問題一覧
1
Amplitude Modulation suffers from ________
Cross Modulation
2
The ability of receivers to select the wanted signals among various incoming signal is called ________
Selectivity
3
In TV transmission, picture signal is ________ modulated.
VSB
4
The analog signal needs to be sampled at a minimum sampling rate of:
2fs
5
If the height of the reflecting layer of the ionosphere increases, the skip distance of a high frequency (HF) transmission:
becomes greater
6
Radio waves that arrive at a receiving site along different paths can cause signal fading if these waves have different _____.
phase relationships
7
In a frequency modulation receiver, the _______ is located between the limiter and the audio frequency amplifier.
frequency discriminator
8
What does horizontal wave polarization mean?
The electric lines of force of a radio wave are parallel to the earth`s surface
9
In digital transmission, what modulation technique requires minimum bandwidth?
Delta modulation
10
The error probability of a PCM is:
All of the choices
11
What kind of emission would your FM transmitter produce if its microphone failed to work?
An unmodulated carrier
12
In a low-level AM system, amplifiers following the modulated stage must be:
linear devices
13
How little electrical current flowing through the human body can be fatal?
As little as 20 milliamperes
14
Reception of high frequency (HF) radio waves beyond 4000 km is generally possible by _____ wave.
ionospheric
15
What may happen if an SSB transmitter is operated with the microphone gain set too high?
It may cause splatter interference to other stations operating near its frequency
16
Consider the same noiseless channel of 3000 Hz bandwidth transmitting a signal with four signal levels (for each level, we send 2 bits). Calculate the maximum bit rate.
12 kbps
17
A digital signal has eight levels. How many bits are needed per level?
3
18
A one-to-all communication between one source and all hosts on a network is classified as a _______ communication.
broadcast
19
We have a low-pass channel with bandwidth 100 kHz. What is the maximum bit rate of this channel?
200 kbps
20
A router is a connecting device that operates in the _______ layer(s).
physical, data-link, and network
21
A network with bandwidth of 10 Mbps can pass only an average of 12,000 frames per minute with each frame carrying an average of 10,000 bits. What is the throughput of this network?
2 Mbps
22
Which of the following restrictions apply to analog broadcasting?
Interference, fading and multipath reception
23
When propagation speed is multiplied by propagation time, we get the ________.
distance a signal or bit has traveled
24
Assume that we need to download text documents at the rate of 100 pages per minute. A page is an average of 24 lines with 80 characters in each line and each character requires 8 bits. Then the required bit rate of the channel is _____.
25.6 kbps
25
What factor significantly affects the frequency of occurrence of the sporadic-E layer?
Latitude
26
We need to send 265 kbps over a noiseless channel with a bandwidth of 20 kHz. How many signal levels do we need?
98.7 levels
27
A signal travels through an amplifier, and its power is increased 10 times. Calculate the amplification or gain of power.
10 dB
28
If we transmit a signal, the frequency of which is so high we no longer receive a reflection from the ionosphere, the signal frequency is above the:
maximum usable frequency
29
The signal-to-noise ratio is often given in decibels. Assume that SNR = 36 dB and the channel bandwidth is 2 MHz. Calculate the theoretical channel capacity.
24 Mbps
30
Consider an extremely noisy channel in which the value of the signal-to-noise ratio is almost zero. In other words, the noise is so strong that the signal is faint. Calculate the channel capacity.
0
31
The power of a signal is 10 mW and the power of the noise is 1 µW. What are the values of SNR and SNR_dB?
40 dB
32
Consider a noiseless channel with a bandwidth of 3000 Hz, transmitting a signal with two signal levels. What is the maximum bit rate?
6 kbps
33
If link transmits 4000 frames per second and each slot has 8 bits, the transmission rate of circuit of this TDM is ______.
32 kbps
34
The greatest amount of absorption takes place in the ionosphere under which of the following conditions?
When the density of the ionized layer is the greatest.
35
Two or more strong out-of-band signals mix in your receiver to produce interference on a desired frequency. What is this called?
Intermodulation interference
36
Radio communications can be diffracted to exceptionally long distances through the use of what frequency band at what relative power level?
Very low frequency; High power
37
Radio waves above the MUF will experience what effect when refracted from the ionosphere?
They will overshoot the desired location
38
The effectiveness of a data communications system depends on what four fundamental characteristics?
Delivery, accuracy, timeliness, and jitter
39
A parity-check code can detect an ____ number of errors.
odd
40
What is the process of adding one extra byte whenever there is a flag or escape character in the text?
