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1. Why would the power supply to an oscillator stage be regulated?

a) To provide maximum power output from the oscillator
b) To prevent the oscillator from producing a distorted sine wave
c) To prevent the oscillator from being "pulled" off frequency
d) None of the above

2. Why would a class C amplifier be an excellent choice for use as a modulator in a radio transmitter?

a) The class C amplifier generates very low levels of distortion
b) The class C amplifier can operate on very low supply voltages
c) The class C amplifier is very nonlinear -- a requirement for modulation
d) None of the above

3. The oscillator in a certain transmitter produces 1 mW of output. The signal is subsequently amplified in the following stages:

Buffer: +10 dB
Modulator: +6 dB
Driver: +10 dB
Final: +13 dB

What is the final output power of this transmitter in Watts?

a) 8 Watts
b) 4 Watts
c) 400 mW
d) None of these

4. Where does the modulation take place at in a low-level transmitter?

a) At the oscillator
b) At the final power amplifier
c) At the buffer amplifier
d) Before the final power amplifier

5. To isolate a transmitter's carrier oscillator from undesired load changes, what stage is often used?

a) A buffer amplifier
b) A class C amplifier
c) A power amplifier
d) None of the above

6. What class of amplifier would be serve as a modulator?

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

7. What is the purpose of a buffer amplifier?

a) To provide a large voltage gain
b) To isolate the oscillator from the next stage
c) To reduce distortion of the carrier sine wave
d) None of the above

8. Which of these is an important property for a modulator stage to have?

a) High voltage gain
b) High power gain
c) Low input-impedance
d) Non-linear transfer characteristic

9. What type of oscillator is pictured above?

a) Colpitts
b) Hartley
c) Armstrong
d) Pierce
e) None of the above

10. What type of oscillator is pictured above?

a) Colpitts
b) Hartley
c) Armstrong
d) Pierce
e) None of the above

11. What type of oscillator is pictured above?

a) Colpitts
b) Hartley
c) Armstrong
d) Pierce
e) None of the above

12. Which of these devices would provide the most stable oscillation frequency?

a) An RC time-constant
b) An LC resonant circuit
c) A quartz crystal
d) A ceramic resonator

13. A certain crystal has the following characteristics: Ls=1 H, Cs=.001 pF, Rs = 150 Ohms, Cm = 5 pF. What is the series-resonant frequency of the unit?

a) 5.032921 MHz
b) 4.986123 MHz
c) 5.033424 MHz
d) None of the above

14. Another name for the series-resonant frequency of a crystal is the:

a) Pole
b) Zero
c) Maximum
d) Minimum

15. A certain crystal has the following characteristics: Ls=1 H, Cs=.001 pF, Rs = 150 Ohms, Cm = 5 pF. At parallel-resonance, what is the approximate terminal impedance of the unit?

a) 30 + j125 Ohms
b) 30 - j150 Ohms
c) 150 Ohms (Equal to Rs)
d) Infinity (Open Circuit)

16. What is the center frequency of the amplifier above?

a) 262 KHz
b) 411 KHz
c) 900 KHz
d) None of the above

17. What load resistance is seen by the transistor collector in the amplifier above?

a) 50 Ohms
b) 500 Ohms
c) 5K Ohms
d) None of the above

18. What power output is available from the amplifier above?

a) 6.6 mW
b) 10 mW
c) 5 mW
d) None of the above

19. What is the bandwidth of the amplifier above?

a) 50 KHz
b) 100 KHz
c) 10.6 KHz
d) None of the above

20. Using the topology shown above, what value should be used for L1 if a center frequency of 400 KHz with a bandwidth of 10 KHz is desired? The load resistance is 10K Ohms.

a) 198 uH
b) 99.4 uH
c) 22 nH
d) 470 nH
e) None of these

21. Where would the network above most likely be found in a transmitter?

a) At the oscillator stage
b) At the modulator stage
c) Between the final PA and antenna
d) None of the above

22. What is the input impedance of the pi-network shown above if RL=50 Ohms, XL=50 Ohms, XC1=50 Ohms, and XC2=50 Ohms?

a) 50 Ohms
b) 25+3j Ohms
c) 75 Ohms
d) 100 Ohms
e) None of the above

23. If Vcc=12V and R'L is 5 Ohms in the figure above, what audio input power will be needed to obtain 100% modulation?

a) 14.4 W
b) 28.8 W
c) 7.2 W
d) None of the above

24. If Vcc=14 V, Np=50T, Ns=100T, what input peak voltage is needed to 100% modulate the stage above?

a) 14Vpk
b) 7Vpk
c) 21Vpk
d) None of the above

25. What percentage modulation will be obtained in the figure above if the audio input signal is 5 Vpk, Vcc=20V, Np=50T, Ns=100T, and R'L = 7 Ohms?

a) 25%
b) 50%
c) 75%
d) 100%
e) None of the above

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