Microwave Communication Systems Overview
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Questions and Answers

Which component in a microwave radio receiver is responsible for restoring the baseband signal's original characteristics?

  • Microwave oscillator
  • Deemphasis network (correct)
  • Channel separation network
  • FM demodulator

    • What process is used to translate IF frequencies to RF frequencies in microwave generators?

  • Heterodyning (correct)
  • Up-conversion via mixing (correct)
  • Multiplying frequencies
  • Filtering through a bandpass filter

    • What is the typical range of intermediate frequency (IF) carrier frequencies in microwave systems?

  • 40 MHz to 60 MHz
  • 100 MHz to 120 MHz
  • 60 MHz to 80 MHz (correct)
  • 20 MHz to 40 MHz

    • What significantly influences the location of intermediate repeater sites in microwave communication?

    <p>Nature of the terrain</p> Signup and view all the answers

    What type of repeater receives, amplifies, reshapes, and retransmits the signal at RF frequencies?

    <p>RF-to-RF repeater</p> Signup and view all the answers

    What is the average path (hop) length assumed during preliminary route planning for microwave systems?

    <p>25 miles to 35 miles</p> Signup and view all the answers

    Which component in a microwave radio system amplifies and filters the RF frequencies?

    <p>Bandpass filter</p> Signup and view all the answers

    During what frequency range can local rainfall patterns significantly influence path length?

    <p>Above 10 GHz</p> Signup and view all the answers

    What is the primary advantage of using microwave radio systems compared to other communication systems?

    <p>They can carry large quantities of information due to high frequencies.</p> Signup and view all the answers

    Which of the following is a disadvantage of microwave radio communication?

    <p>Limited to line-of-sight applications due to straight-line propagation.</p> Signup and view all the answers

    Which modulation technique is primarily used in microwave radio systems?

    <p>Frequency Modulation (FM)</p> Signup and view all the answers

    What role does the pre-emphasis network serve in an FM microwave transmitter?

    <p>It provides an artificial boost in amplitude to higher baseband frequencies.</p> Signup and view all the answers

    In microwave radio communication, which signal characteristics make FM signals preferable?

    <p>Insensitivity to nonlinear distortion and lower sensitivity to random noise.</p> Signup and view all the answers

    What is a significant operational benefit of microwave radio systems related to maintenance?

    <p>Increased reliability and less maintenance required.</p> Signup and view all the answers

    Which factor can complicate the analysis and design of microwave radio circuits?

    <p>Difficulty in implementing conventional resistive components.</p> Signup and view all the answers

    What types of baseband signals can modulate the FM carrier in microwave radio systems?

    <p>A composite of voice-band channels, video, and data.</p> Signup and view all the answers

    What is the range of frequencies for microwaves?

    <p>500 MHz to 300 GHz</p> Signup and view all the answers

    What is the formula to calculate the wavelength of microwaves?

    <p>$λ=c/f$</p> Signup and view all the answers

    In microwave communication systems, what modulation technique is used for multiplexing?

    <p>Frequency division multiplexing</p> Signup and view all the answers

    What is the typical operating distance for terrestrial microwave radio relay systems?

    <p>15 miles to 4000 miles</p> Signup and view all the answers

    Which of the following channels might a microwave communication system support?

    <p>More than 22,000 channels</p> Signup and view all the answers

    What is the function of using low and high bands in microwave communication systems?

    <p>To allow full-duplex operation</p> Signup and view all the answers

    What type of modulation techniques are commonly used in microwave communication?

    <p>Pulse code modulation and time division multiplexing</p> Signup and view all the answers

    What is the primary characteristic of microwave radios in communication systems?

