Chapter 3 Problems

1. Chapter 3 Problems ECET 214 Prof. Park NJIT

2. Problem 1 Which of the following is not an advantage of a synchronous detection? a. Low distortion b. Eliminate diagonal clipping c. Greater ability to follow fast-modulated signals d. Ability to produce gain

3. Problem 2 The mixer is often referred to as: a. RF amplifier b. oscillator generator c. second detector d. first detector

4. Problem 3 Varactor diodes are used for tuning by: a. capacitance adjustment through a reverse bias diode. b. capacitance adjustment through forward bias. c. temperature compensation of diodes. d. all of the above.

5. Problem 4 In a varactor diode, as voltage increases, capacitance: a. increases b. stays the same c. decreases d. none of the above

6. Problem 5 The only roadblock to having complete receivers on a chip aside from station selection and volume controls is: a. limiting factors of tuned circuits. b. local oscillator. c. mixer circuits. d. IF amplifier.

7. Problem 6 The radio receiver that simply consists of an RF amplifier, detector, and audio amplifier is known as: a. a superheterodyne receiver b. a TRF receiver c. a selective receiver d. a sensitive receiver

8. Problem 7 A receiver’s sensitivity is: a. the extent to which a receiver is capable of differentiating between the desired signal and other signals. b. its ability to drive the output speaker to an acceptable level. c. the ability of the receiver to demodulate a modulated signal. d. the ability of a receiver to attenuate noise signals.

9. Problem 8 A receiver’s selectivity is: a. the extent to which a receiver is capable of differentiating between the desired signal and other signals. b. its ability to drive the output speaker to an acceptable level. c. the ability of the receiver to demodulate a modulated signal. d. the ability of a receiver to attenuate noise signals.

10. Problem 9 If a receiver is overly selective: a. too much noise is picked up and amplified by the receiver. b. only part of the bandwidth of the AM signal is amplified, causing some of the sideband information to be lost and distortion results. c. the tank circuits within the tuned amplifiers have insufficient Q. d. when the volume control is turned up to maximum, the desired station is very weak.

11. Problem 10 If a receiver is underselective: a. only part of the bandwidth of the AM signal is amplified, causing some of the sideband information to be lost and distortion results. b. the tank circuits within the tuned amplifiers have too high a Q. c. when the volume control is turned up to maximum, the desired station is very weak. d. more than one radio station on different frequencies may be picked up by the receiver at the same time.

12. Problem 11 A TRF receiver is to be designed with a single tuned circuit using an 8.2 uH inductor. If the frequency is to be tuned from 550 kHz to 1600 kHz, find the BW that results at 550 kHz if there is exactly 10 kHz BW at a frequency of 1050 kHz. a. 105 kHz b. 15.24 kHz c. 5.24 kHz d. 10 kHz

13. Problem 12 The diode detector: a. is one of the simplest and most effective AM detectors. b. consists of a nonlinear diode and low-pass filter. c. is sometimes referred to as an envelope detector. d. all of the above.

14. Problem 13 Which is not an advantage of diode detectors? a. Power absorbed from the tuned circuit by the diode detector reduces the Q of the tuned circuit. b. They develop a readily usable dc voltage for automatic gain control circuits. c. They are highly efficient. d. Distortion decreases as the amplitude of the AM signal increases.

15. Problem 14 Diagonal clipping: a. occurs if the time constant of the low-pass filter is too large compared to the period of the RF waveform. b. is a type of distortion that occurs with diode detectors. c. is characterized by having the capacitor voltage not follow the full changes of the envelope of the AM waveform. d. all of the above.

16. Problem 15 Synchronous detectors: a. are often called product detectors. b. offer low distortion compared to diode detectors. c. have the ability to provide gain. d. all of the above.

