Online Questions and Answers Topic Outline
- MCQs in Amplitude Modulation
- MCQs in Phase Modulation
- MCQs in Sound Pressure Level
- MCQs in Frequency Modulation
- MCQs in Pulse Modulation
MCQs in Modulation Series
Following is the list of multiple choice questions in this brand new series:
Continue Practice Exam Test Questions Part XVI of the Series
751. _________ are frequency-dependent circuits designed to produce an output voltage that is proportional to the instantaneous frequency at its output
- a. PM receivers
- b. PM demodulators
- c. FM demodulators
- d. FM receivers
752. Increasing the reverse bias on a varactor diode will it cause its capacitance to
- a. decrease
- b. increase
- c. remains the same
- d. drop to zero
753. The capacitance of a varactor diode is in what general range?
- a. pF
- b. nF
- c. uF
- d. F
754. Which of the following is the simplest form of tuned-circuit frequency discriminator?
- a. Foster-Seeley discriminator
- b. Ratio detector
- c. slope detector
- d. PLL detector
755. It is simply two single-ended slope detectors connected in parallel and fed 180 degrees out phase.
- a. Foster-Seeley discriminator
- b. quadrature detector
- c. balanced slope generator
- d. PLL detector
756. The frequency change in crystal oscillator produced by a varactor diode is
- a. zero
- b. small
- c. medium
- d. large
757. A phase modulator varies the phase shift of the
- a. carrier
- b. modulating signal
- c. modulating voltage
- d. sideband frequency
758. Which of the following tuned-circuit frequency discriminator is relatively immune to amplitude variations in its input signal?
- a. ratio detector
- b. slope detector
- c. balanced slope detector
- d. quadrature detector
759. In FM demodulators, it is also called coincidence detector
- a. quadrature demodulator
- b. PLL demodulator
- c. Foster-Seely discriminator
- d. ratio detector
760. The widest phase variation is obtained with ________.
- a. RC low-pass filter
- b. RC high-pass filter
- c. LR low-pass filter
- d. LC resonant circuit
761. An FM receiver provides 100dB of voltage gain prior to the limiter. Calculate the receiver's sensitivity if the limiter's quieting for an FM receiver is 300 mV?
- a. 4.5 uV
- b. 3.0 uV
- c. 2.1 uV
- d. 1.3 uV
762. The small frequency change produced by a phase modulator can be increased by using ___________.
- a. amplifier
- b. mixer
- c. frequency multiplier
- d. frequency divider
763. In FM receiver, limiters produce a constant-amplitude output of all signals above a prescribed minimum input level called _________.
- a. threshold voltage
- b. capture level
- c. quieting level
- d. any of these
764. The inherent ability of FM to diminish the effects of interfering signals is called _______.
- a. capture effect
- b. noise suppression
- c. adjacent channel rejection
- d. non of these
765. A crystal oscillator whose frequency can be changed by an input voltage is called _______.
- a. VCO
- b. VXO
- c. VFO
- d. VHF
766. Which oscillators are preferred for carrier generators because of their good frequency stability?
- a. LC
- b. RC
- c. LR
- d. crystal
767. Which of the following frequency demodulators requires an input limiter?
- a. Foster-Seely discriminator
- b. Pulse-averaging discriminator
- c. quadrature detector
- d. PLL
768. Provides a slight automatic control over the local oscillator circuit and compensates for its drift that would otherwise cause a station to become detuned.
- a. AGC
- b. AFC
- c. VVC
- d. VCO
769. ________ of an FM receiver is the maximum dB difference signal strength between two received signals necessary for the capture effect to suppress the weaker signal.
- a. capture effect
- b. capture gain
- c. capture ratio
- d. capture loss
770. When two limiter stages are used, there is called ___________.
- a. double limiting
- b. two-time limiting
- c. reserve limiting
- d. ratio limiting
771. Which discriminator averages pulses in a low-pass filter?
- a. ratio detector
- b. PLL
- c. quadrature detector
- d. pulse-averaging discriminator
772. Which of the frequency demodulator is considered the best overall?
- a. ratio detector
- b. PLL
- c. quadrature
- d. pulse-averaging discriminator
773. One of the prominent advantage of FM over PM is
- a. FM requires frequency multipliers to increase the modulation index and frequency deviation to useful levels
- b. the voltage controlled oscillators of FM can be directly modulated and produce outputs with high frequency deviations and high modulation
- c. the modulation index of FM is independent of the modulating signal frequency
- d. FM offers better signal-to-noise performance than PM
774. What special speaker is used for low frequency?
- a. baffle
- b. base
- c. tweeter
- d. woofer
775. Each speaker assembly at the receiver reproduces exactly the same information
- a. monophonic
- b. multiphonic
- c. stereophonic
- d. any of these
776. In a pulse averaging discriminator, the pulse are produced by a(n)
- a. astable multivibrator
- b. zero-crossing detector
- c. one-shot
- d. low-pass filter
777. A reactance modulator looks like a capacitance of 35pF in parallel with the oscillator-tuned circuit whose inductance is 50 uH and capacitance is 40 pF. What is the center frequency of the oscillator prior to FM?
