REM A LVL 2

Question 1

Is known as the reflection of the signal
about the time origin n = 0

A. Scaling in the time domain
B. Folding the signal
C. Shifting

Answer 1

B. Folding the signal

Question 2

Signal manipulation that involves
replacing the independent variable n by
kn, where k is an integer

A. Scaling in the time domain
B. Shifting
C. Modulation
D. Folding the signal

Answer 2

A. Scaling in the time domain

Question 3

Which of the following is true for
complex-valued function?

A. ×(-t)=-x(t)
B. ×(-t)=x*(t)
C. x(-t)=x(t)

Answer 3

B. ×(-t)=x*(t)

Complex-valued function is said to be
conjugate symmetry if its real part is
even and imaginary part is odd and it is
shown by the equation x(-t)= x*(t).

Question 4

If the output of the system of the
system at any ‘n’ depends only the
present or the past values of the inputs
then the system is said to be_____

A. Non-causal
B. Non-Linear
C. Causal
D. Linear

Answer 4

C. Causal

A system is said to be causal if the
output of the system is defined as the
function shown below
y(n)=F[x(n),x(n-1),x(n-2)…] So,
according to the conditions given in the
question, the system is a causal
system.

Question 5

What is the process of increasing the
sampling rate by a factor l?

A. Interpolation
B. Sampling rate conversion
C. None of these choices
D. Decimation

Answer 5

A. Interpolation

The process of increasing the sampling
rate by an integer factor l, i.e., up-
sampling by l is called as interpolation.

Question 6

The systems that employ multiple
sampling rates are called multi-rate DSP
systems.

A. False
B. True
C. Partly true
D. Partly false

Answer 6

B. True

Systems that employ multiple sampling rates in the processing of digital signals are called multi rate digital signal
processing systems.

Question 7

Which of the following methods are
used in sampling rate conversion of a
digital signal?

A. D/A convertor, A/D convertor &
Performing entirely in digital domain
B. None of these choices
C. D/A convertor and A/D convertor

Answer 7

A. D/A convertor, A/D convertor &
Performing entirely in digital domain

Sampling rate conversion of a digital signal can be accomplished in one of the two general methods. One method is to pass the signal through D/A
converter, filter it if necessary, and then to resample the resulting analog signal at the desired rate. The second method is to perform the sampling rate
conversion entirely in the digital domain

Question 8

What is the process of reducing the
sampling rate by a factor D?

A. Sampling rate conversion
B. Decimation
C. Interpolation

Answer 8

B. Decimation

The process of reducing the sampling
rate by a factor D, i.e., down-sampling by
D is called as decimation.

Question 9

What is the number of filter coefficients that specify the frequency response for h(n) anti-symmetric?

A. (M-1)/2 when M is even and M/2 when M
is odd
B. (M+1)/2 when M is even and M/2 when M
is odd
C. (M-1)/2 when M is odd and M/2 when
M is even
D. (M+1)/2 when M is even and M/2 when M
is odd

Answer 9

C. (M-1)/2 when M is odd and M/2 when
M is even

For a anti-symmetric h(n) h(M-1/2)=0
and thus the number of filter
coefficients that specify the frequency response is (M-1)/2 when M is odd and M/2 when M is even.

Question 10

What is the value of h(M-1/2) if the unit
sample response is anti-symmetric?

A. -1
B. None of the mentioned
C. 1
D. 0

Answer 10

D. 0

When h(n)=-h(M-1-n), the unit sample
response is anti-symmetric. For M odd,the center point of the anti-symmetric is n=M-1/2. Consequently, h(M-1/2)=0.

Question 11

The roots of the equation H(z) must
occur in ____
A. Identical
B. Conjugate pairs
C. Zero
D. Reciprocal pairs

Answer 11

D. Reciprocal pairs

We know that the roots of the
polynomial H(z) are identical to the
roots of the polynomial H(z-1).
Consequently, the roots of H(z) must
occur in reciprocal pairs.

