ET263 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. Why can't audio frequencies be directly transmitted through an antenna system?

a) The antenna required would be too long
b) Too much power would be required
c) The receiver would distort the information waveform
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 are the steps of troubleshooting in correct order?

a) Visual inspection, Check power supply, Check inputs & outputs
b) Check power supply, Visual inspection, Check inputs & outputs
c) Visual inspection, Check inputs & outputs, Check power supply
d) None of the above

4. What frequency is two octaves above 1 KHz?

a) 2 KHz
b) 3 KHz
c) 5 KHz
d) None of the above

5. What is the frequency of the 3rd harmonic for the signal above?

a) 1 KHz
b) 2 KHz
c) 3 KHz
d) None of these

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

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

7. What type of noise is produced by devices with forward-biased PN junctions?

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

8. Which of these measures would decrease shot noise?

a) Decrease the forward DC bias current
b) Increase the junction voltage drop
c) Increase the forward DC bias current
d) None of the above

9. To double the power of a Johnson noise source, what would be done?

a) Double the current
b) Double the bandwidth
c) Halve the resistance
d) None of the above

10. What is the total bandwidth of the AM signal pictured above?

a) 500 Hz
b) 1 KHz
c) 2 KHz
d) 4 KHz

11. What is the percentage of modulation for the AM signal above?

a) 50%
b) 60%
c) 70.7%
d) None of the above

12. An AM signal was measured on an oscilloscope. The readings were Vmax=400 V, and Vmin = 100V. What is the percent modulation?

a) 33.3%
b) 60 %
c) 75 %
d) None of the above

13. An AM signal was measured on an oscilloscope. The readings were Vmax=300 V, and Vmin = 150V. What is the percent modulation?

a) 33.3 %
b) 50 %
c) 75 %
d) None of the above

14. Which of these is a consequence of overmodulating an AM transmitter?

a) Distortion of the information
b) Splatter (Excessive bandwidth)
c) Both A and B
d) None of the above

15. 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

16. Which of these is an important property for a modulator stage to have?

a) High voltage gain
b) High power gain
c) Low input-impedance
d) Non-linear transfer characteristic

17. What is the function of an RF bypass capacitor?

a) To couple signal from one stage to the next
b) To couple RF energy into the antenna
c) To force RF energy to go to ground
d) None of the above

18. What class of amplifier would be serve as a modulator?

a) Class A
b) Class B
c) Class C
d) None of the above

19. Where would one expect to find an RF bypass capacitor connected within a radio transmitter?

a) Between the final PA stage and the antenna
b) Between the oscillator and buffer amplifier
c) Between a power supply line and ground
d) None of the above

20. 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

21. What type of oscillator is pictured above?

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

22. 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

23. 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

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

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

27. 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

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 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

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. A superhet receiver is using high-side injection. The incoming RF signal has a carrier frequency of 560 KHz; the IF frequency is 455 KHz. What is the image frequency?

a) 1470 KHz
b) 1015 KHz
c) 1120 KHz
d) 1165 KHz
e) None of these

32. 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

33. What section of a superheterodyne receiver determines the receiver's bandwidth and selectivity?

a) Preselector
b) IF Amplifier
c) Detector
d) Audio Amplifier
e) None of the above

34. What is the first step that must take place in receiving a radio signal?

a) Select (Tune desired carrier frequency)
b) Demodulate (Detect)
c) Amplify RF Signal
d) Acquire an RF signal

35. Given that N=2442, R=10240, and F1 = 10.240 MHz, what will the output frequency Fout of the PLL synthesizer above be?

a) 1.024 MHz
b) 20.480 MHz
c) 8.192 MHz
d) 2.442 MHz

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

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

37. How can a technician determine that a PLL is in lock?

a) Check that Vcontrol = Vcc/2
b) Check that Fvco = Fref
c) Check that Fvco = Fref / 2
d) None of the above

38. Which part of a PLL converts voltage changes into frequency changes?

a) Phase Detector
b) Low Pass Filter
c) VCO
d) None of the above

39. An FM transmitter is operating on 49.860 MHz. Fm = 5 KHz and the deviation is 5 KHz. The unmodulated carrier voltage is 1V. The information voltage is 3Vpk. What MINIMUM information voltage will cause the 49.860 frequency component (as viewed on a spectrum analyzer) to become ZERO?

a) 3.24 Vpk
b) 5.00 Vpk
c) 7.20 Vpk
d) None of the above

40. What is the approximate (CARSON'S RULE) bandwidth of an FM transmitter with a deviation of 5 KHz and information frequency of 1 KHz?

a) 10 KHz
b) 2 KHz
c) 15 KHz
d) None of the above

41. An FM transmitter is operating on 49.860 MHz. Fm = 5 KHz and the deviation is 5 KHz. The unmodulated carrier voltage is 1V. If the output of this transmitter is viewed on a spectrum analyzer, what voltage will be visible at the frequency 49.865 MHz?

a) 440 mV
b) 1000 mV
c) 880 mV
d) None of the above

42. A NARROWBAND FM (NBFM) signal has how many pairs of significant sidebands?

a) 1
b) 2
c) 3
d) 4
e) None of these

43. Which class of amplifier is generally preferred for power amplification in FM transmitters?

a) A
b) B
c) C
d) None of the above

44. What type of FM transmitter is pictured above?

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

45. Ideally, an FM transmitter converts:

a) Voltage to Frequency
b) Voltage to Current
c) Frequency to Voltage
d) None of the above

46. Why is it possible to amplify FM signals in a class C amplifier?

a) The maximum power is no more than twice the unmodulated power
b) The power in an FM signal is constant
c) The bandwidth of FM signals quite small, less than 10 KHz
d) None of the above

47. 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

48. Where is the demodulated signal taken out of a PLL FM demodulator?

a) At the reference oscillator
b) At the VCO output
c) At the loop filter output
d) None of these

49. 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

50. What would be used for deemphasis in an FM receiver?

a) An LC bandpass filter
b) An RC highpass filter
c) An RC lowpass filter
d) None of the above


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