Chapter 4: Propagation, Antennas And Feed Lines Flashcards
What should you do if another operator reports that your station’s 2 meter signals were strong just a moment ago, but now they are weak or distorted?
Moving or re-orienting your antenna
Why might the range of VHF and UHF signals be greater in the winter?
Lush vegetation can absorb VHF and UHF radio waves
What term is commonly used to describe the rapid fluttering sound sometimes heard from mobile stations that are moving while transmitting?
Mobile flutter or picket-fencing
Which of the following is a likely cause of irregular fading of signals received by ionospheric reflection?
Multi-path propagation
What may occur if data signals arrive via multiple paths?
Distortion may cause data signals to be received with a higher error rate, even with a strong signal
How might fog and light rain affect radio change on 10 meters and 6 meters?
Precipitation such as fog and rain can absorb microwave and UHF radio waves although it has little effect at HF and lower VHF
What weather conditions would decrease range at microwave frequencies?
Precipitation such as fog or rain
Which of the following effects might cause radio signals to be heard despite obstructions between the transmitting and receiving stations?
Diffraction, also called “knife-edge diffraction” due to the waves ability to travel past sharp edges of large objects
What mode is responsible for allowing over-the-horizon VHF and UHF communications to ranges of approximately 300 miles on a regular basis?
Tropospheric propagation, or “tropo”, is used by amateurs to make VHF and UHF contacts over long distances
What causes tropospheric ducting?
Variations such as weather fronts and temperature inversions create layers of air next to each other that have different characteristics. Layers form structures called “ducts” that can guide microwave signals for long distances.
Why do VHF and UHF radio signals usually travel somewhat farther than the visual line of sight distance between two stations?
By bending the signals slightly back towards the ground, refraction counteracts the curvature of the Earth and allows signals to be received at distances somewhat beyond the visual horizon.
Which part of the atmosphere enables the propagation of radio signals around the world?
The Ionosphere
Why are direct (not via a repeater) UHF signals rarely heard from stations outside your local coverage area?
UHF signals usually pass through the ionosphere with only a little bending and are lost to space
Which of the following is an advantage of HF vs VHF and higher frequencies?
At VHF and higher frequencies, the waves usually pass through the ionosphere with only a little bending and are lost to space.
What is a characteristic of VHF signals received via auroral reflection?
Because the auroral is constantly changing, the reflected signals change strength quickly and are often distorted.
Which of the following propagation types is most commonly associated with occasional strong over-the-horizon signals on 10, 6, and 2 meter bands?
Sporadic E, or E-skip, propagation. Most common during early summer and mid-winter months on 10, 6, and 2 meter bands
What band is best suited for communicating via meteor scatter?
6 meter, with contacts being made up to distances of 1200 to 1500 miles
What is generally the best time for long-distance 10 meter band propagation via the F layer?
From dawn until shortly after sunset
Which of the following bands may provide long distance communications during the peak of the sunspot cycle?
Upper HF bands (10m, occasionally 6m)
What can happen if the antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization?
What polarization’s aren’t aligned the receding signal can be dramatically reduced. Less current is also created by the antenna.
What type of wave carries radio signals between transmitting and receiving stations?
An electromagnetic wave
Which of the following results from the fact that skip signals refracted from the ionosphere are elliptically polarized?
A receiving antenna of any polarization will respond to the incoming wave at least partially. This means that both vertical and horizontal antennas are effective for receiving and transmitting on the HF bands where skip propagation is common.
What property of a radio wave is used to describe its polarization?
A radio wave’s electric field
What are the two components of a radio wave?
An electric field and a magnetic field.
A radio wave is made up of what type of energy?
Electromagnetic energy
What is the gain of an antenna?
The ability of an antenna to concentrate radiated signals in a specific direction.
