Deck 6: Frequency Modulation: Reception

Question 1

The term "quadrature" in a quadrature detector refers to:

A) their use in producing four-channel stereo detection
B) the fact that it was the fourth FM detector design to gain popularity
C) the fact that the two input signals to the exclusive-or gate are 90 degrees out of phase with one another
D) the fact that a four input gate is part of the detector stage

Answer 1

C

Question 2

Which of the following FM discriminators produces excessive distortion due to its nonlinear roll-off characteristics?

A) quadrature detector
B) PLL detector
C) ratio detector
D) Foster-Seely detector
E) slope detector

Answer 2

E

Question 3

A limiter stage in an FM receiver functions to

A) filter out any cross modulation frequency components produced by the mixer stage
B) limit the amount of frequency deviation in the received FM signal
C) remove any residual amplitude modulation in the RF signal before being fed to the detector stage
D) reduce noise produced by transistors in the RF and IF amplifier stages

Answer 3

C

Question 4

The basic difference between the block diagram of an AM receiver and FM receiver is that

A) an FM receiver must use automatic frequency control
B) an FM receiver does not use the superheterodyne design
C) an FM receiver uses a limiter and discriminator instead of a diode detector
D) an FM receiver cannot ever use automatic gain control

Question 5

Which of the following does not occur in a limiter stage found in an FM receiver?

A) amplifying a signal with an easily overdriven amplifier
B) recreating the intelligence signal
C) clipping action of the FM signal
D) recreating the FM sinewave due to the flywheel effect

Question 6

When a PLL is set up as an FM detector, the input FM signal is applied to the input of

A) the low-pass filter of the PLL
B) the frequency multiplier of the PLL
C) the phase detector of the PLL
D) the VCO of the PLL

Question 7

A PLL is set up so that its VCO free-runs at 8.9 MHz. The VCO does not change frequency unless its input is within plus or minus 75 kHz of 8.9 MHz. After it does lock, the input frequency can be adjusted within plus or minus 120 kHz of 8.9 MHz without having the PLL start to free-run again. The tracking range of the PLL is:

A) 240 kHz
B) 75 kHz
C) 120 kHz
D) 150 kHz

Question 8

The measure of how much signal is required in an FM receiver to produce a specific level of quieting is referred to as:

A) the receiver's noise reduction
B) the receiver's stereo separation
C) the receiver's sensitivity
D) the receiver's selectivity

Question 9

A form of receiver noise called cross modulation is caused by

A) noise caused by the mixer
B) noise caused by using non-square law device
C) noise caused by high impedance device
D) noise caused by using JFETs

Question 10

A standard IF frequency in FM receivers is:

A) 4.5 MHz
B) 9.0 MHz
C) 10.7 MHz
D) 455 kHz

Question 11

Which of the following stages is not a building block of a phase-lock loop?

A) low-pass filter
B) phase comparator
C) frequency multiplier
D) voltage-controlled oscillator

Question 12

In FM reception, the circuitry used to extract the intelligence from the carrier is:

A) limiter.
B) discriminator.
C) VCO.
D) Crosby modulator.

Question 13

Input into the PLL is at the:

A) comparator circuit.
B) low-pass filter.
C) VCO.
D) phase detector.

Question 14

The FM detector that can be implemented using digital exclusive-or gates is the

A) slope detector
B) quadrature detector
C) PLL FM detector
D) Foster-Seely design
E) ratio detector

Question 15

Which of the following FM detectors is a classical design dating back to vacuum tube technology?

A) quadrature detector
B) diode detector
C) Foster-Seely detector
D) PLL detector

Question 16

The square-law FET characteristics

A) reduces the shot noise produced by the FET
B) minimize the cross-modulation distortion in an FM receiver
C) allow for narrower bandwidth in the tuned amplifier that it is used in
D) allow for greater sensitivity in an FM receiver

Question 17

The ratio detector design is superior to the Foster-Seely design in that:

A) it uses less diodes than does the Foster-Seely design
B) it offers superior linear response to wideband FM deviation
C) it can be built using digital integrated circuits
D) amplitude changes in the input FM signal have no effect on the output

Question 18

The minimum required voltage for limiting is called

A) quieting.
B) limiting knee.
C) threshold.
D) all of the above

Question 19

Which of the following does provide amplitude limiting?

A) PLL
B) Foster-Seely discriminator
C) ratio detector
D) all of the above

Question 20

Why do most quality FM receivers employ FETs in their RF amplifiers?

A) FETs have a superior frequency response
B) FETs have a very low input capacitance
C) FETs have a square-law input/output relationship
D) FETs have a very high input impedance

Question 21

In an FM stereo receiver, what is the purpose of the AM detector stage?

A) It mixes the L+R and L-R signals to produce separate L and R audio signals
B) It converts the L-R DSB signal back into an L-R signal at audio frequencies
C) It converts the L+R DSB signal back into an L+R signal at audio frequencies
D) It filters out the 19 kHz pilot carrier from the complex discriminator output signal

Question 22

An example of an FM stereo demodulator integrated circuit is the:

A) 560.
B) 3090.
C) 3089.
D) 565.

Question 23

In an FM stereo receiver, what is the purpose of the matrix network?

A) to filter out the L-R signal at the output of the discriminator
B) to produce separate L and R signals from the L+R and L-R signals
C) to filter out the SCA signal at the output of the discriminator
D) to filter out the L+R signal at the output of the discriminator

Question 24

In an FM stereo receiver, why is there a frequency doubler stage in the stereo demodulation section?

A) It doubles the frequency of the L+R audio signals
B) It is part of the FM discriminator stage
C) It doubles the 19 kHz pilot carrier so that the AM detector will work properly
D) It is required in the de-emphasis network

Question 25

The FM detector design that does not require intricate coil adjustments to be tuned is the:

A) Foster-Seely detector
B) PLL detector
C) quadrature detector
D) slope detector
E) ratio detector

Question 26

When a PLL is set up as an FM detector, the output intelligence signal appears at the output of

A) the VCO of the PLL
B) the low pass filter of the PLL
C) the frequency multiplier of the PLL
D) the phase detector of the PLL

Question 27

The expected output frequency of a mixer circuit with an input frequency of 92.1 MHz and a local oscillator frequency of 102.8MHz is:

A) 194.9 MHz
B) 11.7 MHz
C) 10.1 MHz
D) 9.7 MHz
E) none of the above