This is the Multiple Choice Questions in Chapter 6: Receivers from the book Electronic Communication Systems by Roy Blake
Start Practice Exam Test Questions
Choose the letter of the best answer in each questions.
MULTIPLE CHOICE
1. The two basic specifications for a receiver are:
- a. the sensitivity and the selectivity
- b. the number of converters and the number of IFs
- c. the spurious response and the tracking
- d. the signal and the noise
ANS: A
2. The superheterodyne receiver was invented by:
- a. Foster
- b. Seeley
- c. Armstrong
- d. Hertz
ANS: C
3. Trimmers and padders are:
- a. two types of adjusting tools
- b. small adjustable resistors
- c. small adjustable inductors
- d. small adjustable capacitors
ANS: D
4. "Skin effect" refers to:
- a. the way radio signals travel across a flat surface
- b. the tissue-burning effect of a strong RF signal
- c. the increase of wire resistance with frequency
- d. none of the above
ANS: C
5. The "front end" of a receiver can include:
- a. the tuner
- b. the RF amplifier
- c. the mixer
- d. all of the above
ANS: D
6. "IF" stands for:
- a. intermediate frequency
- b. intermodulation frequency
- c. indeterminate frequency
- d. image frequency
ANS: A
7. AGC stands for:
- a. Audio Gain Control
- b. Automatic Gain Control
- c. Active Gain Control
- d. Active Gain Conversion
ANS: B
8. The frequency of the local oscillator:
- a. is above the RF frequency
- b. is below the RF frequency
- c. can be either above of below the RF frequency
- d. is fixed, typically at 455 kHz.
ANS: C
9. The local oscillator and mixer are combined in one device because:
- a. it gives a greater reduction of spurious responses
- b. it increases sensitivity
- c. it increases selectivity
- d. it is cheaper
ANS: D
10. Basically, sensitivity measures:
- a. the weakest signal that can be usefully received
- b. the highest-frequency signal that can be usefully received
- c. the dynamic range of the audio amplifier
- d. none of the above
ANS: A
11. Basically, selectivity measures:
- a. the range of frequencies that the receiver can select
- b. with two signals close in frequency, the ability to receive one and reject the other
- c. how well adjacent frequencies are separated by the demodulator
- d. how well the adjacent frequencies are separated in the mixer
ANS: B
12. When comparing values for shape factor:
- a. a value of 1.414 dB is ideal
- b. a value of 0.707 is ideal
- c. a value of 1.0 is ideal
- d. there is no ideal value
ANS: C
13. When comparing values for shape factor:
- a. a value of 2 is better than a value of 4
- b. a value of 4 is better than a value of 2
- c. both values are basically equivalent
- d. none of the above
ANS: A
14. Distortion in a receiver can occur in:
- a. the mixer
- b. the detector
- c. the IF amplifiers
- d. all of the above
ANS: D
15. Phase distortion is important in:
- a. voice communications systems
- b. color video receivers
- c. monochrome video receivers
- d. all of the above
ANS: B
16. The response of a receiver to weak signals is usually limited by:
- a. the AGC
- b. noise generated in the receiver
- c. the dynamic range of the receiver
- d. the type of detector circuit being used
ANS: B
17. Image frequencies occur when two signals:
- a. are transmitted on the same frequency
- b. enter the mixer, with one being a reflected signal equal to the IF frequency
- c. enter the mixer, one below and one above the local oscillator by a difference equal to the IF
- d. enter the mixer, and the difference between the two signals is equal to twice the IF
ANS: C
18. An image must be rejected:
- a. prior to mixing
- b. prior to IF amplification
- c. prior to detection
- d. images cannot be rejected
ANS: A
19. Image frequency problems would be reduced by:
- a. having an IF amplifier with the proper shape factor
- b. having a wideband RF amplifier after the mixer
- c. having a narrowband RF amplifier before the mixer
- d. none of the above
