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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 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

3. 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

4. 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

5. 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

6. 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

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

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

8. 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

9. 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

10. 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

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. 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

13. 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

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

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

17. Ideally, an FM transmitter converts:

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

18. 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

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. What type of FM transmitter is pictured above?

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

21. 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

22. 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

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. 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

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!