SUBELEMENT T3 – RADIO WAVE PROPAGATION Flashcards by Jon Sessions

Why do VHF signal strengths sometimes vary greatly when the antenna is moved only a few feet? T3A01
A. The signal path encounters different concentrations of water vapor
B. VHF ionospheric propagation is very sensitive to path length
C. Multipath propagation cancels or reinforces signals
D. All these choices are correct

C. Multipath propagation cancels or reinforces signals

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What is the effect of vegetation on UHF and microwave signals? T3A02
A. Knife-edge diffraction
B. Absorption
C. Amplification
D. Polarization rotation

B. Absorption

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What antenna polarization is normally used for long-distance CW and SSB contacts on the VHF and UHF bands? T3A03
A. Right-hand circular
B. Left-hand circular
C. Horizontal
D. Vertical

C. Horizontal

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What happens when antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization? T3A04
A. The modulation sidebands might become inverted
B. Received signal strength is reduced
C. Signals have an echo effect
D. Nothing significant will happen

B. Received signal strength is reduced

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When using a directional antenna, how might your station be able to communicate with a distant repeater if buildings or obstructions are blocking the direct line of sight path? T3A05
A. Change from vertical to horizontal polarization
B. Try to find a path that reflects signals to the repeater
C. Try the long path
D. Increase the antenna SWR

B. Try to find a path that reflects signals to the repeater

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What is the meaning of the term “picket fencing”? T3A06
A. Alternating transmissions during a net operation
B. Rapid flutter on mobile signals due to multipath propagation
C. A type of ground system used with vertical antennas
D. Local vs long-distance communications

B. Rapid flutter on mobile signals due to multipath propagation

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What weather condition might decrease range at microwave frequencies? T3A07
A. High winds
B. Low barometric pressure
C. Precipitation
D. Colder temperatures

C. Precipitation

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What is a likely cause of irregular fading of signals propagated by the ionosphere? T3A08
A. Frequency shift due to Faraday rotation
B. Interference from thunderstorms
C. Intermodulation distortion
D. Random combining of signals arriving via different paths

D. Random combining of signals arriving via different paths

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Which of the following results from the fact that signals propagated by the ionosphere are elliptically polarized? T3A09
A. Digital modes are unusable
B. Either vertically or horizontally polarized antennas may be used for transmission or reception
C. FM voice is unusable
D. Both the transmitting and receiving antennas must be of the same polarization

B. Either vertically or horizontally polarized antennas may be used for transmission or reception

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What effect does multi-path propagation have on data transmissions? T3A10
A. Transmission rates must be increased by a factor equal to the number of separate paths observed
B. Transmission rates must be decreased by a factor equal to the number of separate paths observed
C. No significant changes will occur if the signals are transmitted using FM
D. Error rates are likely to increase

D. Error rates are likely to increase

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Which region of the atmosphere can refract or bend HF and VHF radio waves? T3A11
A. The stratosphere
B. The troposphere
C. The ionosphere
D. The mesosphere

C. The ionosphere

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What is the effect of fog and rain on signals in the 10 meter and 6 meter bands? T3A12
A. Absorption
B. There is little effect
C. Deflection
D. Range increase

B. There is little effect

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What is the relationship between the electric and magnetic fields of an electromagnetic wave? T3B01
A. They travel at different speeds
B. They are in parallel
C. They revolve in opposite directions
D. They are at right angles

D. They are at right angles

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What property of a radio wave defines its polarization? T3B02
A. The orientation of the electric field
B. The orientation of the magnetic field
C. The ratio of the energy in the magnetic field to the energy in the electric field
D. The ratio of the velocity to the wavelength

A. The orientation of the electric field

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What are the two components of a radio wave? T3B03
A. Impedance and reactance
B. Voltage and current
C. Electric and magnetic fields
D. Ionizing and non-ionizing radiation

C. Electric and magnetic fields

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What is the velocity of a radio wave traveling through free space? T3B04
A. Speed of light
B. Speed of sound
C. Speed inversely proportional to its wavelength
D. Speed that increases as the frequency increases

A. Speed of light

What is the relationship between wavelength and frequency? T3B05
A. Wavelength gets longer as frequency increases
B. Wavelength gets shorter as frequency increases
C. Wavelength and frequency are unrelated
D. Wavelength and frequency increase as path length increases

B. Wavelength gets shorter as frequency increases

What is the formula for converting frequency to approximate wavelength in meters? T3B06
A. Wavelength in meters equals frequency in hertz multiplied by 300
B. Wavelength in meters equals frequency in hertz divided by 300
C. Wavelength in meters equals frequency in megahertz divided by 300
D. Wavelength in meters equals 300 divided by frequency in megahertz

