This is the Multiple Choice Questions in Chapter 5: Transmitters from the book Electronic Communication Systems by Roy Blake
Start Practice Exam Test Questions
Choose the letter of the best answer in each questions.
MULTIPLE CHOICE
1. The ability to change operating frequency rapidly without a lot of retuning is called:
- a. agility
- b. expansion
- c. VFO
- d. spread-spectrum
ANS: A
2. The difference between the DC power into a transmitter and the RF power coming out:
- a. is a measure of efficiency
- b. heats the transmitter
- c. may require water cooling
- d. all of the above
ANS: D
3. Baseband compression produces:
- a. a smaller range of frequencies from low to high
- b. a smaller range of amplitude from soft to loud
- c. a smaller number of signals
- d. none of the above
ANS: B
4. ALC stands for:
- a. Amplitude Level Control
- b. Automatic Level Control
- c. Accurate Level Control
- d. none of the above
ANS: B
5. In an AM transmitter, ALC is used to:
- a. keep the modulation close to 100%
- b. keep the modulation below 100%
- c. maximize transmitted power
- d. all of the above
ANS: D
6. With high-level AM:
- a. all RF amplifiers can be nonlinear
- b. minimum modulation power is required
- c. minimum RF power is required
- d. all of the above
ANS: A
7. With high-level AM:
- a. the RF amplifiers are typically Class A
- b. the RF amplifiers are typically Class B
- c. the RF amplifiers are typically Class C
- d. the RF amplifiers are typically Class AB
ANS: C
8. With low-level AM:
- a. the RF amplifiers must be Class A
- b. the RF amplifiers must be Class B
- c. the RF amplifiers must be linear
- d. the RF amplifiers must be low-power
ANS: C
9. Power amplifiers must be linear for any signal that:
- a. is complex
- b. has variable amplitude
- c. has variable frequency
- d. all of the above
ANS: B
10. In high-level AM, "high-level" refers to:
- a. the power level of the carrier
- b. the power level of the modulation
- c. the power level of the final RF amplifier
- d. none of the above
ANS: D
11. In high-level AM, the power in the sidebands comes from:
- a. the modulating amplifier
- b. the RF amplifier
- c. the driver stage
- d. the carrier
ANS: A
12. In an AM transmitter with 100% modulation, the voltage of the final RF stage will be:
- a. approximately half the DC supply voltage
- b. approximately twice the DC supply voltage
- c. approximately four times the DC supply voltage
- d. none of the above
ANS: C
13. Practical transmitters are usually designed to drive a load impedance of:
- a. 50 ohms resistive
- b. 75 ohms resistive
- c. 300 ohms resistive
- d. 600 ohms resistive
ANS: A
14. Which of the following can be used for impedance matching?
- a. pi network
- b. T network
- c. both a and b
- d. a bridge circuit
ANS: C
15. When a transmitter is connected to a resistor instead of an antenna, the resistor is called:
- a. a heavy load
- b. a dummy load
- c. a temporary load
- d. a test load
ANS: B
16. When a transmitter is connected to a resistor instead of an antenna, the resistor must be:
- a. wire-wound
- b. noninductive
- c. 1% tolerance or better
- d. all of the above
ANS: B
17. A Class D amplifier is:
- a. very efficient
- b. essentially pulse-width modulation
- c. essentially pulse-duration modulation
- d. all of the above
ANS: D
18. To generate a SSB signal:
- a. start with full-carrier AM
- b. start with DSBSC
- c. start with a quadrature signal
- d. all of the above
ANS: B
19. The carrier is suppressed in:
- a. a balanced modulator
- b. a mixer
- c. a frequency multiplier
- d. none of the above
ANS: A
20. To remove one AM sideband and leave the other you could use:
- a. a mechanical filter
- b. a crystal filter
- c. both a and b
- d. none of the above
ANS: C
21. A direct FM modulator:
- a. varies the frequency of the carrier oscillator
- b. integrates the modulating signal
- c. both a and b
- d. none of the above
ANS: A
22. An indirect FM modulator:
- a. requires a varactor in the carrier oscillator
- b. varies the phase of the carrier oscillator
- c. both a and b
- d. none of the above
ANS: B
23. AFC stands for:
- a. Amplitude to Frequency Conversion
- b. Automatic Frequency Centering
- c. Automatic Frequency Control
- d. Audio Frequency Control
ANS: C
24. Frequency multipliers are:
- a. essentially balanced modulators
- b. essentially Class C amplifiers
- c. essentially mixers
- d. none of the above
ANS: B
25. With mixing:
- a. the carrier frequency can be raised
- b. the carrier frequency can be lowered