    <p>They propagate signals through Earth’s atmosphere.</p> Signup and view all the answers

    Study Notes

    Microwave Communication Systems

    • Characterized as electromagnetic waves with frequencies ranging from 500 MHz to 300 GHz, with wavelengths between 1 cm and 60 cm (slightly longer than infrared energy).
    • Wavelength can be calculated using the formula: λ = c/f, where:
      • λ is the wavelength (in meters, m)
      • c is the speed of light (approximately 3 x 10^8 m/s)
      • f is the frequency (in Hertz, Hz)
    • Each frequency band is divided in half for full-duplex operation, with the lower half designated as the low band and the upper half as the high band.
    • Since the mid-1980s, the majority of electronic communication systems use digital modulation techniques for voice, video, and data transmission.
    • Terrestrial microwave radio relay systems using frequency modulation (FM) or digitally modulated carriers (PSK or QAM) provide about 35% of the total information-carrying circuit mileage in the United States.
    • Operating distances vary from 15 miles to 4000 miles.
    • System capacities range from less than 12 voice-band channels to more than 22,000 channels.
    • Modulation Techniques:
      • Frequency Modulation (FM) - Frequency Division Multiplexing (FDM)
      • Pulse Code Modulation (PCM) - Time Division Multiplexing (TDM)
      • Digital Modulation Techniques - Phase Shift Keying (PSK) and Quadrature Amplitude Modulation (QAM)

    Advantages of Microwave Radio

    • Requires minimal land acquisition for each station.
    • High operating frequencies allow for large information transmission capacity.
    • Short wavelengths enable the use of relatively small antennas.
    • Radio signals effectively propagate around obstacles like water and mountains.
    • Fewer repeaters are needed for signal amplification, reducing distances between switching centers and minimizing underground facilities.
    • Minimal delay times and crosstalk between voice channels.
    • Increased reliability and reduced maintenance requirements.

    Disadvantages of Microwave Radio

    • Challenging to analyze and design microwave frequency circuits, leading to difficulties in measurement techniques and implementation of conventional circuit components.
    • Transient time is crucial in microwave frequencies, often requiring specialized components.
    • Straight-line propagation limits use to line-of-sight applications.

    Components of a Microwave Communication System

    Microwave Transmitter

    • Baseband: The composite signal modulating the FM carrier can consist of one or more of the following:
      • Frequency-division-multiplexed voice-band channels
      • Time-division-multiplexed voice-band channels
      • Broadcast-quality composite video or picturephone
      • Wideband data
    • Pre-emphasis Network: Enhances the amplitude of higher baseband frequencies.
    • FM Deviator: Modulates the IF carrier, which will become the main microwave carrier.
    • IF Carrier: Typically ranges between 60 MHz and 80 MHz.
    • Mixer, Microwave Oscillator, and Bandpass Filter: Up-convert the IF and its sidebands to the microwave region.
    • Microwave Generator: Comprises a crystal oscillator and a series of frequency multipliers.

    Microwave Receiver

    • Channel Separation Network: Isolates and filters incoming microwave channels, directing them to individual receivers.
    • Bandpass Filter, AM Mixer, and Microwave Oscillator: Down-convert the RF microwave frequencies to IF frequencies.
    • FM Demodulator: A noncoherent FM detector (discriminator or PLL demodulator).
    • Deemphasis Network: Restores the original amplitude-versus-frequency characteristics of the baseband signal.

    Microwave Repeater

    • Essentially a receiver and transmitter placed back-to-back or in tandem.
    • Amplifies and reshapes received signals before retransmitting them.
    • Types:
      • IF - Heterodyne Repeater: Down-converts the received RF carrier to IF, amplifies, reshapes, up-converts to RF, and retransmits.
      • Baseband Repeater: Down-converts the RF carrier to IF, amplifies, filters, and further demodulates to baseband.
      • RF-to-RF Repeater: Directly amplifies and retransmits the received RF carrier.

    Microwave Repeater Placement

    • Locations influenced by terrain and path length.
    • Path lengths typically range from 25 miles to 35 miles between stations.
    • Transmitter output power and antenna gain also factor into site selection.
    • Line-of-sight path clearance and received signal strength are primary determinants of distance.
    • Rainfall patterns can significantly affect path length for frequencies above 10 GHz.

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    Related Documents

    Microwave System Module 2 PDF

    Description

    Explore the principles of microwave communication systems, characterized by electromagnetic waves in the frequency range of 500 MHz to 300 GHz. This quiz covers wavelength calculation, full-duplex operation, and digital modulation techniques crucial for modern communication. Test your knowledge on how these systems support voice, video, and data transmission.

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