Question 12

What is the order of operations to be
performed in order to realize linear
phase lIR filter?
(i) Passing x(-n) through a digital filter H(z)
(ii) Time reversing the output of H(z)
(ii) Time reversal of the input signal x(n)
(iv) Passing the result through H(z)

A. (i),(iii),(iv),(ii)
B. (ii),(iii),(iv),(i)
C. (iii),(i),(ii),(iv)
D. (ii),(i),(iv),(iii)

Answer 12

C. (iii),(i),(ii),(iv)

If the restriction on physical reliability is removed, it is possible to obtain a linear phase IIR filter, at least in principle. This approach involves performing a time
reversal of the input signal x(n), passing
x(-n) through a digital filter H(z), time
reversing the output of H(z), and finally,
passing the result through H(z) again.

Question 13

Which is an incorrect statement about
FIR filters?

A. FIR filters are always stable.
B. FIR filters are not immune to noise.
C. Its realization can be done using non-
recursive structures.

Answer 13

B. FIR filters are not immune to noise.

FIR filters are highly immune to noise.

Question 14

Fourier analysis helps us to determine
how much bandwidth a particular signal
occupies.

A. True
B. Partly false
C. Partly true
D. False

Answer 14

A. True

Fourier analysis allows us to determine not only the sine wave components in any complex signal but also how much bandwidth a particular signal occupies. Although a sine or cosine wave at a
single frequency theoretically occupies
no bandwidth, complex signals
obviously take up more spectrum
space.

Question 15

Which is an incorrect statement about
the impulse invariant method?

A. It can easily convert discrete filters into
analog filters.
B. No warping effect.
C. It preserves the frequency characteristics.
D. Absence of many-to-one mapping.

Answer 15

D. Absence of many-to-one mapping.

The presence of many-to-one mapping is a primary drawback of the impulse invariant method. It means that many points in the s-plane are mapped to a single point in the z-plane. It can also cause an aliasing effect in the filters.

Question 16

Linear phase response of the filter is
defined as

A. When the phase response of the system does not vary linearly with the frequency function.
B. None of these choices
C. When the phase response of the
system varies linearly with the
frequency function.
D. When the phase response of the system
varies inversely with the frequency
function.

Answer 16

C. When the phase response of the
system varies linearly with the
frequency function.

As the name specifies, the phase
response of the system varies linearly
with the frequency.

Question 17

The F.T. of a conjugate symmetric
function is always

A. real
B. conjugate symmetric
C. imaginary
D. conjugate asymmetric

Answer 17

A. real

F.T. of conjugate symmetric function is
always real.

Question 18

Which of the following is/are incorrect about the Cascade realization of the IIR systems?

A. It is helpful in determining the overall
transfer function.
B. The filters in the cascade are
connected in parallel.
C. It requires less amount of energy.
D. It is helpful in determining the overall
transfer function.

Answer 18

B. The filters in the cascade are
connected in parallel.

The filters in the cascade realization are
connected in series.

Question 19

According to Nyquist, the impulse
response of the overall communication
system should have _____ decay with _____
magnitude for sample values not
equal to zero.

A. Slow, large
B. Fast, Large
C. Slow, small
D. Fast, small

Answer 19

D. Fast, small

According to Nyquist, the impulse
response of the overall communication
system should have fast decay with
small magnitude for sample values not
equal to zero. If the channel is ideal,
then it should be possible to realize approximate shaping filters at both transmitter and receiver.

Question 20

The unit decibel is a way of expressing
the hearing response of the human ear.

A. True
B. Partly true
C. Partly false
D. False

Answer 20

A. True

The gain or loss of a circuit is usually expressed in decibels (dB), a unit of measurement that was originally
created as a way of expressing the
hearing response of the human ear to various sound levels. A decibel is onetenth of a bel.

Question 21

The input power to the final stage of
your transmitter is 200 watts and the
output is 125 watts. What has happened
to the remaining power?