- a. 1.43 MHz
- b. 2.6 MHz
- c. 3.56 MHz
- d. 3.8 MHz
778. The frequency of an SCA channel subcarrier is _______.
- a. 38 kHz
- b. 15 kHz
- c. 67 kHz
- d. 53 kHz
779. The L-R stereo channel in FM broadcasting is between
- a. 50 Hz to 15 kHz
- b. 60 kHz to 74 kHz
- c. 23 kHz to 53 kHz
- d. 20 Hz to 20 kHz
780. An FM demodulator that uses a differential amplifier and tuned circuits to convert frequency variations into voltage variations is the
- a. quadrature detector
- b. Foster-Seeley discriminator
- c. differential peak detector
- d. phase-locked loop
781. The output amplitude of the phase detector in a quadrature detector is proportional to
- a. pulse width
- b. pulse frequency
- c. input amplitude
- d. the phase shift value at center
782. The output to a PLL is 2MHz. In order for the PLL to be locked. The VCO output must be
- a. 0 MHz
- b. 1 MHz
- c. 2 MHz
- d. 4 MHz
783. With stereo transmission, the maximum frequency deviation is
- a. 75 kHz
- b. 15 kHz
- c. 25 kHz
- d. 3 kHz
784. The L + R stereo channel occupies _________.
- a. 50 Hz to 15 kHz
- b. 60 kHz to 74 kHz
- c. 23 kHz to 53 kHz
- d. 20 Hz to 20 kHz
785. The band of frequencies over which a PLL will acquire or recognize an input signal is called the
- a. circuit bandwidth
- b. capture range
- c. band of acceptance
- d. lock range
786. The three primary frequency bands are allocated by FCC for two-way FM radio communications except:
- a. 132 MHz to 174 MHz
- b. 450 MHz to 470 MHz
- c. 806 MHz to 947 MHz
- d. 1026 MHz to 1035 MHz
787. The maximum frequency deviation for two-way transmitters is typically
- a. 25 kHz
- b. 5 kHz
- c. 75 kHz
- d. 3 kHz
788. Decreasing the input frequency to be locked PLL will cause the VCO output to
- a. decrease
- b. increase
- c. remains constant
- d. jump to the free-running frequency
789. The range of frequencies over which a PLL will track input signal variations is known as the
- a. circuit bandwidth
- b. capture range
- c. band of acceptance
- d. lock range
790. The maximum modulating signal frequency for two-way transmitter is typically
- a. 3 kHz
- b. 5 kHz
- c. 15 kHz
- d. 75 kHz
791. Over a narrow range of frequencies, the PLL acts like a
- a. low-pass filter
- b. bandpass filter
- c. tunable oscillator
- d. frequency modulator
792. The output of a PLL frequency demodulator is taken from the
- a. low-pass filter
- b. VCO
- c. phase detector
- d. none of these
793. The primary advantage of FM over AM
- a. capture effect
- b. noise immunity
- c. FM can use class C amplifiers
- d. FM is more efficient
794. The usual cutoff frequency of pre-emphasis and de-emphasis in broadcast FM?
- a. 50 Hz
- b. 75 Hz
- c. 2122 Hz
- d. 3183 Hz
795. The maximum deviation for narrowband FM?
- a. 2500
- b. 5
- c. 1.67
- d. 75
796. Which of the following is best frequency demodulator in use?
- a. Foster-Seeley discriminator
- b. ratio detector
- c. slope detector
- d. PLL
797. The range of frequencies over which the PLL will capture an input signal is known as ________.
- a. lock range
- b. capture range
- c. bandwidth
- d. sidebands
798. Type of FM demodulator that is widely used in TV audio demodulators
- a. ratio detector
- b. quadrature detector
- c. PLL
- d. pulse-averaging discriminator
799. A variation of Foster-Seeley discriminator widely used in older TV receiver designs
- a. ratio detector
- b. PLL
- c. quadrature detector
- d. crosby modulator
800. The range of frequencies over which a PLL will track an input is called
- a. lock range
- b. capture range
- c. track range
- d. driving range
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