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    Principle of Communication by Frenzel Chapter 4

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    jerson eyas
    1. Amplitude modulation circuits generate AM by either varying the gain of an amplifier or attenuation of a voltage divider according to the modulating signal, or by applying the product of the carrier and modulating signals to a nonlinear component. 2. Basic AM detectors include half wave rectifiers and synchronous detectors which use an internal clock signal to switch the AM signal on and off, producing rectification. 3. Balanced modulators generate double sideband signals and filters must have high selectivity, with crystal filters most commonly used but digital signal processing is increasing. Product detectors generate the mathematical product of the sideband signal and carrier to demodulate amplitude shift keying or single sideband signals.

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    Principle of Communication by Frenzel Chapter 4

    Uploaded by

    jerson eyas
    210 views2 pages
    1. Amplitude modulation circuits generate AM by either varying the gain of an amplifier or attenuation of a voltage divider according to the modulating signal, or by applying the product of the carrier and modulating signals to a nonlinear component. 2. Basic AM detectors include half wave rectifiers and synchronous detectors which use an internal clock signal to switch the AM signal on and off, producing rectification. 3. Balanced modulators generate double sideband signals and filters must have high selectivity, with crystal filters most commonly used but digital signal processing is increasing. Product detectors generate the mathematical product of the sideband signal and carrier to demodulate amplitude shift keying or single sideband signals.

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    Principle of Communication by frenzel Chapter 4

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    1. Amplitude modulation circuits generate AM by either varying the gain of an amplifier or attenuation of a voltage divider according to the modulating signal, or by applying the product of the carrier and modulating signals to a nonlinear component. 2. Basic AM detectors include half wave rectifiers and synchronous detectors which use an internal clock signal to switch the AM signal on and off, producing rectification. 3. Balanced modulators generate double sideband signals and filters must have high selectivity, with crystal filters most commonly used but digital signal processing is increasing. Product detectors generate the mathematical product of the sideband signal and carrier to demodulate amplitude shift keying or single sideband signals.

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    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
    210 views2 pages

    Principle of Communication by Frenzel Chapter 4

    Uploaded by

    jerson eyas
    1. Amplitude modulation circuits generate AM by either varying the gain of an amplifier or attenuation of a voltage divider according to the modulating signal, or by applying the product of the carrier and modulating signals to a nonlinear component. 2. Basic AM detectors include half wave rectifiers and synchronous detectors which use an internal clock signal to switch the AM signal on and off, producing rectification. 3. Balanced modulators generate double sideband signals and filters must have high selectivity, with crystal filters most commonly used but digital signal processing is increasing. Product detectors generate the mathematical product of the sideband signal and carrier to demodulate amplitude shift keying or single sideband signals.

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    of 2

    One type of AM circuit varies the gain of the amplifier or the attenuation of the voltage divider according

    to the modulating signal plus 1. Another applies the product of the carrier and modulating signals to a
    nonlinear component or circuit. A parallel tuned circuit resonant at the carrier frequency, with a
    bandwidth wide enough to filter out the modulating signal as well as the second and higher harmonics of
    the carrier, can be used to produce an AM wave.

    Low-level AM can be produced by many types of circuits. In high-level modulation, the modulator varies
    the voltage and power in the transmitter's final RF amplifier stage.

    Demodulator (detector) circuits accept a modulated signal and recover the original modulating
    information. The basic AM detector is a half wave rectifier. Synchronous detectors use an internal clock
    signal to switch the AM signal off and on, producing rectification.
    A balanced modulator is a circuit that generates a DSB signal. The diode ring or lattice modulator is a
    widely used balanced modulator.
    Filters used to generate SSB signals must have high selectivity. Crystal filters are the most common but
    DSP is becoming more widely used.
    Product detectors, which are circuits for demodulating or detecting DSB or SSB signals, generate the
    mathematical product of the SSB signal and the carrier.

    QUESTION--------------------------------------------------------------------------------------------

    1. What mathematical operation does an amplitude modulator perform?


    multiplication
    2. A device that produces amplitude modulation must have what type of response curve?
    square-law response curve
    3. Describe the two basic ways in which amplitude modulator circuits generate AM.
    One technique used to produce AM is to have the modulating signal vary the gain or attenuation
    of a linear circuit through which the carrier is passed or linearly mix the carrier modulating signal
    and apply them to a non linear circuit with a square law response.
    4. What type of semiconductor device gives a near-perfect square-law response?
    diode
    5. Which four signals and frequencies appear at the output of a low-level diode modulator?
    Carrier, modulating signal, upper and lower sidebands
    6. What component does a PIN diode appear to be when it is used in an amplitude modulator?
    A voltage variable resistor
    7. Name the primary application of PIN diodes as amplitude modulators.
    Pin diodes are used to form variable attenuators to generate AM
    8. What kind of amplifier must be used to boost the power of a low-level AM signal?
    Linear
    9. How does a differential amplifier modulator work?
    A differential amplifier multiplies the voltage difference between two inputs (Vin+ - Vin-) by
    some constant factor Ad, the differential gain. It may have either one output or a pair of outputs
    where the signal of interest is the voltage difference between the two outputs.
    10. To what stage of a transmitter does the modulator connect in a high-level AM transmitter?
    11. What is the simplest and most common technique for demodulating an AM signal?
    Use a half wave rectifier diode detector
    12. What is the most critical component value in a diode detector circuit? Explain.
    The filter capacitor across the load in a diodedetector must have a value that is high enough to
    filter out the carrier frequency but low enough so that it does not distort the recovered lower
    frequency information signal
    13. What is the basic component in a synchronous detector? What operates this component?
    14. What signals does a balanced modulator generate? Eliminate?
    Upper and lower sidebands are generated but eliminates or suppresses the carrier

    15. What type of balanced modulator uses transformers and diodes?


    Lattice modulator
    16. What is the most commonly used filter in a filter-type SSB generator?
    Crystal filter
    17. What is the most difficult part of producing SSB for voice signals by using the phasing methods?
    18. Which type of balanced modulator gives the greatest carrier suppression?
    19. What is the name of the circuit used to demodulate an SSB signal?
    20. What signal must be present in an SSB demodulator besides the signal to be detected?

    PROBLEM----------------------------------------------------------------------------------

    1. A collector modulated transmitter has a supply voltage of 48 V and an average collector current of 600
    mA. What is the input power to the transmitter? How much modulating signal power is needed to
    produce 100 percent modulation?

    2. An SSB generator has a 9-MHz carrier and is used to pass voice frequencies in the 300- to 3300-Hz
    range. The lower sideband is selected. What is the approximate enter frequency of the filter needed to
    pass the lower sideband?

    3. A 1496 IC balanced modulator has a carrier-level input of 200 mV. The amount of suppression
    achieved is 60 dB. How much carrier voltage appears at the output?

    CRITICAL THINKING--------------------------------------------------------
    1. State the relative advantages and disadvantages of synchronous detectors versus other types of
    amplitude demodulators.
    2. Could a balanced modulator be used as a synchronous detector? Why or why not?
    3. An SSB signal is generated by modulating a 5-MHz carrier with a 400-Hz sine tone. At the receiver,
    the carrier is reinserted during demodulation, but its frequency is 5.00015 MHz rather than exactly 5
    MHz. How does this affect the recovered signal? How would a voice signal be affected by a carrier that
    is not exactly the same as the original?

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