A. It has been used to provide greater
efficiency
B. It has been dissipated as heat loss
C. It has been used to provide negative
feedback
D. It has been used to provide positive
feedback

Answer 21

B. It has been dissipated as heat loss

Power Amplifiers have a certain
lefficiency’, the ratio of DC power
required to obtain an RF output. The
difference goes up in heat. This is the reason for the ‘heat sinks’ on the back of transmitters

Question 22

Musical instruments makes sounds
usually in what range?

A. LF
B. VLF
C. MF
D. HF

Answer 22

B. VLF

Question 23

Which of the following has an operation
bandwidth?

A. all of these choices
B. audio amplifier
C. antennas
D. AM Radio Receivers

Answer 23

A. all of these choices

Bandwidth - The frequency range over
which an information signal is
transmitted or over which a receiver or
other circuits operates. As long as a
device, equipment, or system has limits
of its frequency of operation, it has an
operating BANDWIDTH. Amplifiers,
radio receivers, antennas, filters,
transmission media, etc. has operation
bandwidth.

Question 24

Which of the following has the widest
bandwidth?

A. audio amplifiers
B. FM broadcast station
C. TV broadcast station
D. AM broadcast station

Answer 24

C. TV broadcast station

Audio amplifiers - operates only at the range of sound from 20Hz to 20,000Hz thus a bandwidth of ~20,000Hz

AM broadcast station - bandwidth for international standards is at 10,000 Hz(10 kHz) per station

FM broadcast station - bandwidth for
international standards is at 200,000 Hz
(200 KHz) per station

TV broadcast station - bandwidth for international standards is at 6,000,000 Hz (6 MHz) per station

Question 25

Is that portion of the electromagnetic spectrum occupied by a signal. A. Power B. Frequency C. Wavelength D. Bandwidth

Answer 25

D. Bandwidth Frequency - It is simply the number of times a particular phenomenon occurs in a given period of time. Wavelength - The distance traveled by an electromagnetic wave during the time of 1 cycle. Bandwidth -The frequency range over which an information signal is transmitted or over which a receiver or other circuits operates. Power - it is the rate at which energy is dissipated or consumed.

Question 26

For a ____ channel, we need to use the Shannon capacity to find the maximum bit rate. A. low-pass B. noiseless C. noisy

Answer 26

C. noisy

Question 27

What will happen to the shot noise current if from the frequency of 100 kHz is increased to 300 kHz keeping all other parameters constant? A. nothing will happen B. increases C. decreases D. remains the same

Answer 27

A. nothing will happen Shot Noise current Equation: I_N=√2Blq Where: In = Shot noise current in Amperes I = DC current flowing in Amperes q = electron charge (1.602x101-19 C or constant 23 in your calculator) B = bandwidth in Hertz Based on the Shot noise current formula above, only the bandwidth and flowing DC current affect the shot noise. Changing the spectrum won't change the frequency which in effect cannot affect shot noise, therefore 'nothing will happen' is the answer.

Question 28

Which of the following is classified as Correlated noise? A. flicker noise B. harmonic distortion C. shot noise D. white noise

Answer 28

B. harmonic distortion There are two categories of noise, the correlated and the uncorrelated noise. Correlated noise are internal noise that can only exist if there is a signal/ information present. Noise such as harmonic distortion and intermodulation distortion are some examples. The uncorrelated noise can be both external and internal types that can be present whether there is a signal/ information present or not. Thermal noise, shot noise, flicker noise, industria noise, atmospheric noise, solar noise, etc., are some examples.

Question 29

Which of the following does not affect shot noise current? A. DC current B. bandwidth C. frequency D. none of these choices

Answer 29

C. frequency Shot Noise current Equation: I_N=√2BIq Where: In = Shot noise current in Amperes I = DC current flowing in Amperes q = electron charge (1.602x10^-19 C or constant 23 in your calculator) B = bandwidth in Hertz Based on the Shot noise current formula above, only the bandwidth and flowing DC current affect the shot noise curret.Therefore we choose 'frequency' as the answer.

