REM A LVL 2 Flashcards

Question 1

Q

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

A

B. Folding the signal

Question 2

Q

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

A

A. Scaling in the time domain

Question 3

Q

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

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

Answer

A

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

Q

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

A

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

Q

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

A

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

Q

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

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

Answer

A

B. True

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

Question 7

Q

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

A

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

Q

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

A. Sampling rate conversion
B. Decimation
C. Interpolation

Answer

A

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

Q

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

A

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

Q

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

A

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

Q

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

Answer

A

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

Q

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

A

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

Q

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

A

B. FIR filters are not immune to noise.

FIR filters are highly immune to noise.

Question 14

Q

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

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

Answer

A

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

Q

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

A

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

Q

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

A

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

Q

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

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

Answer

A

A. real

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

Question 18

Q

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

A

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

The filters in the cascade realization are
connected in series.

Question 19

Q

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

A

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

Q

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

A

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

Q

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

A

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

Q

Musical instruments makes sounds
usually in what range?

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

Question 23

Q

Which of the following has an operation
bandwidth?

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

Answer

A

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

Q

Which of the following has the widest
bandwidth?

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

Answer

A

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

Q

Is that portion of the electromagnetic
spectrum occupied by a signal.

A. Power
B. Frequency
C. Wavelength
D. Bandwidth

Answer

A

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

Q

For a ____ channel, we need to use the Shannon capacity to find the maximum bit rate.

A. low-pass
B. noiseless
C. noisy

Question 27

Q

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

A

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

Q

Which of the following is classified as
Correlated noise?

A. flicker noise
B. harmonic distortion
C. shot noise
D. white noise

Answer

A

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

Q

Which of the following does not affect
shot noise current?

A. DC current
B. bandwidth
C. frequency
D. none of these choices

Answer

A

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

Q

Shot noise is a

A. Poisson process
B. None of these choices
C. Stochastic process

Answer

A

A. Poisson process

Question 31

Q

Shot noise is produced by

A. Protons
B. Electrons
C. Electrons & protons

Answer

A

C. Electrons & protons

Shot noise occurs due to particle like
the behaviour of electron and photon.

Question 32

Q

The value of resistor creating thermal
noise is doubled. The noise power
generated therefore

A. doubled
B. halved
C. quadrupled
D. unchanged

Answer

A

D. unchanged

Noise power is not dependent on
resistance.
Pn=KTB

Question 33

Q

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

A

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

Q

Burst noise affects FM systems.

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

Answer

A

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

Q

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

A

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

Q

Shot noise is avoidable when current is

A. Zero
B. Infinity
C. None of these choices
D. One

Answer

A

A. Zero

Shot noise is avoidable only when the
current is zero.

Question 37

Q

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

A

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

Q

A frequency that is an integer multiple
of the fundamental frequency.

A. fundamental frequency
B. harmonic frequency
C. 2nd harmonic
D. 3rd harmonic

Answer

A

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

Q

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

A

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

Q

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

A

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

Q

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

A

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

Q

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

A

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

Q

Single sideband AM systems occupy
same bandwidth as of conventional AM
systems.

A. Partly true
B. False
C. True

Answer

A

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

Q

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

A

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

Q

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

A

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

Q

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

A

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

Q

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

A

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

Q

FM bandwidth is approximated using ___ rule.

A. Carson’s
B. Faraday’s
C. Maxwell’s
D. Armstrong’s

Answer

A

A. Carson’s

Question 49

Q

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

A

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

Q

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

A

A. reduce the bandwidth used

The modulation process will increase
the bandwidth of the system.

Question 51

Q

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

A

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

Q

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

A

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

Q

FM uses class ___ amplifiers and AM
uses class ___ amplifiers.

A. AB, C
B. C, A
C. C, C
D. A, C

Answer

A

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

Q

Frequency multiplier multiplies the
frequency deviation produced by the
modulator.

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

Answer

A

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

Q

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

A

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

Q

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

A

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

Q

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

A

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

Q

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

A

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

Q

The components of TRF includes the
following, except:

A. Detector
B. AF Amplifier
C. Mixer

Answer

A

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

Q

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

A

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

Q

In superhet, which is considered as the
first detector?

A. Detector
B. RF Amplifier
C. Mixer
D. IF Section

Answer

A

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

Q

Frequency demodulator is a frequency
to amplitude converter circuit.

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

Answer

A

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

Q

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

A

B. single-frequency; composite

Question 64

Q

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

A

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.

Answer 63

A

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.

Answer 64

A

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

Answer 65

A

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.

Answer 66

A

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.

Answer 67

A

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.

Answer 68

A

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.

Answer 69

A

B. Increasing channel bandwidth &signal
power

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

Answer 70

A

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.

Answer 71

A

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.

Answer 72

A

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.

Answer 73

A

A. triggered

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

Answer 74

A

B. Increasing

SQNR can be improved by increasing
the sampling rate.

Answer 75

A

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.

Answer 76

A

A. VSB System

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

Answer 77

A

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.

Answer 78

A

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.

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