est_2019
What is the reflection coefficient for a transmission line with incident voltage of 4 V and reflected voltage 0.75 V?
0.1875
Voltage and current readings are taken on a transmission line at different points. The maximum voltage reading is 30 Vrms(max) and the minimum voltage reading is 10 Vrms(min). If the maximum current reading on the line is 1.5 A, what is the lowest current reading?
0.5 A
A dipole antenna using traps is designed to transmit a 140 MHz signal and a 90 MHz signal. What is the distance between trans given a velocity factor of 0.90?
0.965
The velocity of signal in air is 140 and becomes 100 as it passes through another medium. What is the index of refraction of the second medium?
1.4
A commonly used coaxial cable RG-8 A/U, has a capacitance of 29.5 pF/ft and inductance of 73.75 nH/ft, determine the amount of delay induced by a 1-ft section of this line if it will be used as a delay line
1.475 ns
Rainfaill is an important factor for fading of radio waves at frequencies above
10 GHz
Angle between an inverted V antenna is
105 degrees - 115 degrees
The number of voice channels in a basic FDM group is
12
A free space attenuation between two microwave antennas 40 km apart operating at 8 GHz is
142.55 dB
If the two towers of a 2 MHz antenna are separated by 120 electrical degrees, what is the tower separation in feet?
164 ft
The power gain of a half wave dipole with respect to an isotropic radiator
2.15 dB
A pulse requires 553 nanoseconds to travel from one end of a 111-meter coaxial cable to the other, what is the dielectric constant of the cable?
2.23
Which beamwidth represents the best antenna directivity?
20
The range of DC current that flows through a telephone is
20 mA to 80 mA
A super heterodyne receiver with an IF of 450 kHz is tuned to a signal at 1200 kHz. The image frequency is
2100 kHz
At what height must a satellite be placed above the surface of the earth in order for its rotation to be equal to the earth's rotation?
22,426.4 miles
What is the power gain in dB for an antenna with a directive gain of 30 dB and an efficiency of 75%?
28.75 dB
Radians per second is equal to
2pi * f
What is the frequency range of C band?
3.4 to 6.425 GHz
What frequency range do millimeter waves cover?
30 GHz - 300 GHz
At what angle is the direction of propagation in the XY plane if the E field is 180 degrees from the vertical?
45 deg
Given MUF as 7050 kHz, critical angle is 35 degrees, what is the critical frequency of this sky wave signal?
5775 MHz
What would be the physical size of a Hertz antenna operating at 97.1 MHz (k = 0.95)
58 inches
A paraboloid is to have power gain of 41.55 dB. If the frequency of operation is to be 8 GHz, what is the diameter of the parabolic reflector?
6 ft
The distance between adjacent nodes of a standing wave in air dielectric is determined to be 2.406 cm. What is the frequency of the generator?
6.23 GHz
The efficiency of an antenna is 82%. Its radiation resistance is 30 ohms. What is the value of its loss resistance?
6.58 ohms
If the carrier of a 100 percent modulated AM wave is suppressed, the percentage power saving will be
66.66
Two parallel wires placed 10 inches apart make use of wires having diameter of 81 mils. What is the characteristic impedance of the line?
660 ohms
A particular cable has a capacitance of 40 pF/ft and a characteristic impedance of 70 ohms. Determine the impedance of an infinitely long section of such cable.
70
A resonant half-wave dipole in free space has feed line current of 1 A. How much power appears at the input to the feed point?
73 W
What is the radiation resistance of a halfwave folded dipole in ohms?
75
What is the difference in amount of impedance between a three-wire dipole and a center-fed dipole?
9 times the feed point impedance
Indicate the correct statement regarding satellite communications
A satellite earth station must have as many receiver chains as there are carriers transmitted to it
To separate channels in a FDM receiver, it is necessary to use
AND gates
Which polarization can be reasonably well received by a circularly polarized antenna?
All of the above (vertical, circular, horizontal)
What is a trap antenna?
An antenna capable of being used on more than one band because of the presence of parallel LC networks
In a half-wave antenna, where are the current nodes?
At the ends
Mathematically, the calculation of FM bandwidth requires the use of
Bessel functions
What bond does VSAT first operate?
C-band
DTMF stands for
Dual-Tone Multifrequency
What is the layer of the ionosphere that is 255 km in height?