Byte stuffing
41
For transmission over bodies of water, _______ polarization is much better for antennas at the lower heights.
vertical
42
In the reflection of waves, if the reflecting surface is smooth and polished, the angle between the incident ray and the normal will be ______ the angle between the reflected ray and the normal.
the same as
43
What is the most common UTP connector, which is a keyed connector, meaning the connector can be inserted in only one way?
RJ45
44
Substances that transmit almost all the light waves that fall upon them are said to be ______.
transparent
45
What signals can be used for short-range communication in a closed area using line-of-sight propagation?
Infrared
46
The first service provided by the data-link layer is ______.
framing
47
In ____ propagation, higher-frequency radio waves radiate upward into the ionosphere (the layer of atmosphere where particles exist as ions) where they are reflected back to earth.
sky
48
In _____ TDM, the data rate of the link is n times faster, and the unit duration is n times shorter.
synchronous
49
In wave propagation, the reflected energy is the greatest when the wave is _____ to the reflecting surface.
nearly parallel
50
Consider the same noiseless channel of 3000 Hz bandwidth transmitting a signal with four signal levels (for each level, we send 2 bits). Calculate the maximum bit rate.
12 kbps
51
The _____ ray passes through the axis of the fiber core.Select one:
Meridional
52
On which of the following signals does PLC operate on?
Digital
53
A traveling-wave tube (TWT) amplifies by virtue of
The absorption of energy by the signal from an electron stream
54
Why is a Yagi antenna often used for radio communications on the 20-metre band?
It helps reduce interference from other stations off to the side or behind
55
Ducts shall be supported with approved hangers at intervals not exceeding feet.
10
56
Which one is a causal system?
y(n) = 3x[n] - 2x[n - 1]
57
The spacing between the elements on a three-element Yagi antenna, representing the best overall choice, is _______ of a wavelength.
0.2
58
All causal systems must have the component of
Memory
59
Calculate the effective earth's radius if the surface refractivity is 301.
8493 km
60
A single mode fiber has refractive indices n1=1.50, n2 = 2.23, core diameter of 8μm, wavelength = 1.5μm cutoff wavelength = 1.214μm. Find the radius of curvature?
34 mm
61
The "doublet antenna" is the most common in the amateur service. If you were to cut this antenna for 3.75 MHz, what would be its approximate length?
38 meters (125 ft.)
62
What is the minimum spectrum allocation required by W-CDMA?
5 MHz
63
A system is said to be defined as non-causal, when
The output at the present depends on the input at time instant in the future.
64
A loss less line of characteristic impedance Z0 is terminated in pure reactance of -jZ0 value. VSWR is
infinity
65
Directors are used to increase ______ of the Yagi-Uda antenna.
Gain
66
Microwave frequencies are normally regarded as those in the range of
10 to 1000 GHz
67
The signal defined by the equations f(t) = 0 for t < 0, f(t) = E for 0 ≤ t ≤ a and f(t) = 0 for t > a is
a pulse function
68
A polarization maintaining fiber operates at a wavelength 1.2μm and have a modal birefringence of 1.8*10-3. Calculate the period of perturbation.
0.6 seconds
69
A magnetron is operated at a duty cycle of 0.001. It has a peak power output of 100 kilo-watts. Its average power is
100 watts
70
Effective noise temperature Te in terms of noise figure is ____
Te=To (F-1)
71
What kind of antenna feed line is made of two conductors held apart by insulated rods?
Open-conductor ladder line
72
A signal g(t) = A then g(t) is a
power signal
73
In a single-phase half-wave thyristor with R load and Vs = Vmsin(wt), the maximum value of the load can be given by
Vm/2
74
How much heat is produced by a human body?
100 W
75
A single mode fiber has mode field diameter 10.2μm and V = 2.20. What is the core diameter of this fiber?
10.1μm
76
Which of the following feeding has largest bandwidth?
Proximity Coupling
77
Assertion (A): If the duty cycle of chopper is low the current would not become discontinuous.
Reason (R): If the time constant L/R of the load in chopper is low the current may become discontinuous.
