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EST > REM A LVL 3 > Flashcards

REM A LVL 3 Flashcards

1
Q

Y(t)=×(2t) is a/an ___

A. Amplitude scaled signal by a factor of 2
B. Shifted signal
C. Compressed signal
D. Expanded signal

A

C. Compressed signal

By comparing the given equation with y(t)=x(at) we get a=2. If a> 1 the is compressed version x(t).

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2
Q

Y(t)= x(t/5) is a/an___.

A. Expanded signal
B. Amplitude scaled signal by factor 1/5
C. Time shifted signal
D. Narrow signal

A

A. Expanded signal

y(t)= x(at), comparing this with the
given expression we get a = 1/5. If 0 < a
< 1 the it is expanded (stretched)
version of x(t).

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3
Q

The operation is done by replacing the
independent variable n by -n.

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

A

A. Folding the signal

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4
Q

The method responsible for introducing
the aliasing effect in filters is

A. Impulse invariant and Bilinear
transformation method
B. Impulsive invariant method
C. None of these choices
D. Bilinear transformation method

A

B. Impulsive invariant method

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5
Q

Find the Nyquist rate for the signal f(t)=
rect(200t).

A. None of these choices
B. 0HZ
C. infinity HZ
D. 0 HZ

A

C. infinity HZ

Given f(t)= rect(200t), which is a
rectangular pulse signal having pulse
width of 1/200 seconds. Since the
signal is a finite duration signal, it is not
band-limited. The signal spectrum
consists of infinite frequencies. Hence,
Nyquist rate is infinity and Nyquist
interval is zero.

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6
Q

Which of the following technique is more preferable for design of linear phase FIR filter?

A. Window design
B. Chebyshev approximation
C. None of the mentioned
D. Frequency sampling

A

B. Chebyshev approximation

The chebyshev approximation method
provides total control of the filter
specifications, and as a consequence, it is usually preferable over the other two methods.

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7
Q

Which of the following filters cannot be
designed using impulse invariance
method?

A. Low pass
B. Low and band pass
C. High pass

A

C. High pass

It is clear that the impulse invariance
method is in -appropriate for designing
high pass filter due to the spectrum
aliasing that results from the sampling
process.

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8
Q

What is the equation for normalized
frequency?

A. F.Fs
B. Fs/F
C. F/Fs
D. None of the mentioned

A

C. F/Fs

In the impulse invariance method, the
normalized frequency f is given by
f= F/Fs.

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9
Q

Which of the filters have a frequency
response as shown in the figure below?

(REM A EST LVL3 FIGURE)

A. Digital filter without aliasing
B. Analog filter
C. None of the mentioned
D. Digital filter with aliasing

A

D. Digital filter with aliasing

In the given diagram, the continuous line
is the frequency response of analog
filter and dotted line is the frequency response of the corresponding digita filter with aliasing

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10
Q

The incorrect statement about the
impulse invariant method is

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

A

D. Absence of many-to-one mapping

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11
Q

In making dB computations, when the output power of an amplifier is 2 times the input power, the dB value is:

A. it can’t be determined
B. less than 0 dB
C. greater than 0 dB
D. it can’t be determined

A

C. greater than OdB

Gain or Loss Equation in dB:
dB=10log P_out/P_in
If the output is 2 times the input then
the ratio is 2:1.
dB=10log 2/1=3dB (a positive value/
greater than 0)
A ‘dB’ which is positive or greater than
‘O’ represents an output which is greater
than the input or a GAIN.
A’dB’ which is negative or lesser than’0’
represents an output which is lesser
than the input or a LOSS
A’dB’ which is zero ‘0’ represents an
output which is equal to the input.

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12
Q

It is used to express the ratio of one value of a power or field quantity to another.

A. log
B. decibel
C. none of these choices

A

B. decibel

The decibel (dB) is a relative unit of
measurement equal to 1/10 of a bel. It is used to express the ratio of one value of a power or quantity to another. It can also be used to express a change in
value or an absolute value. As an
absolute value, it is used to represent the ratio of a value to a fixed reference value in which the suffix indicates the reference value. dB(suffix)

Ex:
If the reference power is 1W, then the
unit becomes dBW, W is the suffix.
If the reference power is 1mW, then the
unit becomes dBm, m is the suffix.
If the reference power is 1uW, then the
unit becomes dBu, u is the suffix.

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13
Q

When the reference power is 1mW, the
dB unit becomes:

A. dBu
B. dBW
C. dB
D. dBm

A

D. dBm

When 2 powers are taken as a ratio
without a reference power, a dB unit can be used. When 2 powers are taken as a ratio and has a reference power, the unit dB(suffix) is used and the suffix
indicates the reference value.

Example:
If there is no reference power, simply
use dB unit.
If the reference power is 1W, then the
unit becomes dBW.
If the reference power is 1mW, then the
unit becomes dBm.
If the reference power is 1uW, then the
unit becomes dBu.
If the reference power is 1nW, then the
unit becomes dBn.