D. Wavelength in meters equals 300 divided by frequency in megahertz

In addition to frequency, which of the following is used to identify amateur radio bands? T3B07
A. The approximate wavelength in meters
B. Traditional letter/number designators
C. Channel numbers
D. All these choices are correct

A. The approximate wavelength in meters

What frequency range is referred to as VHF? T3B08
A. 30 kHz to 300 kHz
B. 30 MHz to 300 MHz
C. 300 kHz to 3000 kHz
D. 300 MHz to 3000 MHz

B. 30 MHz to 300 MHz

What frequency range is referred to as UHF? T3B09
A. 30 to 300 kHz
B. 30 to 300 MHz
C. 300 to 3000 kHz
D. 300 to 3000 MHz

D. 300 to 3000 MHz

What frequency range is referred to as HF? T3B10
A. 300 to 3000 MHz
B. 30 to 300 MHz
C. 3 to 30 MHz
D. 300 to 3000 kHz

C. 3 to 30 MHz

What is the approximate velocity of a radio wave in free space? T3B11
A. 150,000 meters per second
B. 300,000,000 meters per second
C. 300,000,000 miles per hour
D. 150,000 miles per hour

B. 300,000,000 meters per second

Why are simplex UHF signals rarely heard beyond their radio horizon? T3C01
A. They are too weak to go very far
B. FCC regulations prohibit them from going more than 50 miles
C. UHF signals are usually not propagated by the ionosphere
D. UHF signals are absorbed by the ionospheric D region

C. UHF signals are usually not propagated by the ionosphere

**What is a characteristic of HF communication compared with communications on VHF and higher frequencies?** T3C02 A. HF antennas are generally smaller B. HF accommodates wider bandwidth signals C. Long-distance ionospheric propagation is far more common on HF D. There is less atmospheric interference (static) on HF

C. Long-distance ionospheric propagation is far more common on HF

**What is a characteristic of VHF signals received via auroral backscatter?** T3C03 A. They are often received from 10,000 miles or more B. They are distorted and signal strength varies considerably C. They occur only during winter nighttime hours D. They are generally strongest when your antenna is aimed west

B. They are distorted and signal strength varies considerably

**Which of the following types of propagation is most commonly associated with occasional strong signals on the 10, 6, and 2 meter bands from beyond the radio horizon? T3C04 A. Backscatter B. Sporadic E C. D region absorption D. Gray-line propagation

B. Sporadic E

**Which of the following effects may allow radio signals to travel beyond obstructions between the transmitting and receiving stations?** T3C05 A. Knife-edge diffraction B. Faraday rotation C. Quantum tunneling D. Doppler shift

A. Knife-edge diffraction

**What type of propagation is responsible for allowing over-the-horizon VHF and UHF communications to ranges of approximately 300 miles on a regular basis?** T3C06 A. Tropospheric ducting B. D region refraction C. F2 region refraction D. Faraday rotation

A. Tropospheric ducting

**What band is best suited for communicating via meteor scatter?** T3C07 A. 33 centimeters B. 6 meters C. 2 meters D. 70 centimeters

B. 6 meters

**What causes tropospheric ducting?** T3C08 A. Discharges of lightning during electrical storms B. Sunspots and solar flares C. Updrafts from hurricanes and tornadoes D. Temperature inversions in the atmosphere

D. Temperature inversions in the atmosphere

**What is generally the best time for long-distance 10 meter band propagation via the F region?** T3C09 A. From dawn to shortly after sunset during periods of high sunspot activity B. From shortly after sunset to dawn during periods of high sunspot activity C. From dawn to shortly after sunset during periods of low sunspot activity D. From shortly after sunset to dawn during periods of low sunspot activity

A. From dawn to shortly after sunset during periods of high sunspot activity

**Which of the following bands may provide long-distance communications via the ionosphere’s F region during the peak of the sunspot cycle?** T3C10 A. 6 and 10 meters B. 23 centimeters C. 70 centimeters and 1.25 meters D. All these choices are correct

A. 6 and 10 meters

**Why is the radio horizon for VHF and UHF signals more distant than the visual horizon?** T3C11 A. Radio signals move somewhat faster than the speed of light B. Radio waves are not blocked by dust particles C. The atmosphere refracts radio waves slightly D. Radio waves are blocked by dust particles

C. The atmosphere refracts radio waves slightly