A is correct but R is wrong
78
A single phase semiconverter is feeding a highly inductive load and has freewheeling diode across the load. The waveshapes of output voltage and output current.
are not similar
79
In a single phase full wave converter (M - 2 connection) feeding a highly inductive load, the firing angle for each thyristor is a in the respective half cycle. The period of conduction of each thyristor is
pI
80
An energy signal has G(f) = 10. Its energy density spectrum is
100
81
A class A chopper has an input voltage of 200 V. Ton = 1.5 ms, and Toff = 4.5 ms. The duty cycle, average output voltage and ripple factor, respectively, are
0.25, 50 V and sqrt(3)
82
Coupling into and out of a traveling-wave tube can be accompanied by a
All of the above
83
In a frequency modulation transmitter, the _______ is located between the modulator and the frequency multiplier.
oscillator
84
A single phase full controlled bridge converter is connected to load having R = 0.4 £, E = 120 V, L = 0.2 mH, Vs = 230 V. The RMS value of the load current is 10 A for a firing angle of 53.21°. Find the input power factor.
0.5391 lag
85
Two thyristor of same rating and same specifications
may have equal or unequal turn on and turn off periods
86
What is one disadvantage of EDGE in comparison to HSCSD and GPRS?
Small coverage range
87
What is the low angle radiation pattern of an ideal half-wavelength dipole HF antenna installed parallel to the earth?
It is a figure-eight, perpendicular to the antenna
88
Which one of the following systems is causal?
y(t) = x(t-1) + x(t−2)
89
In a frequency modulation transmitter, the input to the speech amplifier is connected to the:
microphone
90
Klystron oscillators are most often used in the frequency range of
3000 to 30000 MHz
91
If the input power 100μW is launched into 6 km of fiber, the mean optical power at the fiber output is 2μW. What is the overall signal attenuation through the fiber assuming there are no connectors or splices?
16.98dB
92
What is the full form of MIDAS with respect to data acquisition package?
Maximum integrated data acquisition system
93
If k-factor is greater than 1, the array beam is bent
Towards the earth
94
The maximum usable range of the usual radar set (on any particular range setting) is determined by
The interval between transmitted pulses
95
How many directly driven elements do most Yagi antennas have?
One
96
In Laplace transform, multiplication by e-at in time domain becomes
translation by a in s domain
97
Which of the following is used to excite the antenna?
Feed line
98
Which conversion takes place when music is played from a memory card?
DAC
99
What should be the noise figure value at which the effective noise temperature equals to room temperature?
2
100
What type of interface does a DAQ (Data Acquisition) hardware creates?
Interface between a computer and signal
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50問 • 1年前問題一覧
1
Amplitude Modulation suffers from ________
Cross Modulation
2
The ability of receivers to select the wanted signals among various incoming signal is called ________
Selectivity
3
In TV transmission, picture signal is ________ modulated.
VSB
4
The analog signal needs to be sampled at a minimum sampling rate of:
2fs
5
If the height of the reflecting layer of the ionosphere increases, the skip distance of a high frequency (HF) transmission:
becomes greater
6
Radio waves that arrive at a receiving site along different paths can cause signal fading if these waves have different _____.
phase relationships
7
In a frequency modulation receiver, the _______ is located between the limiter and the audio frequency amplifier.
frequency discriminator
8
What does horizontal wave polarization mean?
The electric lines of force of a radio wave are parallel to the earth`s surface
9
In digital transmission, what modulation technique requires minimum bandwidth?
Delta modulation
10
The error probability of a PCM is:
All of the choices
11
What kind of emission would your FM transmitter produce if its microphone failed to work?
An unmodulated carrier
12
In a low-level AM system, amplifiers following the modulated stage must be:
linear devices
13
How little electrical current flowing through the human body can be fatal?
As little as 20 milliamperes
14
Reception of high frequency (HF) radio waves beyond 4000 km is generally possible by _____ wave.
ionospheric
15
What may happen if an SSB transmitter is operated with the microphone gain set too high?
It may cause splatter interference to other stations operating near its frequency
16
Consider the same noiseless channel of 3000 Hz bandwidth transmitting a signal with four signal levels (for each level, we send 2 bits). Calculate the maximum bit rate.
12 kbps
17
A digital signal has eight levels. How many bits are needed per level?
3
18
A one-to-all communication between one source and all hosts on a network is classified as a _______ communication.
broadcast
19
We have a low-pass channel with bandwidth 100 kHz. What is the maximum bit rate of this channel?
200 kbps
20
A router is a connecting device that operates in the _______ layer(s).
physical, data-link, and network
21
A network with bandwidth of 10 Mbps can pass only an average of 12,000 frames per minute with each frame carrying an average of 10,000 bits. What is the throughput of this network?
2 Mbps
22
Which of the following restrictions apply to analog broadcasting?
