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# Blake: MCQ in Radio-Frequency Circuits

This is the Multiple Choice Questions in Chapter 2: Radio-Frequency Circuits from the book Electronic Communication Systems by Roy Blake. If you are looking for a reviewer in Communications Engineering this will definitely help. I can assure you that this will be a great help in reviewing the book in preparation for your Board Exam. Make sure to familiarize each and every questions to increase the chance of passing the ECE Board Exam.

#### Start Practice Exam Test Questions

Choose the letter of the best answer in each questions.

MULTIPLE CHOICE

1. The time it takes a charge carrier to cross from the emitter to the collector is called:

a. base time

b. transit time

c. charge time

d. Miller time

Solution:

2. A real capacitor actually contains:

a. capacitance and resistance only

b. capacitance and inductance only

c. capacitance, inductance, and resistance

d. reactance only

Solution:

3. Bypass capacitors are used to:

a. remove RF from non-RF circuits

b. couple RF around an amplifier

c. neutralize amplifiers

d. reduce the Miller effect

Solution:

4. A resonant circuit is:

a. a simple form of bandpass filter

b. used in narrowband RF amplifiers

c. both a and b

d. none of the above

Solution:

a. raise the Q of the tuned circuit

b. lower the Q of the tuned circuit

c. “multiply” the Q

d. have no effect on Q

Solution:

6. The “Miller Effect” can:

a. cause an amplifier to oscillate

b. cause an amplifier to lose gain

c. reduce the bandwidth of an amplifier

d. all of the above

Solution:

7. The Miller Effect can be avoided by:

a. using a common-emitter amplifier

b. using a common-base amplifier

c. increasing the Q of the tuned circuit

d. it cannot be avoided

Solution:

8. In a BJT, the Miller Effect is due to:

b. collector-to-emitter capacitance d

c. base-to-emitter capacitance

d. base-to-collector capacitance

Solution:

9. In RF amplifiers, impedance matching is usually done with:

a. RC coupling

b. transformer coupling

c. direct coupling

d. lumped reactance

Solution:

10. Neutralization cancels unwanted feedback by:

a. adding feedback out of phase with the unwanted feedback

b. bypassing the feedback to the “neutral” or ground plane

c. decoupling it

d. none of the above

Solution:

11. For a “frequency multiplier” to work, it requires:

a. a nonlinear circuit

b. a linear amplifier

c. a signal containing harmonics

d. an input signal that is an integer multiple of the desired frequency

Solution:

12. A sinusoidal oscillation from an amplifier requires:

a. loop gain equal to unity

b. phase shift around loop equal to 0 degrees

c. both a and b, but at just one frequency

d. none of the above

Solution:

13. The conditions for sinusoidal oscillation from an amplifier are called:

a. the loop-gain criteria

b. the Hartley criteria

c. the Bode criteria

d. the Barkhausen criteria

Solution:

14. The Hartley oscillator uses:

a. a tapped inductor

b. a two-capacitor divider

c. an RC time constant

d. a piezoelectric crystal

Solution:

15. The Colpitts VFO uses:

a. a tapped inductor

b. a two-capacitor divider

c. an RC time constant

d. a piezoelectric crystal

Solution:

16. The Clapp oscillator is:

a. a modified Hartley oscillator

b. a modified Colpitts oscillator

c. a type of crystal-controlled oscillator

d. only built with FETs

Solution:

17. A varactor is:

a. a voltage-controlled capacitor

b. a diode

c. used in tuner circuits

d. all of the above

Solution:

18. Crystal-Controlled oscillators are:

a. used for a precise frequency

b. used for very low frequency drift (parts per million)

c. made by grinding quartz to exact dimensions

d. all of the above

Solution:

19. If two signals, Va = sin(ฯat) and Vb = sin(ฯbt), are fed to a mixer, the output:

a. will contain ฯ1 = ฯa + ฯb and ฯ2 = ฯa โ ฯb

b. will contain ฯ1 = ฯa / ฯb and ฯ2 = ฯb / ฯa

c. will contain ฯ1 = (ฯa + ฯb ) / 2

d. none of the above

Solution:

20. In a balanced mixer, the output:

a. contains equal (balanced) amounts of all input frequencies

b. contains the input frequencies

c. does not contain the input frequencies

d. is a linear mixture of the input signals

Solution:

21. “VFO” stands for:

a. Voltage-Fed Oscillator

b. Variable-Frequency Oscillator

c. Varactor-Frequency Oscillator

d. Voltage-Feedback Oscillator

Solution:

22. A “frequency synthesizer” is:

a. a VCO phase-locked to a reference frequency

b. a VFO with selectable crystals to change frequency

c. a fixed-frequency RF generator

d. same as a mixer

Solution:

COMPLETION

1. Generally, conductor lengths in RF circuits should be ____________________.

Solution:

2. At UHF frequencies and above, elements must be considered as ____________________ instead of as being “lumped”.

Solution:

3. When one side of a double-sided pc board is used for ground, it is called a ____________________.

Solution:

4. Interactions between parts of an RF circuit can be reduced by using ____________________ between them.

Solution:

5. In high-frequency RF circuits, the placement of wires and ____________________ can be critical.

Solution:

6. A ____________________ circuit is used to remove RF from the DC voltage bus.

Solution:

7. A ____________________ capacitor is used to short unwanted RF to ground.

Solution:

8. The bandwidth of a tuned-circuit amplifier depends on the ____________________ of the tuned circuit.

Solution:

9. A value of ____________________ or more for Q is required for the approximate tuned circuit equations to be valid.

Solution:

10. In a class C RF amplifier, the ____________________ extracts one frequency from all the harmonics contained in the device current (e.g. collector current).

Solution:

11. Using additional feedback to compensate for “stray” feedback is called ____________________.

Solution:

12. A Colpitts oscillator uses a ____________________ voltage divider to provide feedback.

Solution:

13. Electrically, a piezoelectric crystal has both a ____________________ and a ____________________ resonant frequency.

Solution:

14. To produce sum and difference frequencies, a mixer must be a non-____________________ circuit.

Solution:

15. At some bias point, a diode or a transistor can act as a ____________________-law mixer.

Solution:

1. What inductance would you use with a 47-pF capacitor to make a tuned circuit for 10 MHz?

Solution:

2. What value of Q is required for a 10-MHz tuned circuit to have a bandwidth of 100 kHz?

Solution:

3. A tuned-circuit amplifier with a gain of 10 is being used to make an oscillator. What should be the value of the feedback ratio to satisfy the Barkhausen criteria?

Solution:

4. What is the advantage of a Clapp oscillator compared to a Colpitts oscillator?

Answer: It is more stable because it “swamps” the device capacitance with large value capacitors in the feedback divider.

Solution:

5. If a varactor has a capacitance of 90 pF at zero volts, what will be the capacitance at 4 volts?

Solution:

6. An oscillator has a frequency of 100 MHz at 20ยฐC, and a tempco of +10 ppm per degree Celsius. What will be the shift in frequency at 70ยฐC? What percentage is that?

Solution:

7. Two sinusoidal signals, V1 and V2, are fed into an ideal balanced mixer. V1 is a 20-MHz signal; V2 is a 5- MHz signal. What frequencies would you expect at the output of the mixer?

Answer: 15 MHz and 25 MHz

Solution:

8. Suppose the phase-locked-loop frequency synthesizer of Figure 2.39 has a reference frequency of 1 MHz and a fixed-modulus divider of 10. What should be the value of the programmable divider to get an output frequency of 120 MHz?

Solution:

#### Complete List of MCQ in Electronic Communication Systems by Blake

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