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14
Q

Where is the noise generated which
primarily determines the signal-to-noise
ratio in a VHF (150 MHz) marine band
receiver?

A. Man-made noise
B. In the atmosphere
C. In the ionosphere
D. In the receiver front end

A

D. In the receiver front end

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15
Q

You are transmitting FM on the 2 metre band. Several stations advise you that your transmission is distorted. A quick check with a frequency counter tells you that the transmitter is on the proper
frequency. Which of the following is the
most probable cause of the distortion?

A. The repeater is reversing your sidebands
B. The frequency deviation of your
transmitter is set too high
C. The power supply output voltage is low
D. The frequency counter is giving an
incorrect reading and you are indeed off
frequency

A

B. The frequency deviation of your
transmitter is set too high

DISTORTION.’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’).

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16
Q

What may happen if an SSB transmitter
is operated with the microphone gain
set too high?

A. It may cause digital interference to
computer equipment
B. It may cause interference to other stations
operating on a higher frequency band
C. It may cause splatter interference to
other stations operating near its
frequency
D. It may cause atmospheric interference in
the air around the antenna

A

D. It may cause atmospheric interference in
the air around the antenna

MICROPHONE GAIN SET TOO HIGH.
This leads to ‘overmodulation’
evidenced by distorted speech plus
using excessive bandwidth on the air
(splatter) which interferes with stations
using adjacent frequencies (‘out-of-
channel emissions’).

17
Q

When selecting a single-sideband phone
transmitting frequency, what minimum
frequency separation from a contact in
progress should you allow (between
suppressed carriers) to minimize
interference?

A. Approximately 3 kHz
B. Approximately 10 kHz
C. Approximately 6 kHz
D. 150 to 500 Hz

A

A. Approximately 3 kHz

In order of bandwidth requirements: CW
= about 100 Hz, RTTY = about 600 Hz,
SSB= 2 to 3 kHz, FM= 10 to 20 kHz.Minimum frequency separation: CW =150 to 500 Hz,RTTY=250 to 500 Hz,SSB=3 kHz to 5kHz.

18
Q

It is also known as center-tapped or
phase discriminator.

A. Ratio Detector
B. Slope Detector
C. Foster-Seeley Detector
D. Phase Locked Loop

A

C. Foster-Seeley Detector

Foster-Seeley Discriminator - changes in
the magnitude of the input signal will
give rise to the amplitude changes in
the resulting output voltage. Also known
as the center tapped or phase
discriminator.

19
Q

What is one way to shorten transmitter tune-up time on the air to cut down on interference?

A. Use a random wire antenna
B. Use twin lead instead of coaxial cable feed
lines
C. Tune up on 40 metres first, then switch to
the desired band
D. Tune the transmitter into a dummy load

A

D. Tune the transmitter into a dummy load

The ‘Dummy Load’ (a resistor with a
high power rating) dissipates RF energy as heat without radiating the RF on the air. Permits tests or adjustments
without causing interference to other
stations. The ‘tuning process’ (or
oading’) refers to a manual procedure necessary for equipment with vacuum tube final Power Amplifiers where variable capacitors needed to be adjusted.

20
Q

At the CRC generator, ______
added to the data unit after the division process

A. 0s are
B. The CRC remainder is
C. The polynomial is
D. 0s are

A

B. The CRC remainder is

21
Q

Which of the following is the ratio of the
throughput data rate per Hertz?

A. Power efficiency
B. Spectral density
C. Power density
D. Bandwidth efficiency

A

D. Bandwidth efficiency

Bandwidth efficiency reflects how
efficiently the allocated bandwidth is
utilized. It is defined as the ratio of
throughput data rate per Hertz in a given
bandwidth. It describes the ability of a
modulation scheme to accommodate
data within a limited bandwidth.

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 favourably the trade-off between fidelity and signal power is made.

22
Q

Which pulse modulation technique is
least expensive?

A. Pulse width modulation
B. Pulse amplitude modulation
C. Pulse position modulation
D. Pulse code modulation

A

B. Pulse amplitude modulation

Out of all the pulse modulation
techniques, Pulse amplitude modulation
is the least expensive and simplest to
implement. In pulse amplitude
modulation, the amplitude of the pulse
varies with the amplitude of the
modulating signal.

23
Q

Trunks are transmission media such as
the handle the telephone
communication between offices.

A. Twisted-pair cable
B. Fiber-optic and Satellite links
C. Satellite links
D. Fiber-optic cable

A

B. Fiber-optic and Satellite links

24
Q

Which of the following is true for a
Gaussian filter?

A. Sharp cut off
B. Large bandwidth
C. High overshoot
D. Low overshoot

A

A. Sharp cut off

The Gaussian filter has a narrow
absolute bandwidth, and has a sharp cut off, low overshoot and pulse area preservation properties. This makes it attractive for use in mobile communication that uses nonlinear RF
amplifiers.

EST (10 decks)

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