ECT261 Final Examination Practice

Instructions: There are 50 questions on this test. It is written in a style very similar to the REAL final exam. Choose the best answer from among those given. Click the GRADE button on the bottom of the form when you want the exam graded.

Note: You can practice this test as many times as you desire; the system will cook you up a fresh batch of questions each time you access this page.

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1. Which of these describes demodulation?

a) Recovering information from a carrier wave
b) Placing information onto a carrier wave
c) Controlling the frequency of a carrier wave
d) None of the above

2. A certain transmitter's antenna is 1/4 wavelength long and measures 29.528 inches. What is the actual operating frequency of this transmitter? (1 inch = 2.54 cm).

a) 25 MHz
b) 50 MHz
c) 100 MHz
d) None of the above

3. What is the wavelength of a 600 MHz signal?

a) 1 Meter
b) 0.5 Meter (50 cm)
c) 0.75 Meter
d) None of the above

4. The signal shown above is fed into a bandpass filter with a center frequency of 1 KHz. What will the output of the bandpass filter look like on an oscilloscope?

a) A 1 KHz square wave
b) A 1 KHz sine wave
c) A 2 KHz triangle wave
d) None of the above

5. The frequency-domain picture of an electronic signal is called a:

a) Spectrogram
b) Oscillogram
c) Noise Plot
d) None of the above

6. What is the only "pure" waveform containing no harmonic energies?

a) Triangle wave
b) Sine wave
c) Square wave
d) None of the above

7. Which type of noise is caused by the thermal agitation of charge carriers within a conductor?

a) Atmospheric noise
b) Cosmic noise
c) Johnson noise
d) None of the above

8. Which of these could be classified as an external noise source?

a) Shot Noise
b) Atmospheric noise
c) Flicker Noise
d) None of the above

9. What noise voltage will be generated across a 100K resistor at room temperature (24 degrees Celsius) if the circuit's bandwidth is 1 MHz? (k=1.38 x 10-23 J/K)

a) 40.5 uV
b) 0.5 uV
c) 20 uV
d) None of the above

10. What is the information frequency in the AM signal pictured above?

a) 1 KHz
b) 2 KHz
c) 4 KHz
d) 5 KHz

11. If the load resistance RL is 50 Ohms, what is the total power of the AM signal above?

a) 200 Watts
b) 204 Watts
c) 250 Watts
d) None of the above

12. What bandwidth will be required to transmit a 2 KHz sine-wave tone on an AM carrier wave if the carrier frequency is 118 MHz?

a) 10 KHz
b) 4 KHz
c) 8 KHz
d) None of these

13. An AM transmitter is operating on a carrier frequency (Fc) of 10.000 MHz, with 5000 volts of carrier (Vc). The transmitter is operating at 70% modulation. What is the voltage in the upper side band?

a) 3500 V
b) 2750 V
c) 2000 V
d) 1750 V

14. What bandwidth will be required to transmit a 5 KHz sine-wave tone on an AM carrier wave if the carrier frequency is 710 KHz?

a) 10 KHz
b) 5 KHz
c) 1 KHz
d) None of the above

15. To isolate a transmitter's carrier oscillator from undesired load changes, what stage is often used?

a) A buffer amplifier
b) A class C amplifier
c) A power amplifier
d) None of the above

16. A certain high-level transmitter produces 10 Watts of carrier power. How much power must the audio amplifier produce to 100% modulate this transmitter?

a) 2 Watts
b) 4 Watts
c) 8 Watts
d) 5 Watts
e) None of the above

17. Where does the modulation take place at in a low-level transmitter?

a) At the oscillator
b) At the final power amplifier
c) At the buffer amplifier
d) Before the final power amplifier

18. What is meant by the term "dead-keyed?"

a) The unmodulated condition; 0% modulation
b) 50% modulated
c) 100% modulated; maximum output power
d) None of the above

19. The oscillator in a certain transmitter produces +6 dBm of output. The signal is subsequently amplified in the following stages:

Buffer: +10 dB
Modulator: +6 dB
Driver: +10 dB
Final: +14 dB
Antenna Coupler: -1 dB
What is the final output power of this transmitter in Watts?

a) 8 Watts
b) 32 Watts
c) 400 mW
d) None of these

20. Why would the power supply to an oscillator stage be regulated?

a) To provide maximum power output from the oscillator
b) To prevent the oscillator from producing a distorted sine wave
c) To prevent the oscillator from being "pulled" off frequency
d) None of the above

21. In order for an oscillator to start, the loop gain must be:

a) Greater than 1
b) Greater than or equal to 1
c) Less than 1
d) None of the above

22. What type of oscillator is pictured above?

a) Colpitts
b) Hartley
c) Armstrong
d) Pierce
e) None of the above

23. Which of these devices would provide the most stable oscillation frequency?

a) An RC time-constant
b) An LC resonant circuit
c) A quartz crystal
d) A ceramic resonator

24. Another name for the series-resonant frequency of a crystal is the:

a) Pole
b) Zero
c) Maximum
d) Minimum

25. A certain crystal has the following characteristics: Ls=1 H, Cs=.001 pF, Rs = 150 Ohms, Cm = 5 pF. At series-resonance, what is the approximate terminal impedance of the unit?

a) 30 + j125 Ohms
b) 30 - j150 Ohms
c) 150 Ohms (Equal to Rs)
d) Infinity (Open Circuit)

