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. 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

2. Where would one expect to find an RF bypass capacitor connected within a radio transmitter?

a) Between the final PA stage and the antenna
b) Between the oscillator and buffer amplifier
c) Between a power supply line and ground
d) None of the above

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

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. 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

12. What is the operating frequency of the oscillator pictured above?

a) 599.412 KHz
b) 847.697 KHz
c) 455.000 KHz
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. 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 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 parallel-resonant frequency of the unit?

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

16. 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

17. 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

18. 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

19. 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

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. 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. If Vcc=10 V, what voltage can be expected at test point A in a properly-operating unit?

a) 20Vp-p
b) 10Vp-p
c) 5Vp-p
d) None of the above

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