ECT261 Practice Test III

Instructions: There are 25 questions on this test. It is written in a style very similar to the REAL exam #3. 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. 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

2. What two signals should be compared by a technician to determine whether or not a PLL is in lock?

a) The VCO output and the REFERENCE
b) The VCO output and the unfiltered output from the PHASE DETECTOR
c) The REFERENCE and the LOW-PASS FILTER output
d) None of the above

3. 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

4. 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

5. 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

6. What is the approximate (CARSON'S RULE) bandwidth of an FM transmitter with a deviation of 2 KHz and information frequency of 15 KHz?

a) 4 KHz
b) 30 KHz
c) 34 KHz
d) None of the above

7. How many significant PAIRS of sidebands will be produced by an FM transmitter that is producing 1 KHz of deviation with a 1 KHz deviation rate (information frequency)?

a) 2
b) 1
c) 3
d) 4

8. An FM transmitter is producing 45 KHz of deviation; the information signal is 5 KHz, 10 Vpk. What will happen to the deviation if the information signal is changed to 5 Vpk?

a) The deviation will become 37 KHz
b) The deviation will become 22.5 KHz
c) The deviation will become 75 KHz
d) None of the above

9. 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

10. 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 49.860 MHz?

a) 440 mV
b) 770 mV
c) 880 mV
d) None of the above

11. An FM transmitter is producing 20 KHz of deviation with 1Vpk, 10 KHz information signal. What will happen to the deviation if the information signal is changed to 2Vpk?

a) The deviation will increase to 75 KHz
b) The deviation will decrease to 10 KHz
c) The deviation will increase to 40 KHz
d) None of the above

12. 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

13. A certain FM transmitter is operating on 29.600 MHz; the unmodulated carrier power is 50 Watts. The maximum permitted deviation is 5 KHz. What power will be delivered to the antenna at 50% modulation?

a) 25 Watts
b) 75 Watts
c) 50 Watts
d) 100 Watts

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

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

15. 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

16. Ideally, an FM transmitter converts:

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

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

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

18. 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

19. What type of FM transmitter is pictured above?

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

20. What type of FM transmitter is pictured above?

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

21. Why is FM reception generally free from interference in the form of static?

a) FM Receivers are not sensitive to amplitude variations
b) FM receivers have a very high IF frequency
c) FM receivers use class C amplifiers to reject noise
d) None of the above

22. What is the name of the amplifier that operates at a constant frequency in an FM superheterodyne receiver?

a) The audio amplifier
b) The RF amplifier
c) The IF amplifier
d) None of these

23. What stage in an FM receiver rejects amplitude disturbances?

a) Detector
b) Limiter
c) Mixer
d) Preselector

24. 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

25. What is the purpose of a LIMITER in an FM receiver?

a) Rejects the image frequency
b) Converts the carrier down to the IF frequency
c) Removes amplitude variations
d) None of the above

End of FREQUENCY MAGIC test!

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