# Blake: MCQ in Radio-Frequency Circuits

(Last Updated On: January 10, 2018)

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

ANS: B

2. A real capacitor actually contains:

• a. capacitance and resistance only
• b. capacitance and inductance only
• c. capacitance, inductance, and resistance
• d. reactance only

ANS: C

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

ANS: A

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

ANS: C

5. Loading down a tuned-circuit amplifier will:

• 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

ANS: B

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

ANS: D

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

ANS: B

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

• a. inductance of collector lead
• b. collector-to-emitter capacitance d
• c. base-to-emitter capacitance
• d. base-to-collector capacitance

ANS: D

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

• a. RC coupling
• b. transformer coupling
• c. direct coupling
• d. lumped reactance

ANS: B

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

ANS: A

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

ANS: A

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

ANS: C

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

ANS: D

14. The Hartley oscillator uses:

• a. a tapped inductor
• b. a two-capacitor divider
• c. an RC time constant
• d. a piezoelectric crystal

ANS: A

15. The Colpitts VFO uses:

• a. a tapped inductor
• b. a two-capacitor divider
• c. an RC time constant
• d. a piezoelectric crystal

ANS: B

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

ANS: B

17. A varactor is:

• a. a voltage-controlled capacitor
• b. a diode
• c. used in tuner circuits
• d. all of the above

ANS: D

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

ANS: D

19. If two signals, Va = sin(ωat) and Vb = sin(ωbt), are fed to a mixer, the output:

• a. will contain ω1 = ωa + ωb and ω2 = ωa – ωb
• b. will contain ω1 = ωa / ωb and ω2 = ωb / ωa
• c. will contain ω1 = (ωa + ωb ) / 2
• d. none of the above

ANS: A

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

ANS: C

21. "VFO" stands for:

• a. Voltage-Fed Oscillator
• b. Variable-Frequency Oscillator
• c. Varactor-Frequency Oscillator
• d. Voltage-Feedback Oscillator

ANS: B

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

ANS: A

COMPLETION

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

ANS: short

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

ANS: distributed

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

ANS: ground-plane

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

ANS: shielding

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

ANS: components

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

ANS: decoupling

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

ANS: bypass

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

ANS: Q

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

ANS: 10

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

ANS: tuned circuit

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

ANS: neutralization

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

ANS: capacitive

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

ANS: series, parallel

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

ANS: linear

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

ANS: square

SHORT ANSWER

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

ANS:

5.4 µH

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

ANS:

100

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?

ANS:

0.1

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

ANS:

It is more stable because it "swamps" the device capacitance with large value capacitors in the feedback divider.

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

ANS:

30 pF

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

ANS:

50 kHz, 0.05%

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?

ANS:

15 MHz and 25 MHz

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?

ANS:

12

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

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