VHF)
- Frequency: 30 MHz to 300 MHz
- Wavelength: 1 to 10 m
Ultra High Frequency (UHF)
- Frequency: 300 MHz to 3 GHz
- Wavelength: 10 to 100 cm
- Also known as the decimeter band or decimeter wave.
Super High Frequency (SHF)
- Frequency: 3 GHz to 30 GHz
- Wavelength: 1 to 10 cm
- Also known as the centimeter band or centimeter wave.
Extremely High Frequency (EHF)
- Frequency: 30 GHz to 300 GHz
- Wavelength: 10 to 100 mm
- Also known as the millimeter band or millimeter wave.
Bandwidth
- Bandwidth is the range of frequencies within a given band that is used for signal transmission.
- AM System: 30 kHz
- FM System: 200 kHz
- TV System: 6 MHz
Electrical Noise
- Electrical noise can disrupt signal transmission.
- Noise can be internal or external.
External Noise
- Man-made: Caused by external sources such as powerlines and ignition systems.
- Atmospheric: Caused by natural atmospheric processes.
- Solar Noise: Originates from the sun, caused by things like corona discharges and sunspots.
- Cosmic Noise: Experienced at frequencies above 15 MHz when antennas are pointed toward the sun or other regions of the sky like the Milky Way Galaxy.
Internal Noise
- Thermal Noise: Caused by the random motion of electrons within components such as resistors, speakers, microphones, and antennas.
- Thermal Noise increases with absolute temperature.
Modulation and Demodulation
- Modulation is the process of combining a low-frequency signal (audio signal) with a high-frequency signal (carrier signal) for efficient transmission.
- Demodulation is the process of separating the original audio signal from the carrier signal.
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Why is Modulation-Demodulation needed?
- To improve transmission efficiency by using a higher frequency carrier signal which allows the signal to travel longer distances with less attenuation.
- To reduce antenna size by using the carrier signal's wavelength to create a smaller and more efficient antenna.
- To enable frequency multiplexing by sharing the same transmission medium with multiple signals at different frequencies.
- To increase the effective radiated power by using the carrier signal's energy to amplify the original signal.
The Carrier Signal
- The mathematical equation for the carrier signal is: eC = Em Sin (ωt + θ ), where:
- Em represents the amplitude of the carrier signal.
- ωt represents the angular frequency of the carrier signal.
- θ represents the phase angle of the carrier signal.
Types of Modulation
- Amplitude Modulation (AM): The amplitude of the carrier signal is varied in accordance with the audio signal.
- Frequency Modulation (FM): The frequency of the carrier signal is varied in accordance with the audio signal.
- Phase Modulation (PM): The phase angle of the carrier signal is varied in accordance with the audio signal.
Block Diagram of a Basic Communication System
- A basic communication system consists of:
- Input Transducer: Converts information into an electrical signal.
- Transmitter: Modulates the electrical signal onto the carrier signal.
- Communication Channel: The medium through which the modulated signal travels.
- Receiver: Demodulates the signal to extract the original information.
- Output Transducer: Converts the electrical signal back to its original form (e.g. sound, image).
Noise
- Noise is an unwanted electrical signal that can be added to the transmitted signal during transmission.
- It can be natural or man-made.
- It degrades the quality of the received signal.
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Description
This quiz covers the various radio frequency bands including Very Low Frequency (VLF), Low Frequency (LF), Medium Frequency (MF), High Frequency (HF), Very High Frequency (VHF), and Ultra High Frequency (UHF). Learn about their frequency ranges and corresponding wavelengths in the RF spectrum. Test your understanding of radio waves and their classifications.