Question 30

Shot noise is a A. Poisson process B. None of these choices C. Stochastic process

Answer 30

A. Poisson process

Question 31

Shot noise is produced by A. Protons B. Electrons C. Electrons & protons

Answer 31

C. Electrons & protons Shot noise occurs due to particle like the behaviour of electron and photon.

Question 32

The value of resistor creating thermal noise is doubled. The noise power generated therefore A. doubled B. halved C. quadrupled D. unchanged

Answer 32

D. unchanged Noise power is not dependent on resistance. Pn=KTB

Question 33

The value of a resistor creating thermal noise is doubled. The noise power generator is therefore A. Quadrupled B. Halved C. Doubled D. Unchanged

Answer 33

D. Unchanged The thermal noise of a noisy resistor is proportional to bandwidth and temperature only, hence the power remains unchanged even if we double the values of given resistors.

Question 34

Burst noise affects FM systems. A. Partly false B. False C. True D. Partly true

Answer 34

B. False If the FM received signal is above the FM threshold, burst noise does not affect FM system performance as much as AM systems. It is due to the fact that message amplitude variations do not carry information in FM.

Question 35

Intermodulation distortion is classified as Correlated Noise, this is because: A. sum and difference frequencies can only be present if there is a signal present B. sum and difference frequencies are present everywhere C. sum and difference frequencies can be present whether there is a signal present or not

Answer 35

A. sum and difference frequencies can only be present if there is a signal present There are two categories of noise, the correlated and the uncorrelated noise. Intermodulation distortion is classified as Correlated Noise because sum and difference frequencies are products of mixing where a signal is mixed with the local oscillator frequency. Without a signal, there are no sum and difference frequencies and intermodulation distortion cannot exist. Correlated noise are noise that can only be present if there is a signal/ information present, whereas the uncorrelated noise are noise that can be present whether there is a signal/information present or not. In short, correlated noise are always related to the signal.

Question 36

Shot noise is avoidable when current is A. Zero B. Infinity C. None of these choices D. One

Answer 36

A. Zero Shot noise is avoidable only when the current is zero.

Question 37

Which of the following generates more noise power at a uniform temperature? A. TV station broadcast band B. AM station broadcast band C. FM station broadcast band D. both AM and FM broadcast bands

Answer 37

A. TV station broadcast band Thermal Noise Power Equation: N=kTB Where: N= noise power in Watts T= temperature in Kelvin B = bandwidth in Hertz k = Boltzmann's constant = 1.38064852 × 10^-23 JK^-1 (constant 25 in your calculator) Based on the Noise Power formula above, as the temperature is kept constant, the noise power changes proportionately as the bandwidth changes. An AM station has a bandwidth of 10 kHz, an FM station has 200kHz, and a TV station has a bandwidth of 6MHz. The TV station has the largest bandwidth among the choices therefore will have the greatest generation of Thermal noise power.

Question 38

A frequency that is an integer multiple of the fundamental frequency. A. fundamental frequency B. harmonic frequency C. 2nd harmonic D. 3rd harmonic

Answer 38

B. harmonic frequency Fundamental frequency is defined as the lowest frequency of a periodic waveform and also referred as the first harmonic. Harmonics are frequencies that are integer multiples of the fundamental frequency. Examples: The 1 harmonic of 1Hz is 1x1Hz which is 1Hz (which is the same as its fundamental frequency) The 2 harmonic of 1 Hz is 2x1Hz which is 2Hz. The 3 harmonic of 1 Hz is 3x1Hz which is 3Hz. The 100 harmonic of 1 Hz is 100x1Hz which is 100Hz.

Question 39

What is the usual bandwidth of a single- sideband amateur signal? A. Between 2 and 3 kHz B. Between 3 and 6 kHz C. 2kHz

Answer 39

A. Between 2 and 3 kHz By transposing the voice signal into the radio spectrum, the SSB transmitter manages to only use the approximate bandwidth of the original modulation(speech frequencies important to communications span 300 Hertz to 3000 Hertz, a bandwidth of 2700 Hertz ). SSB uses half the bandwidth of AM.

