ECT261 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.

Note: You can practice this test as many times as you desire; the system will cook you up a fresh batch of questions each time you access this page.

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1. 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

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. 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

4. 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

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. 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

7. 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

8. 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

9. What type of oscillator is pictured above?

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

10. 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

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. Another name for the parallel-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. 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

15. 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)

16. 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

17. The purpose of the frequency converter section of a superhet receiver is to:

a) Keep the output level at the speaker constant, regardless of input signal level changes
b) Eliminate the image response
c) Prevent local oscillator frequency drift
d) None of these

18. The DC component from the AM detector is used for what purpose?

a) To reduce distortion in the audio amplifier
b) To prevent frequency drift in the local oscillator
c) To control the gain of the RF and IF stages (AGC)
d) None of the above

19. Which section of a superhet receiver determines the receiver's bandwidth?

a) Detector
b) Preselector
c) IF Amplifier
d) None of these

20. What section of a superheterodyne receiver determines the receiver's bandwidth and selectivity?

a) Preselector
b) IF Amplifier
c) Detector
d) Audio Amplifier
e) None of the above

21. What is the name of the amplifier that operates at a constant frequency in a superhet receiver?

a) The audio amplifier
b) The RF amplifier
c) The IF amplifier
d) None of these

22. The two signal components that are produced in a diode-type AM detector circuit are:

a) The upper and lower sidebands
b) A DC level and the AC information signal
c) The carrier frequency and sidebands
d) None of these

23. How is a mixer forced to be nonlinear?

a) One frequency applied is higher than the other
b) It is driven into large-signal mode by one of the signal sources
c) The power supply to the mixer is made as large as possible
d) None of these

24. What is the function of the preselector in a superhet receiver?

a) Boosts the gain of the IF amplifier
b) Used to produce the AGC control signal
c) Eliminates the image frequency
d) None of these

25. What is meant by the term "high-side injection?"

a) The local oscillator operates with a large AC output signal
b) The IF amplifier uses negative-bias to produce AGC
c) The local oscillator operates above the frequency of the RF carrier
d) None of the above

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