ANS: C
20. A common AM detector is the:
- a. PLL
- b. envelope detector
- c. ratio detector
- d. all of the above
ANS: B
21. An FM detector is the:
- a. PLL
- b. ratio detector
- c. quadrature detector
- d. all of the above
ANS: D
22. Germanium diodes are used in AM detectors because:
- a. they are faster than silicon diodes
- b. they are cheaper than silicon diodes
- c. they minimize distortion from nonlinearity
- d. all of the above
ANS: C
23. A common SSB detector is:
- a. a PLL
- b. a diode
- c. a BFO
- d. a product detector
ANS: D
24. BFO stands for:
- a. Beat Frequency Oscillator
- b. Barrier Frequency Oscillator
- c. Bipolar Frequency Oscillator
- d. Bistable Frequency Oscillator
ANS: A
25. To demodulate both SSB and DSBSC, you need to:
- a. use a Foster-Seeley discriminator
- b. reinject the carrier
- c. use double conversion
- d. use one diode for SSB and two diodes for DSBSC
ANS: B
26. Which would be best for DSBSC:
- a. carrier detection
- b. coherent detection
- c. envelope detection
- d. ratio detection
ANS: B
27. An FM detector that is not sensitive to amplitude variations is:
- a. Foster-Seeley detector
- b. a quadrature detector
- c. a PLL detector
- d. all of the above
ANS: C
28. The function of a limiter is:
- a. to remove amplitude variations
- b. to limit spurious responses
- c. to limit dynamic range
- d. to limit noise response
ANS: A
29. Suppressing the audio when no signal is present is called:
- a. AGC
- b. squelch
- c. AFC
- d. limiting
ANS: B
30. LNA stands for:
- a. Limited-Noise Amplifier
- b. Low-Noise Amplifier
- c. Low-Noise Audio
- d. Logarithmic Noise Amplification
ANS: B
31. AFC stands for:
- a. Audio Frequency Compensator
- b. Autodyne Frequency Compensation
- c. Automatic Frequency Control
- d. Autonomous Frequency Control
ANS: C
32. The function of AFC is:
- a. maintain a constant IF frequency
- b. match the local oscillator to the received signal
- c. lock the discriminator to the IF frequency
- d. none of the above
ANS: B
33. SAW stands for:
- a. Symmetrical Audio Wave
- b. Surface Acoustic Wave
- c. Silicon-Activated Wafer
- d. Software-Activated Wave
ANS: B
34. The important property of a SAW is:
- a. it stabilizes the audio in a receiver
- b. it allows software radios to be built
- c. it is a stable bandpass filter
- d. none of the above
ANS: C
35. The main function of the AGC is to:
- a. keep the gain of the receiver constant
- b. keep the gain of the IF amplifiers constant
- c. keep the input to the detector at a constant amplitude
- d. all of the above
ANS: C
36. DSP stands for:
- a. Dynamic Signal Properties
- b. Direct Signal Phase
- c. Distorted Signal Packet
- d. Digital Signal Processor
ANS: D
37. SINAD stands for:
- a. Sinusoidal Amplitude Distortion
- b. Signal and Noise Amplitude Distortion
- c. Signal-plus-Noise-to-Noise Ratio
- d. Signal-plus-Noise and Distortion-to-Noise and Distortion Ratio
ANS: D
38. TRF stands for:
- a. Tuned Radio Frequency
- b. Tracking Radio Frequency
- c. Transmitted Radio Frequency
- d. Tuned Receiver Function
ANS: A
COMPLETION
1. Almost all modern receivers use the _________________________ principle.
ANS: superheterodyne
2. The first radio receiver of any kind was built in the year ____________________.
ANS: 1887
3. When two tuned circuits ____________________ each other, it means that when the frequency of one is adjusted, the other changes with it.
ANS: track
4. The ____________________ effect causes the resistance of wire to increase with frequency.
ANS: skin
5. The superhet was invented in the year ____________________.
ANS: 1918
6. In a receiver, the ____________________ refers to the input filter and RF stage.
ANS: front end
7. In a superhet, the output of the ____________________ goes to the IF amplifiers.
ANS: mixer
8. In a superhet, the ____________________ frequency is the difference between the local oscillator frequency and the received signal frequency.