Question 40

Frequency modulated signal is regarded as the phase modulated signal in which the modulating wave is differentiated before modulation. A. True B. Partly true C. False

Answer 40

C. False Frequency modulated signal is regarded as the phase modulated signal in which the modulating wave is integrated before modulation. This means that an FM signal can be generated by first integrating the message signal and then using the result as an input to a phase modulator.

Question 41

In standard AM transmitter, which of the following supplies the energy which is required to drive the antenna system at the rated RF power for high-level modulation? A. Modulated Power Amplifier B. Buffer Amplifier C. Crystal Oscillator D. Intermediate Power Amplifier

Answer 41

A. Modulated Power Amplifier Modulated Power Amplifier - a class C RF amplifier that supplies the energy which is required to drive the antenna system at the rated RF power for high level modulation. It multiplies the signals from the IF power amplifier and push-pull modulator.

Question 42

The spectrum space occupied by a DSB signal is the same as that of a conventional AM signal. A. False B. Partly true C. True

Answer 42

C. True DSB or double sideband suppressed carrier does not alter the maximum and minimum frequency of the signal. It only suppressed the carrier signal and hence the spectrum space which is dependent on frequency remains unchanged.

Question 43

Single sideband AM systems occupy same bandwidth as of conventional AM systems. A. Partly true B. False C. True

Answer 43

B. False Single sideband (SSB) AM systems transmit only one of the sidebands (either upper or lower) about the carrier. Hence, they occupy only half the bandwidth of conventional AM systems.

Question 44

If the peak message signal amplitude is half the peak amplitude of the carrier signal, the signal is____ modulated. A. 2% B. 100% C. 50% D. 70% E. 90%

Answer 44

C. 50% The modulation is also expressed in percentage. It is also called percentage modulation. The signal is said to be 50%modulated if the peak message signal amplitude is half the peak amplitude of the carrier signal.

Question 45

Which of the following is an advantage of SSB over DSB? A. Reduce in spectrum space B. No change in spectrum space C. Power is not wasted on the carrier D. Carrier is suppressed

Answer 45

A. Reduce in spectrum space In a signal, only the sidebands contain the information. Also, there is a duplication of the information in each sideband. Thus one sideband is sufficient form transmission as compared to DSB where both the sidebands are present. Since one of the sideband is also suppressed it reduces the maximum or the minimum frequency of the signal and hence the spectrum space is reduced in an SSB

Question 46

What is the modulation index for the FM to behave as a narrowband? A. 0.10 B. 1 C. 0.25 D. 0.10

Answer 46

C. 0.25 When the modulation index is around 0.25 the modulation produces only single pairs of significant sidebands like that of AM. This occupies comparatively less spectrum space.

Question 47

What may your FM hand-held or mobile transceiver do if you shout into its microphone? A. It may cause interference to other stations operating near its frequency B. It may cause atmospheric interference in the air around the antenna C. It may cause interference to other stations operating on a higher frequency band D. It may cause digital interference to computer equipment

Answer 47

A. It may cause interference to other stations operating near its frequency SHOUT. 'Overdeviation (FM)' or 'Overmodulation (AM,SSB)' results in distorted speech plus using excessive bandwidth on the air (splatter) and interfering with stations using adjacent frequencies ('out-of-channel emissions').

Question 48

FM bandwidth is approximated using ___ rule. A. Carson's B. Faraday's C. Maxwell's D. Armstrong's

Answer 48

A. Carson's

Question 49

Why is no carrier signal transmitted when the amplitude of the modulating signal is 0 in an SSB transmission? A. Undermodulation B. No sideband is generated C. All the sideband is suppressed D. Attenuation

Answer 49

B. No sideband is generated In an SSB the carrier signal is suppressed. Also, only when a modulating signal is present the sideband is produced. When there is no modulating signal there is no sideband produced and the carrier is also suppressed hence nothing is transmitted.