26. A certain crystal has the following characteristics: Ls=1 H, Cs=.001 pF, Rs = 150 Ohms, Cm = 5 pF. What is the parallel-resonant frequency of the unit?

a) 5.032921 MHz
b) 4.986123 MHz
c) 5.033424 MHz
d) None of the above

27. A certain crystal has the following characteristics: Ls=1 H, Cs=.001 pF, Rs = 150 Ohms, Cm = 5 pF. At parallel-resonance, what is the approximate terminal impedance of the unit?

a) 30 + j125 Ohms
b) 30 - j150 Ohms
c) 150 Ohms (Equal to Rs)
d) Infinity (Open Circuit)

28. A certain crystal has the following characteristics: Ls=1 H, Cs=.001 pF, Rs = 150 Ohms, Cm = 5 pF. What is the series-resonant frequency of the unit?

a) 5.032921 MHz
b) 4.986123 MHz
c) 5.033424 MHz
d) None of the above

29. What is the advantage of having a constant-frequency amplifier (the IF amplifier) in a superheterodyne receiver?

a) The gain can be held constant
b) The noise is minimized
c) The bandwidth will be constant
d) None of these

30. The two signal components that are produced in a diode-type AM detector circuit are:

a) The upper and lower sidebands
b) A DC level and the AC information signal
c) The carrier frequency and sidebands
d) None of these

31. The purpose of the frequency converter section of a superhet receiver is to:

a) Keep the output level at the speaker constant, regardless of input signal level changes
b) Eliminate the image response
c) Prevent local oscillator frequency drift
d) None of these

32. What is meant by the term "high-side injection?"

a) The local oscillator operates with a large AC output signal
b) The IF amplifier uses negative-bias to produce AGC
c) The local oscillator operates above the frequency of the RF carrier
d) None of the above

33. What is the function of the preselector in a superhet receiver?

a) Boosts the gain of the IF amplifier
b) Used to produce the AGC control signal
c) Eliminates the image frequency
d) None of these

34. Which section of a superhet receiver determines the receiver's bandwidth?

a) Detector
b) Preselector
c) IF Amplifier
d) None of these

35. What frequency should be at TP "B" above if N=1, R=10, F1=1 MHz? Note: F1 is the crystal reference oscillator frequency.

a) 1 MHz
b) 100 KHz
c) 10 KHz
d) None of the above

36. Which portion of a PLL is primarily responsible for determining the lock range?

a) VCO
b) Phase Detector
c) Low-Pass Filter
d) Reference Divider

37. When no input signal is being applied to a PLL, what state will it be in?

a) Lock
b) Capture
c) Free-Run
d) None of the above

38. Given that N=1593, R=1024, and F1 = 10.240 MHz, what will the output frequency Fout of the PLL synthesizer above be?

a) 10.240 MHz
b) 4.9152 MHz
c) 15.930 MHz
d) None of the above

39. What is the percentage modulation of an FM broadcast transmitter producing 50 KHz deviation?

a) 67%
b) 50%
c) 25%
d) None of the above

40. What is the deviation rate of an FM transmitter when the information frequency Fm = 1 KHz and the deviation is 5 KHz?

a) 1 KHz
b) 5 KHz
c) 6 KHz
d) None of the above

41. What is the total bandwidth allocated for an FM broadcast station in the USA (Including guard bands)?

a) 200 KHz
b) 150 KHz
c) 75 KHz
d) None of the above

42. What type of the transmitters convert input (information) amplitude changes into output carrier frequency changes?

a) FM
b) AM
c) PM
d) None of the above

43. What value should N have in the figure above to get an output frequency of 91.900 MHz? F1=10.000 MHz and R=100.

a) 9190
b) 5620
c) 919
d) 867
e) None of the above

44. A 7 MHz crystal oscillator is being driven so that it has 1100 Hz of deviation. This signal is fed into an X5 frequency multiplier. What is the resultant output frequency and deviation?

a) Fout=35 MHz, Deviation=5.5 KHz
b) Fout=21 MHz, Deviation=3.3 KHz
c) Fout=15 MHz, Deviation=1 KHz
d) None of the above

45. What type of FM transmitter is pictured above?

a) Armstrong WBFM
b) PLL
c) Crosby Frequency-Locked-Loop
d) None of the above

46. A 5 MHz crystal oscillator is being driven so that it has 1000 Hz of deviation. This signal is fed into an X3 frequency multiplier. What is the resultant output frequency and deviation?

a) Fout=3 MHz, Deviation=2 KHz
b) Fout=5 MHz, Deviation=3 KHz
c) Fout=15 MHz, Deviation=1 KHz
d) None of the above

47. Why is AFC generally unnecessary in modern FM receivers?

a) Tolerances of LC components have become very small
b) Synthesized local oscillators are used
c) High power amplifiers are used in the audio sections
d) None of the above

48. Why is a 10.7 MHz (rather than 455 KHz) IF used in an FM broadcast receiver?

a) More gain is required to receive FM signals
b) Using a higher frequency IF reduces noise
c) FM broadcasts use much more bandwidth than AM broadcasts
d) None of the above

49. Which FM detector uses an exclusive-OR gate (phase detector) and a single LC resonant frequency in order to detect frequency changes?

a) Quadrature
b) Foster-Seeley
c) Ratio
d) PLL
e) None of these

50. Which of these FM detectors rely on a closed loop that "follows" the instantaneous frequency changes of the incoming carrier signal?

a) Quadrature
b) Foster-Seeley
c) Ratio
d) PLL
e) None of these


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