- c. the carrier frequency can be changed to any required value
- d. the deviation is altered
ANS: C
COMPLETION
1. The accuracy and stability of a transmitter frequency is fixed by the ____________________ oscillator.
ANS: carrier
2. In the USA, the ____________________ sets requirements for accuracy and stability of a transmitter's frequency.
ANS: FCC
3. In Canada, _________________________ sets requirements for accuracy and stability of a transmitter's frequency.
ANS: Industry Canada
4. Frequency ____________________ is the ability of a transmitter to change frequency without a lot of retuning.
ANS: agility
5. Power output of SSB transmitters is rated by ____________________.
ANS: PEP
6. Reducing the dynamic range of a modulating signal is called ____________________.
ANS: compression
7. The opposite of compression is called ____________________.
ANS: expansion
8. ALC is a form of ____________________.
ANS: compression
9. High-level modulation allows the RF amplifiers to operate more ____________________.
ANS: efficiently
10. Low-level modulation requires the RF amplifiers to be ____________________.
ANS: linear
11. To isolate the oscillator from load changes, a ____________________ stage is used.ANS: buffer
12. The peak collector voltage in a Class C RF amplifier is ____________________ than the DC supply voltage.
ANS: higher
13. Most practical transmitters are designed to operate into a ____________________-ohm load.
ANS: 50
14. Transmitters built with transistor RF amplifiers often use a ____________________ network for impedance matching.
ANS: T
15. Matching networks also act as filters to help reduce ____________________ levels.
ANS: harmonic
16. Severe impedance ____________________ can destroy a transmitter's output stage.
ANS: mismatch
17. Transceivers combine a transmitter and a ____________________ into one "box".
ANS: receiver
18. To allow a high modulation percentage, it is common to modulate the ____________________ as well as the power amplifier in transistor modulators.
ANS: driver
19. Pulse-width modulation is the same as pulse-____________________ modulation.
ANS: duration
20. Switching amplifiers are sometimes called Class ____________________ amplifiers.
ANS: D
21. Because the sideband filter in a SSB transmitter is fixed, ____________________ is used to operate at more than one frequency.
ANS: mixing
22. To generate a SSB signal, it is common to start with a ____________________ signal.
ANS: DSBSC23. Indirect FM is derived from ____________________ modulation.
ANS: phase
24. Using a varactor to generate FM is an example of a ____________________ modulator.
ANS: reactance
25. The modern way to make a stable VFO is to make it part of a ____________________ loop.
ANS: phase-locked
SHORT ANSWER
1. If a 50-MHz oscillator is accurate to within 0.001%, what is the range of possible frequencies?
ANS:
50 MHz – 500 hertz
2. What is the efficiency of a 100-watt mobile transmitter if it draws 11 amps from a 12-volt car battery?
ANS:
75.8%
3. The power amplifier of an AM transmitter draws 100 watts from the power supply with no modulation. Assuming high-level modulation, how much power does the modulation amplifier deliver for 100% modulation?
ANS:
50 watts
4. If the final RF amplifier of an AM transmitter is powered by 100 volts DC, what is the maximum collector voltage at 100% modulation?
ANS:
400 volts
5. Suppose the output of a balanced modulator has a center frequency of 10 MHz. The audio modulation frequency range is 1 kHz to 10 kHz. To pass the USB, what should be the center frequency of an ideal crystal filter?
ANS:
10.005 MHz
6. Suppose you have generated a USB SSB signal with a nominal carrier frequency of 10 MHz. What is the minimum frequency the SSB signal can be mixed with so that the output signal has a nominal carrier frequency of 50 MHz?
ANS:
40 MHz
7. Suppose you have an FM modulator that puts out 1 MHz carrier with a 100-hertz deviation. If frequency multiplication is used to increase the deviation to 400 hertz, what will be the new carrier frequency?
ANS:
4 MHz
8. Suppose you had an FM signal with a carrier of 10 MHz and a deviation of 10 kHz. Explain how you could use it to get an FM signal at 100 MHz with a deviation of 20 kHz.
ANS:
First, put the signal through a frequency doubler to get a 20-MHz carrier with a 20-kHz deviation. Then mix that signal with an 80-MHz carrier to generate a 100-MHz carrier with 20-kHz deviation.
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