EET368 Practice Test II

Instructions: There are 25 questions on this test. It is written in a style very similar to the REAL exam #2. Choose the best answer from among those given. Click the GRADE button on the bottom of the form when you want the exam graded.

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1. 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

2. 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

3. 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

4. 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

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

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

6. 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

7. What is meant by the term "dead-keyed?"

a) The unmodulated condition; 0% modulation
b) 50% modulated
c) 100% modulated; maximum output power
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. What type of oscillator is pictured above?

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

10. 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

11. A certain oscillator has an amplifier with a phase shift of 45 degrees. According to the Barkhausen criteria for oscillation, what phase shift in the FEEDBACK network would be necessary to cause oscillation?

a) 90 Degrees
b) -45 Degrees
c) 315 Degrees
d) (b) or (c)
e) None of the above

12. What type of oscillator is pictured above?

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

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

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

14. 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)

15. Another name for the parallel-resonant frequency of a crystal is the:

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

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. 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

18. What is the bandwidth of the amplifier above?

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

19. Using the topology shown above, what value should be used for L1 if a center frequency of 200 KHz with a bandwidth of 10 KHz is desired? The load resistance is 5K Ohms.

a) 198 uH
b) 1 mH
c) 10 nH
d) 465 nH
e) None of these

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

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

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. 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 R'L is 10 Ohms and Vcc=12 V, what CW power output will be produced by the unit pictured above?

a) 10 W
b) 7.2 W
c) 25 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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