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1. 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

2. 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

3. 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

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. What is the function of a VCO?

a) Converts voltage to frequency
b) Converts frequency to voltage
c) Converts voltage to phase
d) None of the above

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

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

7. 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

8. 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

9. 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

10. 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

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

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

12. 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

13. 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

14. 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

15. 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 deviation?

a) 50 KHz
b) 150 KHz
c) 25 KHz
d) None of the above

16. 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

17. 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

18. 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

19. 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

20. Ideally, an FM transmitter converts:

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

21. 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

22. 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

23. 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

24. 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

25. 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

End of FREQUENCY MAGIC test!

Grade Exam!