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WorksheetsEST 1
Total questions: 50
Worksheet time: 32mins
What is the refractive index of an ionospheric layer with 100 x 10^5 free electrons per m^3? Assume frequency to be at 20 MHz.
0.99
0.15
0.78
0.85
“Each point on a spherical wavefront may be considered a source of secondary spherical wavefronts”. This is known as the
Snell’s law
D’Alembert’s principle
Appleton’s theory
Huygen’s principle
What is meant by the term deviation ratio?
The ratio of the audio modulating frequency to the center carrier frequency.
The ratio of the maximum carrier frequency deviation to the highest audio modulating frequency.
The ratio of the carrier center frequency to the audio modulating frequency.
The ratio of the highest audio modulating frequency to the average audio modulating frequency.
What is the major cause of selective fading?
Small changes in the beam heading at the receiving station.
Large changes in the height of the ionosphere, as experience at the receiving station.
Time differences between the receiving and transmitting stations.
Phase differences between radio wave components of the same transmission, as experienced at the receiving station.
What phenomenon causes the radio-path horizon distance to exceed the geometric horizon?
E-layer skip.
D-layer skip.
Auroral skip.
Radio waves may be bent.
What propagation condition is usually indicated when a VHF signal is received from a station over 500 miles away?
D-layer absorption
Faraday rotation
Tropospheric ducting
Moonbounce
What is meant by the term modulation index?
The processor index.
The ratio between the deviation of a frequency modulated signal and the modulating frequency.
The FM signal-to-noise ratio.
The ratio of the maximum carrier frequency deviation to the highest audio modulating frequency.
The bending of radio waves passing over the top of a mountain range that disperses a weak portion of the signal behind the mountain is
eddy-current phase effect
knife-edge diffraction
shadowing
mirror refraction effect
What is the wavelength of a signal at 500 MHz?
0.062 cm
6 meters
60 cm
60 meters
What is included in the total resistance of an antenna system?
Radiation resistance plus space impedance
Radiation resistance plus transmission resistance
Transmission line resistance plus radiation resistance
Radiation resistance plus ohmic resistance
What are electromagnetic waves?
Alternating currents in the core of an electromagnet
A wave consisting of two electric fields at right angles to each other
A wave consisting of an electric field and a magnetic field at right angles to each other
A wave consisting of two magnetic fields at right angles to each other
The band of frequencies least susceptible to atmospheric noise and interference is:
30 – 300 kHz
300 – 3000 kHz
3 – 30 MHz
300 – 3000 MHz
What is the relationship in degrees of the electrostatic and electromagnetic fields of an antenna?
0 degree
45 degrees
90 degrees
180 degrees
For a space wave transmission, the radio horizon distance of a transmitting antenna with a height of 100 meters is approximately:
10 km
40 km
100 km
400 km
What is meant by referring to electromagnetic waves as horizontally polarized?
The electric field is parallel to the earth.
The magnetic field is parallel to the earth.
Both the electric and magnetic fields are horizontal
Both the electric and magnetic fields are vertical
What is meant by referring to electromagnetic waves as having circular polarization?
The electric field is bent into a circular shape.
The electric field rotates
The electromagnetic wave continues to circle the earth
The electromagnetic wave has been generated by a quad antenna
If a transmitting antenna is 100 meters high and a separate receiving antenna is 64 meters high, what is the maximum space wave communication distance possible between them?
18 km
72 km
164 km
656 km
A receiver is located 64 km from a space wave transmitting antenna that is 100 meters high. Find the required height of the receiving antenna.
36 meters high
64 meters high
100 meters high
182.25 meters high
Which of the following is not one of the natural ways a radio wave may travel from transmitter to receiver?
Ground wave
Microwave
Sky wave
Space wave
Which of the following terrain types permits a ground wave to travel the farthest?
Salt water
Fresh water
Sandy
Rocky
What is the input terminal impedance at the center if a folded dipole antenna?
300 ohms
72 ohms
50 ohms
450 ohms
What is the term used to describe a spread spectrum communications system where the center frequency if a conventional carrier is altered many time per second in accordance with a pseudo-random list of channels?
Frequency hopping
Direct sequence
Time-domain frequency modulation
Frequency compandored spread spectrum
What is the velocity factor for non-foam dielectric 50 or 75 ohm flexible coaxial cable such as RG 8, 11, 58 and 59?
2.70
0.66
0.30
0.10
If a transmission line has a power loss of 6 dB per 100 feet, what is the power at the feed point to the antenna at the end of a 200 foot transmission line fed by a 100 watt transmitter?
70 watts
50 watts
25 watts
6 watts
What determines the velocity factor in a transmission line?
he termination impedance
The line length
Dielectrics in the line
The center conductor resistivity
What term is used to describe a spread spectrum communications system in which a very fast binary bit stream is used to shift the phase of an RF carrier?