Interference, fading and multipath reception
23
When propagation speed is multiplied by propagation time, we get the ________.
distance a signal or bit has traveled
24
Assume that we need to download text documents at the rate of 100 pages per minute. A page is an average of 24 lines with 80 characters in each line and each character requires 8 bits. Then the required bit rate of the channel is _____.
25.6 kbps
25
What factor significantly affects the frequency of occurrence of the sporadic-E layer?
Latitude
26
We need to send 265 kbps over a noiseless channel with a bandwidth of 20 kHz. How many signal levels do we need?
98.7 levels
27
A signal travels through an amplifier, and its power is increased 10 times. Calculate the amplification or gain of power.
10 dB
28
If we transmit a signal, the frequency of which is so high we no longer receive a reflection from the ionosphere, the signal frequency is above the:
maximum usable frequency
29
The signal-to-noise ratio is often given in decibels. Assume that SNR = 36 dB and the channel bandwidth is 2 MHz. Calculate the theoretical channel capacity.
24 Mbps
30
Consider an extremely noisy channel in which the value of the signal-to-noise ratio is almost zero. In other words, the noise is so strong that the signal is faint. Calculate the channel capacity.
0
31
The power of a signal is 10 mW and the power of the noise is 1 µW. What are the values of SNR and SNR_dB?
40 dB
32
Consider a noiseless channel with a bandwidth of 3000 Hz, transmitting a signal with two signal levels. What is the maximum bit rate?
6 kbps
33
If link transmits 4000 frames per second and each slot has 8 bits, the transmission rate of circuit of this TDM is ______.
32 kbps
34
The greatest amount of absorption takes place in the ionosphere under which of the following conditions?
When the density of the ionized layer is the greatest.
35
Two or more strong out-of-band signals mix in your receiver to produce interference on a desired frequency. What is this called?
Intermodulation interference
36
Radio communications can be diffracted to exceptionally long distances through the use of what frequency band at what relative power level?
Very low frequency; High power
37
Radio waves above the MUF will experience what effect when refracted from the ionosphere?
They will overshoot the desired location
38
The effectiveness of a data communications system depends on what four fundamental characteristics?
Delivery, accuracy, timeliness, and jitter
39
A parity-check code can detect an ____ number of errors.
odd
40
What is the process of adding one extra byte whenever there is a flag or escape character in the text?
Byte stuffing
41
For transmission over bodies of water, _______ polarization is much better for antennas at the lower heights.
vertical
42
In the reflection of waves, if the reflecting surface is smooth and polished, the angle between the incident ray and the normal will be ______ the angle between the reflected ray and the normal.
the same as
43
What is the most common UTP connector, which is a keyed connector, meaning the connector can be inserted in only one way?
RJ45
44
Substances that transmit almost all the light waves that fall upon them are said to be ______.
transparent
45
What signals can be used for short-range communication in a closed area using line-of-sight propagation?
Infrared
46
The first service provided by the data-link layer is ______.
framing
47
In ____ propagation, higher-frequency radio waves radiate upward into the ionosphere (the layer of atmosphere where particles exist as ions) where they are reflected back to earth.
sky
48
In _____ TDM, the data rate of the link is n times faster, and the unit duration is n times shorter.
synchronous
49
In wave propagation, the reflected energy is the greatest when the wave is _____ to the reflecting surface.
nearly parallel
50
Consider the same noiseless channel of 3000 Hz bandwidth transmitting a signal with four signal levels (for each level, we send 2 bits). Calculate the maximum bit rate.
12 kbps
51
The _____ ray passes through the axis of the fiber core.Select one:
Meridional
52
On which of the following signals does PLC operate on?
Digital
53
A traveling-wave tube (TWT) amplifies by virtue of
The absorption of energy by the signal from an electron stream
54
Why is a Yagi antenna often used for radio communications on the 20-metre band?
It helps reduce interference from other stations off to the side or behind
55
Ducts shall be supported with approved hangers at intervals not exceeding feet.
10
56
Which one is a causal system?
y(n) = 3x[n] - 2x[n - 1]
57
The spacing between the elements on a three-element Yagi antenna, representing the best overall choice, is _______ of a wavelength.
0.2
58
All causal systems must have the component of
Memory
59
Calculate the effective earth's radius if the surface refractivity is 301.
8493 km
60
A single mode fiber has refractive indices n1=1.50, n2 = 2.23, core diameter of 8μm, wavelength = 1.5μm cutoff wavelength = 1.214μm. Find the radius of curvature?