Question 50

Indicate the false statement. Modulation is used to A. reduce the bandwidth used B. allow the use of practicable antennas C. separate differing transmissions

Answer 50

A. reduce the bandwidth used The modulation process will increase the bandwidth of the system.

Question 51

In FM, the sideband is significant if it is at least greater than or equal to ____ of the peak carrier voltage. A. 20% B. 1% C. 5%

Answer 51

B. 1% In AM, there are only two sidebands. In FM, there are infinite number of sidebands, so the ideal bandwidth FM is also infinite, however, other sidebands are insignificant so they are neglected. The sideband is significant if it is at least greater than or equal to the 1% of the peak carrier voltage. The sideband is insignificant if it is less than 1% of the peak carrier voltage.

Question 52

One of the following cannot be used to remove unwanted sideband in SSB. This is the A. Filter system B. Balanced modulator C. Third method D. Phase Shift

Answer 52

B. Balanced modulator Generation of SSB: Filter Method - it uses LC, crystal, ceramic or mechanical filters to eliminate one of the sidebands of the SSB. Phase Shift Method - make use of two balanced modulators and two phase shifters. Third (Weaver) Method - retains the advantages of the phase shift method without the disadvantage of the AF phase shift method.

Question 53

FM uses class ___ amplifiers and AM uses class ___ amplifiers. A. AB, C B. C, A C. C, C D. A, C

Answer 53

B. C, A The constant envelope of the transmitted signal allows efficient class C amplifiers. However, in AM, it is critical to maintain linearity between the applied message and amplitude of transmitted signal. Therefore, class A or AB are used for AM systems.

Question 54

Frequency multiplier multiplies the frequency deviation produced by the modulator. A. Partly false B. True C. Partly true D. False

Answer 54

B. True The frequency multiplier increase the carrier frequency to the desired output frequency, but also it multiples the frequency deviation produced by the modulator. The design of the transmitter must be such that the frequency multipliers will provide the correct amount of multiplication not only for the carrier frequency but also for the modulation deviation.

Question 55

In angle modulation, signal to noise ratio before detection is a function of A. IF filter bandwidth B. Maximum frequency of the message C. Input signal to noise ratio D. Modulation index

Answer 55

A. IF filter bandwidth In angle modulation systems, the signal to noise ratio before detection is the function of the receiver IF filter bandwidth, received carrier power, and received interference. However, signal to noise ratio after detection is a function of maximum frequency of the message, input signal to noise ratio and modulation index.

Question 56

Image frequency problems would be reduced by. A. none of these choices B. having a narrowband RF amplifier before the mixer C. having a wideband RF amplifier after the mixer D. having an IF amplifier with the proper shape factor

Answer 56

B. having a narrowband RF amplifier before the mixer Image frequency is defined as any frequency other than the selected radio frequency carrier that, if allowed to enter a receiver and mix with local oscillator will produce a cross-product frequency that is equal to intermediate frequency.

Question 57

Non coherent detection requires the knowledge of transmitted carrier frequency and phase at the receiver. A. True B. False C. Partly false D. Partly true

Answer 57

B. False Non coherent detection does require the knowledge of phase information. However, coherent detection requires knowledge of the transmitted carrier frequency and phase at the receiver.

Question 58

What is the purpose of a buffer amplifier stage in a transmitter? A. It prevents transmitters from producing spurious frequencies in the output signals. B. It amplifies audio frequencies before modulation occurs. C. Its high input impedance prevents oscillators from drifting off frequency. D. It provides power amplification with high efficiency.

Answer 58

C. Its high input impedance prevents oscillators from drifting off frequency. Buffer Amplifier - a class A RF amplifier that isolates the crystal oscillator to improve its stability. It is connected after the oscillator to prevent it from loading (changing value of load voltage). It has a high input impedance and low output impedance (commoncollector or emitter-follower configuration) to couple the high output impedance of the oscillator and the low input impedance of the IF power amplifier.

