Deck 8: Digital Modulation and Demodulation

Question 1

The two forms of spread spectrum are frequency hopping and ______________.
A.direct sequence
B.continuous wave
C.spectral regrowth
D.voltage controlled

Answer 1

direct sequence

Question 2

The _____________ gives a visual indication of system linearity and noise performance.
A.spread spectrum
B.pseudonoise
C.spectral regrowth
D.constellation pattern

Answer 2

constellation pattern

Question 3

Why must modulated signals be demodulated?
A.To recover the original intelligence
B.To improve the spectral efficiency of digital transmissions
C.To enable implementation of advanced features
D.To produce one or more significant sideband pairs

Answer 3

To recover the original intelligence

Question 4

The term "M-ary" in M-ary modulation derives from the word ___________.
A.binary
B.baud
C.bit
D.bandwidth

Question 5

The ________ demodulator reverses the process of modulation,thereby recovering the original binary data signal.
A.QAM
B.ISM
C.FSK
D.BER

Question 6

Excessive _______ means that a receiver cannot differentiate one symbol from another.
A.noise
B.ISI
C.modulation
D.frequencies

Question 7

Each form of digital modulation has implications in terms of spectral efficiency,power distribution,and _________.
A.amplitude
B.bandwidth
C.performance
D.distortion

Question 8

What is one advantage provided by a phase-shift keying (PSK)system?
A.Improved noise performance
B.Better ionospheric fading characteristics
C.Low probability of error
D.Transmitter frequency is constantly changing

Question 9

Which of the following achieves high spectral efficiencies because the spacing of each carrier is as close as theoretically possible?
A.Direct-sequence spread spectrum (DSSS)
B.Quadrature amplitude modulation (QAM)
C.Orthogonal frequency-division multiplexing (OFDM)
D.Code-division multiple access (CDMA)

Question 10

What type of transmissions represented the first type of digital communications?
A.Digital signal processing
B.Amplitude-shift keying
C.Morse code
D.On-off keying

Question 11

Which of the following filters has the important property that its impulse response rings at the symbol rate,which means that it is capable of minimizing ISI?
A.Bandpass
B.Low-pass
C.Raised-cosine
D.Gaussian

Question 12

What type of coding is used to minimize data errors in the data transmission process?
A.On-channel
B.Channel
C.In band
D.Multiple access

Question 13

The advantage of a differential phase-shift keying (DPSK)system is that_____________ is (are)not required.
A.carrier synchronizer
B.voltage-controlled oscillators
C.upper and lower sidebands
D.carrier recovery circuitry

Question 14

What type of receiver detects the phase shift in the received signal?
A.Binary phase-shift keying
B.Quadrature phase-shift keying
C.Differential phase-shift keying
D.Frequency-shift keying

Question 15

Which of the following is the basis for cellular systems employing the code-division multiple access (CDMA)standard?
A.COFDM
B.QPSK
C.OFDM
D.DSSS

Question 16

What requirements for a data stream depend on the encoding method used to transmit the data?
A.Frequency
B.Noise
C.Bandwidth
D.Baud rate

Question 17

Why are signals that are in quadrature said to be orthogonal?
A.They do not interfere with each other.
B.They split into two paths.
C.They can shift to one of two predetermined phase states.
D.The amount of data that can be transmitted over time.

Question 18

Where is minimum-shift keying (MSK)widely used?
A.Radios
B.Cordless phones
C.Military applications
D.Garage-door openers

Question 19

Which of the following is a key characteristic of orthogonal frequency-division multiplexing?
A.Amplitude modulation
B.Noise performance
C.Digital modulation
D.Spectral efficiency

Question 20

When a carrier is conveying intelligence by simply turning it on or off according to a prearranged code,this type of transmission is called ____________.
A.continuous wave
B.sine wave
C.square wave
D.cosine wave

Question 21

The power of DSSS systems is largely in the spreading and dispreading of the received signal because it gives rise to a phenomenon known as ______________.
A.channel coding
B.spectral regrowth
C.processing gain
D.frequency-hopping

Question 22

What law allows us to predict the minimum bandwidth required for information transfer in a given time interval?
A.Ohm's
B.Gaussian's
C.Fourier's
D.Hartley's

Question 23

OFDM modulation is essentially the converse of ____________.
A.demodulation
B.efficiency
C.high data rates
D.interference

Question 24

Impedance is an AC quantity is composed of both resistance and ______________.
A.complexity
B.reactance
C.magnitude
D.expression

Question 25

A sine or cosine wave can be thought of as consisting of both positive and negative ______________.
A.frequencies
B.signals
C.ranges
D.carriers