34 mm
61
The "doublet antenna" is the most common in the amateur service. If you were to cut this antenna for 3.75 MHz, what would be its approximate length?
38 meters (125 ft.)
62
What is the minimum spectrum allocation required by W-CDMA?
5 MHz
63
A system is said to be defined as non-causal, when
The output at the present depends on the input at time instant in the future.
64
A loss less line of characteristic impedance Z0 is terminated in pure reactance of -jZ0 value. VSWR is
infinity
65
Directors are used to increase ______ of the Yagi-Uda antenna.
Gain
66
Microwave frequencies are normally regarded as those in the range of
10 to 1000 GHz
67
The signal defined by the equations f(t) = 0 for t < 0, f(t) = E for 0 ≤ t ≤ a and f(t) = 0 for t > a is
a pulse function
68
A polarization maintaining fiber operates at a wavelength 1.2μm and have a modal birefringence of 1.8*10-3. Calculate the period of perturbation.
0.6 seconds
69
A magnetron is operated at a duty cycle of 0.001. It has a peak power output of 100 kilo-watts. Its average power is
100 watts
70
Effective noise temperature Te in terms of noise figure is ____
Te=To (F-1)
71
What kind of antenna feed line is made of two conductors held apart by insulated rods?
Open-conductor ladder line
72
A signal g(t) = A then g(t) is a
power signal
73
In a single-phase half-wave thyristor with R load and Vs = Vmsin(wt), the maximum value of the load can be given by
Vm/2
74
How much heat is produced by a human body?
100 W
75
A single mode fiber has mode field diameter 10.2μm and V = 2.20. What is the core diameter of this fiber?
10.1μm
76
Which of the following feeding has largest bandwidth?
Proximity Coupling
77
Assertion (A): If the duty cycle of chopper is low the current would not become discontinuous.
Reason (R): If the time constant L/R of the load in chopper is low the current may become discontinuous.
A is correct but R is wrong
78
A single phase semiconverter is feeding a highly inductive load and has freewheeling diode across the load. The waveshapes of output voltage and output current.
are not similar
79
In a single phase full wave converter (M - 2 connection) feeding a highly inductive load, the firing angle for each thyristor is a in the respective half cycle. The period of conduction of each thyristor is
pI
80
An energy signal has G(f) = 10. Its energy density spectrum is
100
81
A class A chopper has an input voltage of 200 V. Ton = 1.5 ms, and Toff = 4.5 ms. The duty cycle, average output voltage and ripple factor, respectively, are
0.25, 50 V and sqrt(3)
82
Coupling into and out of a traveling-wave tube can be accompanied by a
All of the above
83
In a frequency modulation transmitter, the _______ is located between the modulator and the frequency multiplier.
oscillator
84
A single phase full controlled bridge converter is connected to load having R = 0.4 £, E = 120 V, L = 0.2 mH, Vs = 230 V. The RMS value of the load current is 10 A for a firing angle of 53.21°. Find the input power factor.
0.5391 lag
85
Two thyristor of same rating and same specifications
may have equal or unequal turn on and turn off periods
86
What is one disadvantage of EDGE in comparison to HSCSD and GPRS?
Small coverage range
87
What is the low angle radiation pattern of an ideal half-wavelength dipole HF antenna installed parallel to the earth?
It is a figure-eight, perpendicular to the antenna
88
Which one of the following systems is causal?
y(t) = x(t-1) + x(t−2)
89
In a frequency modulation transmitter, the input to the speech amplifier is connected to the:
microphone
90
Klystron oscillators are most often used in the frequency range of
3000 to 30000 MHz
91
If the input power 100μW is launched into 6 km of fiber, the mean optical power at the fiber output is 2μW. What is the overall signal attenuation through the fiber assuming there are no connectors or splices?
16.98dB
92
What is the full form of MIDAS with respect to data acquisition package?
Maximum integrated data acquisition system
93
If k-factor is greater than 1, the array beam is bent
Towards the earth
94
The maximum usable range of the usual radar set (on any particular range setting) is determined by
The interval between transmitted pulses
95
How many directly driven elements do most Yagi antennas have?
One
96
In Laplace transform, multiplication by e-at in time domain becomes
translation by a in s domain
97
Which of the following is used to excite the antenna?
Feed line
98
Which conversion takes place when music is played from a memory card?
DAC
99
What should be the noise figure value at which the effective noise temperature equals to room temperature?
2
100
What type of interface does a DAQ (Data Acquisition) hardware creates?
Interface between a computer and signal