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1. 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

2. What is the purpose of the zener diode in a power supply circuit for an oscillator?

a) To regulate the DC supply of the oscillator, preventing frequency drift
b) To lower the DC supply voltage for the oscillator
c) To eliminate RF currents on the power supply rail
d) None of the above

3. Where does the modulation take place at in a high-level transmitter?

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

4. A certain high-level transmitter produces 10 Watts of carrier power. How much power must the audio amplifier produce to 100% modulate this transmitter?

a) 2 Watts
b) 4 Watts
c) 8 Watts
d) 5 Watts
e) None of the above

5. The oscillator in a certain transmitter produces +6 dBm of output. The signal is subsequently amplified in the following stages:

Buffer: +10 dB
Modulator: +6 dB
Driver: +10 dB
Final: +14 dB
Antenna Coupler: -1 dB
What is the final output power of this transmitter in Watts?

a) 8 Watts
b) 32 Watts
c) 400 mW
d) None of these

6. 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

7. What is the function of an RF bypass capacitor?

a) To couple signal from one stage to the next
b) To couple RF energy into the antenna
c) To force RF energy to go to ground
d) None of the above

8. 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

9. 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

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. In order for an oscillator to start, the loop gain must be:

a) Greater than 1
b) Greater than or equal to 1
c) Less than 1
d) None of the above

13. A certain crystal has the following characteristics: Ls=1 H, Cs=.001 pF, Rs = 150 Ohms, Cm = 5 pF. At series-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)

14. Another name for the parallel-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. 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

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

a) 490 KHz
b) 438 KHz
c) 350 KHz
d) None of the above

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

a) 2 mW
b) 4 mW
c) 8 mW
d) None of the above

18. 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

19. Using the topology shown above, what value of RL would be optimal for a power output of 10 mW if Vcc=8 V?

a) 10K Ohms
b) 50 Ohms
c) 1000 Ohms
d) 2592 Ohms
e) None of these

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

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

21. What is the image resistance RI of the network above if RL=50 Ohms, XC2=25 Ohms, XC1=30 Ohms, XL=50 Ohms?

a) 50 Ohms
b) 10 Ohms
c) 7.5 Ohms
d) 100 Ohms
e) None of the above

22. When designing a PI (or other matching network) at moderate to high power levels, what is an appropriate design measure?

a) Obtain actual component data for the inductor and capacitors to determine their ESR/Q factors
b) Design for a right-hand Q of at least 4
c) Make sure the right-hand and left-hand Q factors are within at 20% of each other
d) None of the above

23. If Vcc=12 V, Np=100T, Ns=100T, what input RMS voltage is needed to 100% modulate the stage above?

a) 8.48V
b) 12V
c) 24V
d) None of the above

24. 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

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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