69 lines
3.2 KiB
Markdown
69 lines
3.2 KiB
Markdown
E7E Modulation and demodulation: reactance, phase, and balanced modulators; detectors; mixers
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- [[E7E01]] (B)
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Which of the following can be used to generate FM phone signals? #card
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- [[A.]] Balanced modulation of the audio amplifier
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- [[B.]] Reactance modulation of a local oscillator
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- [[C.]] Reactance modulation of the final amplifier
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- [[D.]] Balanced modulation of a local oscillator
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- [[E7E02]] (D)
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What is the function of a reactance modulator? #card
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- [[A.]] Produce PM or FM signals by varying a resistance
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- [[B.]] Produce AM signals by varying an inductance
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- [[C.]] Produce AM signals by varying a resistance
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- [[D.]] Produce PM or FM signals by varying a capacitance
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- [[E7E03]] (D)
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What is a frequency discriminator? #card
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- [[A.]] An FM generator circuit
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- [[B.]] A circuit for filtering closely adjacent signals
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- [[C.]] An automatic band-switching circuit
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- [[D.]] A circuit for detecting FM signals
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- [[E7E04]] (A)
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What is one way to produce a single-sideband phone signal? #card
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- [[A.]] Use a balanced modulator followed by a filter
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- [[B.]] Use a reactance modulator followed by a mixer
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- [[C.]] Use a loop modulator followed by a mixer
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- [[D.]] Use a product detector with a DSB signal
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- [[E7E05]] (D)
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What is added to an FM speech channel to boost the higher audio frequencies? #card
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- [[A.]] A de-emphasis network
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- [[B.]] A harmonic enhancer
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- [[C.]] A heterodyne enhancer
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- [[D.]] A pre-emphasis network
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- [[E7E06]] (A)
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Why is de-emphasis used in FM communications receivers? #card
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- [[A.]] For compatibility with transmitters using phase modulation
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- [[B.]] To reduce impulse noise reception
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- [[C.]] For higher efficiency
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- [[D.]] To remove third-order distortion products
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- [[E7E07]] (B)
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What is meant by the term “baseband” in radio communications? #card
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- [[A.]] The lowest frequency band that the transmitter or receiver covers
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- [[B.]] The frequency range occupied by a message signal prior to modulation
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- [[C.]] The unmodulated bandwidth of the transmitted signal
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- [[D.]] The basic oscillator frequency in an FM transmitter that is multiplied to increase the deviation and carrier frequency
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- [[E7E08]] (C)
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What are the principal frequencies that appear at the output of a mixer? #card
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- [[A.]] Two and four times the input frequency
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- [[B.]] The square root of the product of input frequencies
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- [[C.]] The two input frequencies along with their sum and difference frequencies
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- [[D.]] 1.414 and 0.707 times the input frequency
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- [[E7E09]] (A)
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What occurs when the input signal levels to a mixer are too high? #card
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- [[A.]] Spurious mixer products are generated
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- [[B.]] Mixer blanking occurs
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- [[C.]] Automatic limiting occurs
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- [[D.]] Excessive AGC voltage levels are generated
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- [[E7E10]] (A)
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How does a diode envelope detector function? #card
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- [[A.]] By rectification and filtering of RF signals
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- [[B.]] By breakdown of the Zener voltage
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- [[C.]] By mixing signals with noise in the transition region of the diode
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- [[D.]] By sensing the change of reactance in the diode with respect to frequency
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- [[E7E11]] (C)
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Which type of detector is used for demodulating SSB signals? #card
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- [[A.]] Discriminator
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- [[B.]] Phase detector
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- [[C.]] Product detector
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- [[D.]] Phase comparator
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