ET263 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. 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

2. 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

3. 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

4. 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

5. When the REFERENCE and VCO frequencies are equal, what state is a PLL in?

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

6. 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

7. 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

8. An FM transmitter converts information voltage into...?

a) Output amplitude changes
b) Output phase changes
c) Output frequency changes
d) None of the above

9. 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

10. An FM transmitter is producing 45 KHz of devation; the information signal is 5 KHz, 10 Vpk. What is the modulation index?

a) 9.0
b) 4.5
c) 0.6
d) None of the above

11. 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

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. 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

13. 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

14. What deviation corresponds to 100% modulation for FM broadcasts in the USA?

a) 50 KHz
b) 150 KHz
c) 25 KHz
d) 75 KHz

15. What is the purpose of guard bands?

a) To reduce distortion on received signals
b) To limit the transmitting distance to line of sight
c) To prevent adjacent channel interference
d) None of the above

16. What type of FM transmitter is pictured above?

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

17. 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

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

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

19. Ideally, an FM transmitter converts:

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

20. 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

21. What is the purpose of the AFC system in an FM receiver?

a) Corrects for local oscillator frequency drift
b) Keeps the IF amplifier gains at maximum
c) Corrects the frequency of the IF amplifier tuned circuits
d) None of the above

22. 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

23. 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

24. 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

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

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

End of FREQUENCY MAGIC test!

Grade Exam!