RADIO RECEIVERS Questions and Answers :-
1. Indicate which of the following statements about the advantages of the phase discriminator over the slope detector is false:
A. Much easier alignment
B. Better linearity
C. Greater limiting
D. Fewer tuned circuits
ANSWER: C
2. Show which of the following statements about the amplitude limiter is untrue:
A. The circuit is always biased in class C, by virtue of the leak-type bias.
B. When the input increases past the threshold of the limiting, the gain
decreases to keep the output constant.
C. The output must be tuned
D. Leak-type bias must be used
ANSWER: A
3. In a radio receiver with simple AGC
A. an increase in signal strength produces more AGC
B. the audio stage gain is normally controlled by the AGC
C. the faster the AGC time constant the more accurate the output
D. the highest AGC voltage is produced
ANSWER: A
4. In a broadcast superheterodyne receiver, the
A. local oscillator operates below the signal frequency
B. mixer input must be tuned to the signal frequency
C. local oscillator frequency is normally double the IF
D. RF amplifier normally works at 455 kHz above the carrier frequency
ANSWER: B
5. To prevent overloading of the IF amplifier in a receiver, one should use
A. squelch
B. variable sensitivity
C. variable selectivity
D. double conversion
ANSWER: B
6. A superheterodyne receiver with an IF of 450 kHz is tuned to a signal at 1200 kHz. The image frequency is
A. 750 kHz
B. 900 kHz
C. 1650 kHz
D. 2100 kHz
ANSWER: D
7. In a ratio detector
A. the linearity is worse than in phase discriminator
B. stabilization against signal strength variations is provided
C. the output is twice that obtainable from a similar phase discriminator
D. the circuit is the same as in a discriminator, except that the diodes are reversed
ANSWER: A
8. The typical squelch circuit cuts off
A. an audio amplifier when the carrier is absent
B. RF interference when the signal is weak
C. An IF amplifier when the AGC is maximum
D. An IF amplifier when the AGC is minimum
ANSWER: A
9. Indicate the false statement in connection with communications receivers.
A. The noise limiter cuts off the receiver’s output during a noise pulse.
B. A product demodulator could be used for the reception of Morse code.
C. Double conversion is used to improve image rejection
D. Variable sensitivity is used to eliminate selective fading
ANSWER: D
10. The controlled oscillator synthesizer is sometimes preferred over the direct one because
A. it is a simpler piece of equipment
B. its frequency stability is better
C. it does not require crystal oscillator
D. it is relatively free of spurious frequency
ANSWER: D
11. The frequency generated by each decade in a direct frequency synthesizer is much higher than the frequency shown; this is done to
A. reduce the spurious frequency problem
B. increase the frequency stability of the synthesizer
C. reduce the number of decades
D. reduce the number of crystals required
ANSWER: A
12. Indicate which of the following circuits could not demodulate SSB:
A. Balance modulator
B. Product modulator
C. BFO
D. Phase discriminator
ANSWER: D
13. If a FET is used as the first AF amplifier in a transistor receiver, this will have the effect of
A. improving the effectiveness of the AGC
B. reducing the effect of negative-peak clipping
C. reducing the effect of noise at low modulation depths
D. improving the selectivity of the receiver
ANSWER: B
14. Indicate the false statement. The superheterodyne receiver replaced the TRF receiver because the latter suffered from
A. gain variation over the frequency coverage range
B. insufficient gain and sensitivity
C. inadequate selectivity at high frequencies
D. instability
ANSWER: B
15. The image frequency of a superheterodyne receiver
A. is created within the receiver itself
B. is due to insufficient adjacent channel rejection
C. is not rejected be the IF tuned circuits
D. is independent of the frequency to which the receiver is tuned
ANSWER: C
16. One of the main functions of the RF amplifier in a superheterodyne receiver is to
A. provide improved tracking
B. permit better adjacent-channel rejection
C. increase the tuning range of the receiver
D. improve the rejection of the image frequency
ANSWER: D
17. A receiver has poor IF selectivity. It will therefore also have poor
A. blocking
B. double-spotting
C. diversion reception
D. sensitivity
ANSWER: A
18. Three-point tracking is achieved with
A. variable selectivity
B. the padder capacitor
C. double spotting
D. double conversion
ANSWER: B
19. The local oscillator of a broadcast receiver is tuned to a frequency higher than the incoming frequency
A. to help the image frequency rejection
B. to permit easier tracking
C. because otherwise an intermediate frequency could not be produced
D. to allow adequate frequency coverage without switching
ANSWER: D
20. If the intermediate frequency is very high (indicate false statement)
A. image frequency rejection is very good
B. the local oscillator need not be extremely stable
C. the selectivity will be poor
D. tracking will be improved
ANSWER: D
21. A low ratio of the ac to the dc load impedance of a diode detector results in
A. diagonal clipping
B. poor AGC operation
C. negative-peak clipping
D. poor AF response
ANSWER: C
22. One of the following cannot be used to demodulate SSB:
A. Product detector
B. Diode Balance modulator
C. Bipolar transistor balanced modulator
D. Complete phase-shift generator
ANSWER: C
23. Indicate the false statement. Noting that no carrier is transmitter with J3E, we see that
A. the receiver cannot use a phase comparator for AFC
B. adjacent-channel rejection is more difficult
C. production of AGC is a rather complicated process
D. the transmission is not compatible with A3E
ANSWER: B
24. When a receiver has good blocking performance, this means that
A. it does not suffer from double-spotting
B. its image frequency rejection is poor
C. it is unaffected by AGC derived from nearby transmissions
D. its detector suffers from burnout
ANSWER: B
25. An AM receiver uses a diode detector for demodulation. This enables it satisfactorily to receive
A. single-sideband, suppressed-carrier
B. single-sideband, reduced-carrier
C. ISB
D. Single-sideband, full-carrier
ANSWER: D