E7E Modulation and demodulation: reactance, phase, and balanced modulators; detectors; mixers

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