Frequency hopping
Direct sequence
Binary phase-shift keying
Phase compandored spread spectrum
Which of the following frequency bands is best suited for ground wave propagation?
30 to 300 kHz
300 kHz to 3 MHz
3 MHz to 30 MHz
30 MHz to 300 MHz
Which of the following frequency bands is best suited for sky wave propagation?
30 to 300 kHz
3 MHz to 30 MHz
30 MHz to 300 MHz
3 GHz to 30 GHz
What is the seventh harmonic of a 100 MHz quarter wavelength antenna?
14.28 MHz
107 MHz
149 MHz
700 MHz
Which if the following layers of the ionosphere has no effect on sky wave propagation during the hours of darkness?
D
E
F1
F2
Skip distance can be maximized by using the ____ radiation angle possible and the ____ frequency that will be refracted at that angle.
lowest, lowest
lowest, highest
highest, lowest
highest, highest
What is the meaning of the term “velocity factor” of a transmission line?
The ratio of the characteristic impedance of the line to the terminating impedance
The index of shielding for coaxial cable.
The velocity of the wave on the transmission line multiplied by the velocity of light in a vacuum.
The velocity of the wave on the transmission line divided by the velocity of light in a vacuum.
What is the term for the ratio of actual velocity at which a signal travels through a line to the speed of light in a vacuum?
Velocity factor
Characteristic impedance
Surge impedance
Standing wave ratio
Why is the physical length of a coaxial cable transmission line shorter than its electrical length?
Skin effect is less pronounced in the coaxial cable
RF energy moves slower along the coaxial cable
The surge impedance is higher in the parallel feed line
The characteristic impedance is higher in the parallel feed line
What would be the physical length of a typical coaxial transmission line that is electrically one-quarter wavelength long at 14.1 MHz?
20 meters
3.51 meters
2.33 meters
0.25 meter
To obtain the most reliable sky wave propagation the ____ should be used.
Lowest useable frequency (LUF).
Maximum useable frequency (MUF).
Optimum useable frequency (OUF).
Critical frequency
What is the deviation ratio for an FM-phone signal having a maximum frequency swing of plus or minus 5 kHz and accepting a maximum modulation rate of 3kHz?
60
0.16
0.6
1.66
Tropospheric scatter is a method of sky wave propagation for which of the following frequency bands?
300 kHz to 3 MHz
3 MHz to 30 MHz
30 MHz to 300 MHz
300 MHz to 3 GHz
What is the frequency range of an aircraft’s radio altimeter?
962 MHz to 1213 MHz
329.15 MHz to 335.00 MHz
4250 MHz to 4350 MHz
108.00 MHz to 117.95 MHz
What type of transmission is radiated from an aircraft’s radio altimeter antenna?
An amplitude modulated continuous wave
A pulse position modulated UHF signal
A differential phase shift keyed UHF signal
A frequency modulated continuous wave
The polarization of a radio wave:
Is perpendicular to the electrostatic field of the antenna
Is the same direction as the electrostatic field of the antenna.
Is the same direction as the magnetic field of the antenna.
Is perpendicular to both the electrostatic and magnetic fields of the antenna.
A coaxial cable has 7dB of reflected power when the input is 5 watts. What is the output of the transmission line?
5 watts
2.5 watts
1.25 watts
1 watt
When is it useful to refer to an isotropic radiator?
When comparing the gains of directional antennas
When testing a transmission line for standing wave ratio
When (in the northern hemisphere) directing the transmission in a southerly direction
When using a dummy load to tune a transmitter
Most AM broadcasts employ ___ polarization while most FM broadcasts employ ___ polarization of the radio wave.
vertical, vertical
vertical, horizontal
horizontal, vertical
horizontal, horizontal
How does the gain of a parabolic dish type antenna change when the operating frequency is doubled?
Gain does not change
Gain is multiplied by 0.707
Gain increases 6 dB
Gain increases 3 dB
What is the frequency range of an aircraft’s Very High Frequency (VHF) communications?
118.000 MHz to 136.975 MHz (worldwide up to 151.975 MHz)
108.000 MHz to 117.95 MHz
329.15 MHz to 335.00 MHz
2.0000 MHz to 29.999 MHz
What is a selective fading effect?
A fading effect caused by small changes in beam heading at the receiving station.
A fading effect caused by phase differences between radio wave components of the same transmission, as experienced at the receiving station.
A fading effect caused by large changes in the height of the ionosphere, as experienced at the receiving station
A fading effect caused by time differences between the receiving and transmitting stations.
If the velocity of propagation in a certain medium is 200×106 m/s, what is its refractive index?
1.3
1.5
1.27
0.67
What is the resultant field strength at the receiving antenna in space wave propagation under case 2?
0
ξd
2ξd
3ξd
The decimetric wave is using what method of propagation?
Ground wave
Space wave
Sky wave
Tropospheric wave