17. Problem 16 The superheterodyne receiver design is superior to the TRF design: a. since it allows for a constant selectivity over the entire tuning range of the receiver. b. since it always uses synchronous detectors instead of diode detectors. c. since it uses many RF amplifier stages before the RF signal is mixed with the local oscillator signal. d. all of the above.

18. Problem 17 An AM signal having a carrier frequency of 560 kHz is to be mixed with a local oscillator signal at a frequency of 1035 kHz. What does the output of the IF amplifier consist of? a. a 455 kHz carrier b. a 475 kHz sinewave c. a 475 kHz AM signal d. the original intelligence signal

19. Problem 18 In Figure 3-1, the output signal of stage (e) is: a. an AM signal with a carrier frequency of 490 kHz. b. an AM signal with a carrier frequency of 1850 kHz. c. a 490 kHz sinewave. d. an 1850 kHz sinewave.

20. Problem 19 In Figure 3-1, the output signal of stage (d) is: a. an AM signal with a carrier frequency of 490 kHz. b. an AM signal with a carrier frequency of 1360 kHz. c. a 490 kHz sinewave. d. a 1 kHz sinewave.

21. Problem 20 In Figure 3-1, the output of stage (a) is: a. an AM signal with a carrier frequency of 1360 kHz. b. an AM signal with a carrier frequency of 1850 kHz. c. a 490 kHz sinewave. d. an 1850 kHz sinewave.

22. Problem 21 In Figure 3-1, the output signal of stage (c) is: a. an AM signal with a carrier signal of 490 kHz. b. an AM signal with a carrier frequency of 1360 kHz. c. a 490 kHz sinewave. d. a 1 kHz sinewave.

23. Problem 22 In Figure 3-1, the receiver design is known as: a. regenerative b. superheterodyne c. TRF d. synchronous

24. Problem 23 In Figure 3-1, the stage sometimes referred to as the first detector is: a. stage a b. stage b c. stage c d. stage d

25. Problem 24 In Figure 3-1, the stages that contain tuned circuits are: a. stages a, b and d. b. stages a, b and c. c. stages a, d and e. d. stages a, c and d.

26. Problem 25 In Figure 3-1, the stages that must contain nonlinear devices are: a. stages a, b and c. b. stages a and e. c. stages b and d. d. stages b and c.

27. Problem 26 In Figure 3-1, the image frequency would be: a. 980 kHz b. 2340 kHz c. 1850 kHz d. 870 kHz

28. Problem 27 A padder capacitor: a. is placed in series with the tank inductor to provide tracking at the low end of a large frequency band. b. is placed in parallel with each section of the ganged capacitors of the tank to provide tracking at the high end of a large frequency band. c. is placed in an RF amplifier to provide for proper neutralization. d. is placed in a tank circuit to provide for electronic tuning.

29. Problem 28 A trimmer capacitor: a. is placed in series with the tank inductor to provide tracking at the low end of a large frequency band. b. is placed in parallel with each section of the ganged capacitor of the tank to provide tracking at the high end of a large frequency band. c. is placed in an RF amplifier to provide for proper neutralization. d. is placed in a tank circuit to provide for electronic tuning.

30. Problem 29 A varicap: a. is placed in series with the tank inductor to provide tracking at the low end of a large frequency band. b. is placed in parallel with each section of the ganged capacitors of the tank to provide tracking at the high end of a large frequency band. c. is placed in an RF amplifier to provide for proper neutralization. d. is placed in a tank circuit to provide for electronic tuning.

31. Problem 31 Image frequency rejection on a standard AM broadcast band receiver is not a major problem since: a. the image frequency is not close to the IF frequency. b. the image frequency is not close to the LO frequency. c. the image frequency is not produced by mixing action. d. the image frequency is so far away from the RF amplifier stage’s tuned frequency.

