T3_Radio_Wave_Propagation

Why do VHF signal strengths sometimes vary greatly when the antenna is moved only a few feet?

• The signal path encounters different concentrations of water vapor
• VHF ionospheric propagation is very sensitive to path length
• . Multipath propagation cancels or reinforces signals
• All these choices are correct

What is the effect of vegetation on UHF and microwave signals?

• Knife-edge diffraction
• Absorption
• Amplification
• Polarization rotation

What antenna polarization is normally used for long-distance CW and SSB contacts on the VHF and UHF bands?

• Right-hand circular
• Left-hand circular
• Horizontal
• Vertical

What happens when antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization?

• The modulation sidebands might become inverted
• Received signal strength is reduced
• Signals have an echo effect
• Nothing significant will happen

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?

• Change from vertical to horizontal polarization
• Try to find a path that reflects signals to the repeater
• Try the long path
• Increase the antenna SWR

What is the meaning of the term “picket fencing”?

• Alternating transmissions during a net operation
• Rapid flutter on mobile signals due to multipath propagation
• A type of ground system used with vertical antennas
• Local vs long-distance communications

What weather condition might decrease range at microwave frequencies?

• High winds
• Low barometric pressure
• Precipitation
• Colder temperatures

What is a likely cause of irregular fading of signals propagated by the ionosphere?

• Frequency shift due to Faraday rotation
• Interference from thunderstorms
• Intermodulation distortion
• Random combining of signals arriving via different paths

Which of the following results from the fact that signals propagated by the ionosphere are elliptically polarized?

• Digital modes are unusable
• Either vertically or horizontally polarized antennas may be used for transmission or reception
• FM voice is unusable
• Both the transmitting and receiving antennas must be of the same polarization

What effect does multi-path propagation have on data transmissions?

• Transmission rates must be increased by a factor equal to the number of separate paths observed
• Transmission rates must be decreased by a factor equal to the number of separate paths observed
• No significant changes will occur if the signals are transmitted using FM
• Error rates are likely to increase