Question 59

The components of TRF includes the following, except: A. Detector B. AF Amplifier C. Mixer

Answer 59

C. Mixer Components of TRF. Antenna RF Amplifier - it amplifies the weak RF signal. Detector - it extracts the information. AF Amplifier - it amplifies the weak AF signal.

Question 60

Any frequency other than the selected radio frequency carrier that, if allowed to enter a receiver and mix with the local oscillator, will produce a cross-product frequency that is equal to the intermediate frequency A. Tuned Radio Frequency B. None of these choices C. Both of these choices D. Image Frequency

Answer 60

D. Image Frequency Image Frequency is any frequency other than the selected radio frequency carrier that, if allowed to enter a receiver and mix with the local oscillator, will produce a cross-product frequency that is equal to the intermediate frequency.

Question 61

In superhet, which is considered as the first detector? A. Detector B. RF Amplifier C. Mixer D. IF Section

Answer 61

C. Mixer Mixer - it is the first detector which operates in a non-linear fashion and provides the action which produces the desired intermediate frequency. The output of a mixer includes the original, sum and difference of the local oscillator frequency and the RF input frequency.

Question 62

Frequency demodulator is a frequency to amplitude converter circuit. A. False B. Partly true C. True D. Partly false

Answer 62

C. True Frequency demodulator produces an output voltage with instantaneous amplitude that is directly proportional to the instantaneous frequency of the input FM signal. Thus, frequency demodulator is a frequency to amplitude converter circuit.

Question 63

A ___ sine wave is not useful in data communications; we need to send a ___ signal. A. none of these choices B. single-frequency; composite C. double-frequency; composite D. all of these choices

Answer 63

B. single-frequency; composite

Question 64

Intersymbol interference (ISI) leads to ___ probability of the receiver for making an error in detecting the symbols. A. Decreased B. Increased C. One D. Zero

Answer 64

B. Increased ISI leads to increased probability of the receiver making an error in detecting a symbol. When rectangular pulses are passed through a bandlimited channel,the pulses will spread in time, and the pulse for each symbol will smear into the time intervals of succeeding symbols.

Question 65

Modern mobile communication systems use analog modulation techniques. A. True B. False

Answer 65

B. False Modern mobile communication systems use digital modulation techniques. Advancements in VLSI and digital signal processing technology have made digital modulation more cost effective than analog transmission systems.

Question 66

An intricate part of electronic communications system because of its up- and down-conversion functions as they are transported through a channel. A. demodulation B. oscillation C. translation D. modulation

Answer 66

C. translation Oscillation is the continuous recurrence of the same electrical periodic waveform Modulation is the process of varying one or more properties of a high frequency periodic waveform, called the carrier signal, with respect to a modulating signal. Demodulation is the act of extracting the original information-bearing signal from a modulated carrier wave. A demodulator is an electronic circuit used to recover the information content from the modulated carrier wave

Question 67

Half power bandwidth is also called A. Absolute bandwidth B. Zero dB bandwidth C. Null to null bandwidth D. 3 dB bandwidth

Answer 67

D. 3 dB bandwidth Half power bandwidth is also called the 3 dB bandwidth. It is defined as the interval between frequencies at which the PSD has dropped to half power, or 3 dB below the peak value.

Question 68

A desirable modulation scheme provides ___ bit error rates at ___ received signal to noise ratios. A. Low, low B. High, high C. Low, high D. High, low

Answer 68

A. Low, low A desirable modulation scheme provides low bit error rates at low received signal to noise ratios. They perform well in multipath and fading conditions, occupies a minimum bandwidth and is easy and cost effective to implement.

Question 69

_____ is equal to width of main spectral lobe. A. Null to null bandwidth B. Absolute bandwidth C. Half power bandwidth D. 3 dB bandwidth

Answer 69

A. Null to null bandwidth Null to null bandwidth is a simpler and more widely accepted measure of bandwidth. It is equal to the width of main spectral lobe.