F2
A satellite beam that covers almost 42.5% of the earth's surface
Global beam
Indicate in which of the following only one sideband is transmitted
H3E
Which of the following is a wideband omni directional HF-UHF antenna?
Helical antenna
Hartley's Law is
I = ktB
Indicate the false statement
Impulse noised voltage is independent of the bandwidth
To increase the transmission distance of a UHF signal, which of the following should be done?
Increase antenna height
Indicate which one of the following is not an advantage of FM over AM
Lower bandwidth is required
What is the polarity of the currents that feed the V antenna?
Opposite
Indicate which of the following system is digital
Pulse Code Modulation
Which of the following is not an omnidirectional antenna?
Rhombic
The antenna separation (in meters) required for optimum operation of space diversity can be calculated from (where R is the effective earth radius (m) and L is path length (m))
S = 3*(lambda)*R / L
Collects very weak signals from broadcast satellite?
Satellite dish
Which of the reception problems below is not due to multipath?
Slow fading
The first satellite that transmits and receives simultaneously is called
Telstar 1
Indicate the false statement regarding the advantages of SSB over double sideband, full carrier AM
Transmitter circuits must be more stable. Giving better reception
Tropospheric scatter is used with frequencies in the following range
UHF
The equation for full-carrier AM is:
V(t) = (Ec+Em*sin(wmt))*sin(wct)
What type of polarization should be used if an antenna is mounted on a moving vehicle at frequencies below 50 MHz?
Vertical
Indicate the false statement. The SWR on a transmission line is infinity; the line is terminated in
a complex impedance
A pre-emphasis circuit provides extra noise immunity by
amplifying the high audio frequencies
For QAM, the two dimensions of its symbol space are
amplitude and phase angle
Interlacing is used in television to
avoid flicker
Microwave link repeaters are typically 50km apart
because of the earth's curvature
An example of an unbalanced line is
coaxial cable
When microwave signals follow the curvature of the earth, this is known as
ducting
Image frequencies occur when two signals:
enter the mixer, one below and one above the local oscillator by a difference equal to the IF
For best matching, the load on a cable should be
equal to Zo
Comparing the signal strength at the driven element from the desired direction to the signal strength reaching the driven element from the opposite direction
front to back ratio
How does the gain of a parabolic dish type antenna change when the operating frequency is doubled?
gain increases 6 dB
One of the main functions of the RF amplifier in a super heterodyne receiver is to
improve the rejection of the image frequency
As frequency increases, the resistance of a wire
increases
Time division multiplex
interleaves pulses belonging to different transmissions
Satellite engines use
ion propulsion system
The carrier is simultaneously modulated by two sine wave with the modulation indices of 0.3 and 0.4; the total modulation index
is 0.5
The effective length of a dipole is given by the formula
lambda / pi
Short circuited stubs are preferred to open circuited stub because the latter are
liable to radiate
Space waves are
line-of-sight
The Hartley Shannon theorems set a limit on the
maximum capacity of a channel with a given noise level
When two or more signals share a common channel, it is called
multiplexing
The radius of the circle you draw on a Smith Chart represents
none of the above (voltage, current, impedance)
The optimum value for SWR is
one
The cavity magnetron uses strapping to
prevent mode jumping
. Indicate which of the following reasons for using a counterpoise with antennas is false
protection of personnel working underneath
Indicate the false statement. Modulation is used to
reduce the bandwidth used
The end impedance of a half wave dipole is
resistive and high
The wavelength of a radio signal is
the distance a wave travels in one period
The Hartley law states that
the maximum rate of information transmission depends on the channel bandwidth
In the spectrum of a frequency modulated wave
the amplitude of any sideband depends on the modulation index
An FM receiver switching suddenly between two stations on nearby frequencies is called
the capture effect
The "attenuation of free space" is due to
the decrease in energy per square meter due to expansion of the wavefront
"Skin effect" refers to
the increase of wire resistance with frequency
The technology that made cellphones practical was
the microprocessor chip
The two basic specifications for a receiver are
the sensitivity and the selectivity
A directional coupler with three or more holes is sometimes used in preference to the two-hole coupler
to increase the bandwidth of the system
If k-factor is greater than 1, the array beam is bent
towards the earth
The main difference between the operation of transmission lines and wave guides is that
transmission lines use the principal mode of propagation and therefore do not suffer from low frequency cut off
Equalizing pulses in TV are sent during
vertical blanking
A positive voltage pulse sent down a transmission line terminated in a shortcircuit
would reflect as a negative pulse