Deck 3: Amplitude Modulation: Reception

Question 1

Varactor diodes are used for tuning by:

A) capacitance adjustment through forward bias.
B) capacitance adjustment through a reverse bias diode.
C) temperature compensation of diodes.
D) all of the above

Answer 1

B

Question 2

The diode detector:

A) one of the simplest and most effective AM detectors
B) is sometimes referred to as an envelope detector
C) consists of a nonlinear diode and low-pass filter
D) all of the above

Answer 2

D

Question 3

In a varactor diode, as voltage increases, capacitance:

A) decreases
B) increases
C) stays the same
D) none of the above

Answer 3

A

Question 4

Image frequency rejection on a standard AM broadcast band receiver is not a major problem since:

A) the image frequency is not close to the IF frequency
B) the image frequency is so far away from the RF amplifier stage's tuned frequency
C) the image frequency is not produced by mixing action
D) the image frequency is not close to the LO frequency

Question 5

Which of the following is not an advantage of a synchronous detection?

A) Low distortion
B) Ability to produce gain
C) Eliminate diagonal clipping
D) ability to follow fast-modulated signals

Question 6

A receiver's selectivity is:

A) the ability of a receiver to attenuate noise signals.
B) the extent to which a receiver is capable of differentiating between the desired signal and other signals.
C) its ability to drive the output speaker to an acceptable level.
D) the ability of the receiver to demodulate a modulated signal.

Question 7

The only roadblock to having complete receivers on a chip aside from station selection and volume controls is:

A) IF amplifier.
B) limiting factors of tuned circuits.
C) local oscillator.
D) mixer circuits.

Question 8

Which is not an advantage of diode detectors?

A) They are highly efficient.
B) They develop a readily usable dc voltage for automatic gain control circuits.
C) Power absorbed from the tuned circuit by the diode detector reduces the Q of the tuned circuit.
D) Distortion decreases as the amplitude of the AM signal increases.

Question 9

A TRF receiver is to be designed with a single tuned circuit using an 8.2 uH inductor. If the frequency is to be tuned from 55 kHz to 1600 kHz, find the BW that results at 550 kHz if there is exactly 10 kHz BW at a frequency of 1050 kHz

A) 10 kHz
B) 15.24 kHz
C) 105 kHz
D) 5.24 kHz

Question 10

The mixer is often referred to as:

A) an RF amplifier.
B) a first detector.
C) an oscillator generator.
D) a second detector.

Question 11

If a receiver is underselective:

A) more than one radio station on different frequencies may be picked up by the receiver at the same time
B) only part of the bandwidth of the AM signal is amplified, causing some of the sideband information to be lost and distortion results.
C) when the volume control is turned up to maximum, the desired station is very weak.
D) the tank circuits within the tuned amplifiers have too high a Q.

Question 12

If a receiver is overly selective:

A) the volume control is turned up to maximum, the desired station is very weak.
B) only part of the bandwidth of the AM signal is amplified, causing some of the sideband information to be lost and distortion results.
C) too much noise is picked up and amplified by the receiver.
D) the tank circuits within the tuned amplifiers have insufficient Q.

Question 13

The radio receiver that simply consists of an RF amplifier, detector, and audio amplifier is known as:

A) a sensitive receiver
B) a selective receiver
C) a TRF receiver
D) a superheterodyne receiver

Question 14

A padder capacitor:

A) is placed in an RF amplifier to provide for proper neutralization.
B) is placed in a tank circuit to provide for electronic tuning.
C) is placed in parallel with each section of the ganged capacitors of the tank to provide tracking at the high end of a large frequency band.
D) is placed in series with the tank inductor to provide tracking at the low end of a large frequency band.

Question 15

Diagonal clipping:

A) is characterized by having the capacitor voltage not follow the full changes of the envelope of the AM waveform.
B) occurs if the time constant of the low-pass filter is too large compared to the period of the RF waveform.
C) is a type of distortion that occurs with diode detectors.
D) all of the above

Question 16

The superheterodyne receiver design is superior to the TRF design:

A) since it uses many RF amplifier stages before the RF signal is mixed with the local oscillator signal.
B) since it allows for a constant selectivity over the entire tuning range of the receiver.
C) since it always uses synchronous detectors instead of diode detectors.
D) all of the above

Question 17

A trimmer capacitor:

A) is placed in an RF amplifier to provide for proper neutralization.
B) is placed in series with the tank inductor to provide tracking at the low end of a large frequency band.
C) is placed in a tank circuit to provide for electronic tuning.
D) is placed in parallel with each section of the ganged capacitor of the tank to provide tracking at the high end of a large frequency band.