32. Problem 32 Which of the following is not a major benefit of using RF amplifier stages in superheterodyne receiver design? a. improved image frequency rejection b. larger frequency tuning range c. more gain resulting in improved sensitivity d. improved noise characteristics

33. Problem 33 Which of the following is not an advantage of FETs over BJTs in RF amplifier usage? a. Their input impedance does not load down the Q of the circuit preceding the FET stage. b. The availability of dual gate FETs provides an isolated injection point for the AGC. c. Their input/output square-law relationship allows for lower distortion levels. d. They have improved image frequency rejection.

34. Problem 34 An autodyne mixer is: a. a stage that provides the mixing and generates the LO at the same time. b. a mixer that uses a dual-gate FET. c. a mixer that automatically provides for AGC action. d. a stage that mixes the LO with the AM signal without the use of a transistor.

35. Problem 35 In a superheterodyne receiver the bulk of the receiver’s sensitivity and selectivity is due to the: a. RF amplifier stages. b. converter stages. c. IF amplifier stages. d. local oscillator.

36. Problem 36 Double conversion is: a. a receiver design that uses two superheterodyne receivers to receive a weak signal. b. a technique used to reduce image frequency problems in a superheterodyne receiver. c. a technique used to solve the TRF tuning problems. d. a method that ensures that a superheterodyne receiver does not break into oscillations due to stray positive feedback.

37. Problem 37 The circuit of Figure 3-2 is an example of: a. an RF mixer, local oscillator, and IF filter b. an autodyne mixer c. a receive converter d. all of the above

38. Problem 38 In Figure 3-2, the tank circuit made up of L1 and C1 is tuned at: a. the IF frequency. b. the LO frequency. c. the RF carrier frequency. d. the image frequency.

39. Problem 39 In Figure 3-2, the tank circuit made up of L4 and C4 is tuned at: a. the IF frequency. b. the LO frequency. c. the RF carrier frequency. d. the image frequency.

40. Problem 40 In Figure 3-2, the tank circuit made up of L5 and C5 is tuned at: a. the IF frequency. b. the LO frequency. c. the RF carrier frequency. d. the image frequency.

41. Problem 41 In Figure 3-2, the purpose of C3 is: a. to determine the frequency of oscillation of the LO. b. to couple the local oscillator frequency from the tank circuit to be amplified by Q1. c. to act as a bypass capacitor for R3. d. to neutralize the RF amplifier stage.

42. Problem 42 The AGC control voltage: a. is actually the dc voltage component produced by the mixing action in the AM demodulator stage. b. varies as the signal strength of the received signal varies. c. is a negative feedback voltage. d. is produced by an RC circuit having a much larger time constant than that of the detector. e. all of the above.

44. Problem 43 In Figure 3-3, the tank circuit made up of L1, A, and B is tuned to: a. the LO frequency. b. the RF carrier frequency. c. the IF frequency. d. the image frequency.

45. Problem 44 In Figure 3-3, the tank circuit made up of L4, C, and D is tuned to: a. the LO frequency. b. the RF carrier frequency. c. the IF frequency. d. the image frequency.

46. Problem 45 In Figure 3-3, the tank circuit inside of T1 is tuned to: a. the LO frequency. b. the RF carrier frequency. c. the IF frequency. d. the image frequency.

47. Problem 46 In Figure 3-3, the transistor Q1 is used as: a. the nonlinear device in an RF mixer stage. b. the active part of an RF amplifier. c. the active part of an LO stage. d. all of the above.

48. Problem 47 In Figure 3-3, the transistor Q2 is used as: a. an RF mixer stage transistor. b. an IF amplifier stage transistor. c. a detector transistor. d. an audio amplifier stage transistor.

49. Problem 48 In Figure 3-3, the transistor Q3 is used as: a. an RF mixer stage transistor. b. an IF amplifier stage transistor. c. a detector transistor. d. an audio amplifier stage transistor.

50. Problem 49 In Figure 3-3, the transistor Q4 is used as: a. an RF mixer stage transistor. b. an IF amplifier stage transistor. c. a detector transistor. d. an audio amplifier stage transistor.