Ham Radio General Class Test Radio Wave Propagation 4 — Questions and Answers
Question 1: What is 'tropospheric scatter' (tropo scatter) propagation?
- Refraction of signals through the ionosphere at low elevation angles
- Scattering of VHF/UHF signals by turbulence and irregularities in the troposphere, enabling paths of 200-800+ km (Correct answer)
- Signals scattered off mountain ranges in the troposphere
- Ducting of signals along the surface of the Earth
Correct answer: Scattering of VHF/UHF signals by turbulence and irregularities in the troposphere, enabling paths of 200-800+ km
Troposcatter uses the forward scatter of signals from irregularities in the troposphere to achieve beyond-line-of-sight paths at VHF/UHF, typically 200-800+ km.
Question 2: What is 'sporadic-E' (Es) propagation and what frequencies does it most affect?
- Smooth, predictable E-layer propagation affecting 160 meters in winter
- Unpredictable clouds of ionization in the E layer that support propagation on 6 meters, 10 meters, and even 2 meters (Correct answer)
- Enhanced F2 propagation on 20 and 40 meters during summer
- D-layer scatter affecting frequencies below 3 MHz
Correct answer: Unpredictable clouds of ionization in the E layer that support propagation on 6 meters, 10 meters, and even 2 meters
Sporadic-E consists of intense, localized patches of ionization at E-layer heights that can support propagation on frequencies from HF into VHF, often unexpectedly.
Question 3: How does antenna take-off angle affect skip distance on HF?
- Higher take-off angles produce shorter skip distances; lower angles produce longer skip distances (Correct answer)
- Take-off angle has no effect on skip distance; only frequency matters
- Lower take-off angles always produce shorter, more reliable paths
- Higher take-off angles always produce the longest possible skip
Correct answer: Higher take-off angles produce shorter skip distances; lower angles produce longer skip distances
A high take-off angle returns a sky-wave closer to the transmitter (short skip), while a low take-off angle at the horizon returns a wave much farther away (long skip/DX).
Question 4: What is 'ionospheric tilt' and how can it affect communications?
- A permanent slope in the F layer toward the poles that absorbs equatorial signals
- An uneven or tilted ionospheric layer that can cause signals to be reflected in unexpected directions (Correct answer)
- The daily migration of the F layer from east to west
- The angle of the E layer relative to the Earth's surface at the equator
Correct answer: An uneven or tilted ionospheric layer that can cause signals to be reflected in unexpected directions
Ionospheric tilt, often caused by solar terminator gradients or geomagnetic activity, can deflect signals off their expected path, enabling unusual contacts or causing propagation anomalies.
Question 5: What is the Lowest Usable Frequency (LUF) determined by?
- The frequency at which the antenna becomes too large to be practical
- The frequency below which D-layer absorption makes a path unusable despite adequate MUF (Correct answer)
- The minimum frequency regulated by the FCC for amateur use
- The frequency below which ionospheric refraction does not occur
Correct answer: The frequency below which D-layer absorption makes a path unusable despite adequate MUF
The LUF is the lowest frequency on which D-layer absorption is low enough to allow adequate signal strength over a given path — it rises during solar events.
Question 6: What propagation mode allows contacts on 2-meter FM when a temperature inversion is present?
- Sporadic-E
- Meteor scatter
- Tropospheric ducting (Correct answer)
- F2 skip
Correct answer: Tropospheric ducting
Temperature inversions in the lower atmosphere create a refractive duct that can guide 2-meter signals well beyond normal line-of-sight range through tropospheric ducting.
Question 7: Which of the following best describes 'meteor scatter' propagation?
- Signals refracted by large meteorite impact craters
- Brief ionized trails left by meteors entering the atmosphere used to reflect VHF signals over 800-2,000 km paths (Correct answer)
- HF propagation assisted by increased ionization from meteor showers
- A mode used only on frequencies below 1 MHz
Correct answer: Brief ionized trails left by meteors entering the atmosphere used to reflect VHF signals over 800-2,000 km paths
Meteors burn up in the atmosphere leaving brief ionized trails that reflect VHF signals (typically 50-144 MHz) over paths of 800-2,000 km in short bursts.
Ham Radio General Class Test Radio Wave Propagation 4
What is 'tropospheric scatter' (tropo scatter) propagation?