Question 18

Synchronous detectors:

A) offer low distortion compared to diode detectors.
B) have the ability to provide gain.
C) are often called product detectors.
D) all of the above

Question 19

A receiver's sensitivity is:

A) its ability to drive the output speaker to an acceptable level.
B) the extent to which a receiver is capable of differentiating between the desired signal and other signals.
C) the ability of the receiver to demodulate a modulated signal.
D) the ability of a receiver to attenuate noise signals.

Question 20

An AM signal having a carrier frequency of 560 kHz is to be mixed with a local oscillator signal at a frequency of 1035 kHz. What does the output of the IF amplifier consist of?

A) a 475 kHz sinewave
B) the original intelligence signal
C) a 455 kHz carrier
D) a 475 kHz AM signal

Question 21

Electronics Workbench Multisim provides a feature that allows for the addition of a component fault in a circuit. This is accomplished by:

A) double-clicking on the component, select fault and specify the type of failure
B) replacing the part with a non model part
C) replacing the part with an F-prefix part
D) all of the above
E) none of the above

Question 22

The AGC control voltage:

A) varies as the signal strength of the received signal varies.
B) is actually the dc voltage component produced by the mixing action in the AM demodulator stage.
C) a negative feedback voltage.
D) is produced by an RC circuit having a much larger time constant than that of the detector.
E) all of the above

Question 23

An autodyne mixer is:

A) stage that mixes the LO with the AM signal without the use of a transistor.
B) mixer that uses a dual-gate FET.
C) stage that provides the mixing and generates the LO at the same time.
D) mixer that automatically provides for AGC action.

Question 24

Which of the following is not an advantage of FETs over BJTs in RF amplifier usage?

A) have improved image frequency rejection.
B) Their input/output square-law relationship allows for lower distortion levels.
C) The availability of dual gate FETs provides an isolated injection point for the AGC.
D) Their input impedance does not load down the Q of the circuit preceding the FET stage.

Question 25

A varicap:

A) is placed in a tank circuit to provide for electronic tuning.
B) is placed in series with the tank inductor to provide tracking at the low end of a large frequency band.
C) is placed in parallel with each section of the ganged capacitors of the tank to provide tracking at the high end of a large frequency band.
D) is placed in an RF amplifier to provide for proper neutralization.

Question 26

The reference level for the unit, dBm, is:

A) the milliampere
B) the milliwatt
C) the millivolt
D) the watt

Question 27

Double conversion is:

A) a technique used to reduce image frequency problems in a superheterodyne receiver.
B) a method that ensures that a superheterodyne receiver does not break into oscillations due to stray positive feedback.
C) a technique used to solve the TRF tuning problems.
D) a receiver design that uses two superheterodyne receivers to receive a weak signal.

Question 28

In a superheterodyne receiver the bulk of the receiver's sensitivity and selectivity is due to the:

A) IF amplifier stages.
B) local oscillator.
C) converter stages.
D) RF amplifier stages.

Question 29

A receiver has a maximum input signal of 75 mW before distortion occurs. Its sensitivity is measured to be 1.5 nW. Its dynamic range is approximately:

A) 47 dB
B) 77 dB
C) 87 dB
D) 154 dB

Question 30

Which of the following is not a major benefit of using RF amplifier stages in superheterodyne receiver design?

A) larger frequency tuning range
B) improved noise characteristics
C) improved image frequency rejection
D) more gain resulting in improved sensitivity

Question 31

Good troubleshooting practice says:

A) check the power supply voltages
B) prepare a trouble report
C) log the serial and model number
D) perform a visual check and check the power supply voltages
E) none of the above

Question 32

A receiver has a dynamic range of 65 dB. It has a sensitivity of 0.88 nW. The maximum allowable input signal is approximately:

A) 1.56 uW
B) 156 uW
C) 278 mW
D) 2.78 mW