Question 70

Which of the following is not an advantage of digital modulation? A. Greater noise immunity B. Less bandwidth requirement C. Easier multiplexing D. Greater security

Answer 70

B. Less bandwidth requirement Digital modulation offers many advantages over analog modulation. Some advantages include greater noise immunity and robustness. They provide easier multiplexing of various forms of information and greater security.

Question 71

Capacity of a channel can be increased by A. None of these choices B. Increasing channel bandwidth &signal power C. Increasing channel bandwidth D. Increasing signal power

Answer 71

B. Increasing channel bandwidth &signal power Capacity of a channel can be increased by increasing channel bandwidth and also by increasing signal power.

Question 72

In digital communication system, in order to increase noise immunity, it is necessary to increase A. Signal frequency B. Signal amplitude C. Signal power

Answer 72

C. Signal power In digital communication system, in order to increase noise immunity, it is necessary to increase signal power. However, the amount by which the signal power should be increased to obtain a certain level of fidelity depends on the particular type of modulation employed.

Question 73

Which of the following is defined as the range of frequencies over which the signal has a non-zero power spectral density? A. Absolute bandwidth B. 3 dB bandwidth C. 5 dB bandwidth

Answer 73

A. Absolute bandwidth The absolute bandwidth is defined as the range of frequencies over which the signal has a non-zero power spectral density. For symbols represented as rectangular baseband pulses, the PSD profile extends over an infinite range of frequencies, and has an absolute bandwidth of infinity.

Question 74

The performance of modulation scheme is not measured in terms of A. Transmitted power B. Power efficiency C. Cost and complexity D. Transmitted energy

Answer 74

A. Transmitted power The performance of modulation scheme is often measured in terms of its power efficiency and bandwidth efficiency. Other factors also affect the choice of modulation scheme, such as cost and complexity of the subscriber receiver and modulation which is simple to detect.

Question 75

Oscillators that are not self-sustaining are called ___ A. triggered B. feedback C. regenerative D. free-running

Answer 75

A. triggered Free-running oscillator is also known as astable multivibrator Positive or regenerative feedback is used for oscillators

Question 76

In a _____ handoff, a mobile station only communicates with one base station. A. none of these choices B. medium C. hard D. soft

Answer 76

C. hard

Question 77

SQNR can be improved by_____ sampling rate. A. None of these choices B. Increasing C. Does not depend D. Decreasing E. All of these choices

Answer 77

B. Increasing SQNR can be improved by increasing the sampling rate.

Question 78

Which of the following is the ratio of signal energy per bit to noise power spectral density? A. Power efficiency B. Power density C. Spectral density D. Bandwidth efficiency

Answer 78

A. Power efficiency Power efficiency is often expressed as the ratio of signal energy per bit to noise power spectral density required at the receiver input for a certain probability of error. Power efficiency is a measure of how favorably the trade-off between fidelity and signal power is made.

Question 79

____ is the picture portion of a commercial television broadcasting signal. A. VSB System B. Bandwidth C. Sideband D. None of these choices

Answer 79

A. VSB System VSB System is the picture portion of a commercial television broadcasting signal.

Question 80

Increasing the data rate implies the increase in pulse width of digital symbol. A. Partly true B. False C. True D. Partly false

Answer 80

B. False There is an unavoidable relationship between data rate and bandwidth occupancy. Increasing the data rate implies decreasing the pulse width of a digital symbol, which increases the bandwidth of the signal.

Question 81

Which of the following is true with respect to the bandwidth of a 2kHz audio signal and a 2kHz binary data? A. Bandwidth keeps increasing with time for the binary data B. Bandwidth is higher for binary data than audio signals C. Bandwidth is higher for audio signals than binary data D. Bandwidth remains the same for both

Answer 81

B. Bandwidth is higher for binary data than audio signals Since binary data is transmitted in square waves or pulses, they are generally made up of numerous fundamental sine waves. This occupies a huge bandwidth as compared to audio signals which are analog in nature and usually comprise of a lesser number of sine waves.