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. 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

2. 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

3. In the PLL pictured above, the following measurements were made:

F1 = 10.000 MHz
"A" = 100 KHz (5 Vpp square wave)
"B" = 90 KHz (5 Vpp square wave)
VCO Control Voltage = 7.9 V (Steady DC); Vcc = 8.0 V
"D" = 118.536 MHz (Unstable; this is an average).

It is known that R = 100 and N = 1001 from the service documentation. What is the most likely fault in the loop?

a) The N divider is defective (Not triggering correctly on VCO signal)
b) The R divider is defective (Not producing correct frequency at TP "A")
c) The VCO is defective (Not oscillating)
d) The phase detector is defective (Not comparing "A" and "B")
e) The loop is operating correctly

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. What is the maximum deviation permitted for FM broadcasts in the USA?

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

11. How many significant PAIRS of sidebands will be produced by an FM transmitter that is producing 1 KHz of deviation with a 5 KHz deviation rate (information frequency)?

a) 2
b) 1
c) 4
d) None of the above

12. How many significant PAIRS of sidebands will be produced by an FM transmitter that is producing 2 KHz of deviation with a 1 KHz deviation rate (information frequency)?

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

13. A certain FM transmitter operates on 95.3 MHz. The maximum frequency from the transmitter is 95.325 MHz, and the minimum frequency is 95.275 MHz. What is the percentage of modulation?

a) 67%
b) 100%
c) 25%
d) 33%

14. 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

15. 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

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. Ideally, an FM transmitter converts:

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

19. If the frequency at TP "A" in the figure above is 95.300 MHz, what is the MOST LIKELY frequency at TP "D"?

a) 95.300 MHz
b) 93.300 MHz
c) 91.900 MHz
d) None of the above

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

a) A
b) B
c) C
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. An FM detector can be ideally viewed as a/an:

a) Frequency to voltage converter
b) Voltage to frequency converter
c) Amplitude to current converter
d) None of the above

23. 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

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

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

25. 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

End of FREQUENCY MAGIC test!

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