ANS:
intermediate
IF
9. The ____________________ circuit adjusts the gain of the IF amplifiers in response to signal strength.
ANS: AGC
10. An ____________________ converter uses the same transistor for both the local oscillator and the mixer.
ANS: autodyne
11. In low-side injection, the local oscillator is ____________________ than the received signal frequency.
ANS: lower
12. ____________________ is the ability of a receiver to separate two signals that are close to each other in frequency.
ANS: Selectivity
13. ____________________ is the ability of a receiver to receive and successfully demodulate a very weak signal.
ANS: Sensitivity
14. A receiver with two different IF frequencies is called a double-____________________ receiver.
ANS: conversion
15. A multiple-conversion receiver will have better rejection of ____________________ frequencies.
ANS: image
16. A demodulator is also called a ____________________.
ANS: detector
17. An ____________________ detector uses a diode to half-wave rectify an AM signal.
ANS: envelope
18. A ____________________ detector is used for SSB signals.
ANS: product
19. A BFO produces a locally generated ____________________.
ANS: carrier
20. A DSBSC signal requires a ____________________ detection circuit.
ANS: coherent
21. FM detectors have a characteristic ____________________-shaped curve.
ANS: S
22. While still commonly found, the Foster-Seeley and ratio detectors are ____________________.
ANS: obsolescent
23. Unlike the PLL detector, the quadrature detector is sensitive to changes in ____________________ of the input signal.
ANS: amplitude
24. A dual-____________________ MOSFET is useful for AGC.
ANS: gate
25. Diode mixers are too ____________________ to be practical in most applications.
ANS: noisy
26. The IF amplifiers in an AM receiver must be Class ____________________.
ANS: A
27. A double-tuned IF transformer is usually ____________________ coupled for the response to have a flat top and steep sides.
ANS: over
28. Multiple IF stages can be ____________________-tuned to increase the bandwidth.
ANS: stagger
29. Compared to tuned circuits, ceramic and crystal IF filters do not require ____________________.
ANS: adjustment
30. Up-conversion is when the output of the mixer is a ____________________ frequency than the incoming signal.
ANS: higher
31. In a block converter, the frequency of the first local oscillator is ____________________.
ANS:
fixed
constant
32. Typically, AGC reduces the gain of the ____________________ amplifiers.
ANS: IF
33. An ____________________-meter is designed to indicate signal strength in many communications receivers.
ANS: S
34. The effectiveness of FM ____________________ is measured by a receiver’s quieting sensitivity.
ANS: limiting
35. A ____________________ refers to any kind of FM or PM detector.
ANS: discriminator
SHORT ANSWER
1. Suppose the bandwidth of a tuned circuit is 10 kHz at 1 MHz. Approximately what bandwidth would you expect it to have at 4 MHz?
ANS:20 kHz
2. Using high-side injection for a 1-MHz IF, what is the frequency of the local oscillator when the receiver is tuned to 5 MHz?
ANS:
6 MHz
3. An IF filter has a –60 dB bandwidth of 25 kHz and a –6 dB bandwidth of 20 kHz. What is the shape factor value?
ANS:
1.25
4. Suppose a receiver uses a 5-MHz IF frequency. Assuming high-side injection, what would be the image frequency if the receiver was tuned to 50 MHz?
ANS:
60 MHz
5. Suppose a SSB receiver requires an injected frequency of 1.5 MHz. What would be the acceptable frequency range of the BFO if the maximum acceptable baseband shift is 100 hertz?
ANS:
1.5 MHz ± 100 hertz
6. The transformer of a double-tuned IF amplifier has a Q of 25 for both primary and secondary. What value of kc do you need to achieve optimal coupling?
ANS:
0.06
7. What value of transformer coupling would a double-tuned 10-MHz IF amplifier with optimal coupling need to get a bandwidth of 100 kHz?
ANS:
0.01
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