Radio Wave Propagation Flashcards
7 cards from real GROL practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Radio Wave Propagation flashcards as text
What is a 'solar flare' and how does it affect HF radio propagation?
Answer: A burst of radiation from the Sun that intensifies D-layer absorption, causing sudden HF blackouts
Solar flares release intense X-ray bursts that dramatically increase D-layer ionization on the sunlit side of Earth, causing sudden ionospheric disturbances (SIDs) that absorb and black out HF signals.
What is a geomagnetic storm's primary effect on HF propagation?
Answer: It disrupts the F2 layer and degrades or eliminates HF propagation, especially at high latitudes
Geomagnetic storms, caused by solar wind interacting with Earth's magnetic field, disturb and deplete the F2 layer, reducing the MUF and causing widespread HF propagation degradation, worst at high latitudes.
What is 'ionospheric scatter' propagation?
Answer: Scattering of radio waves by irregularities in the ionosphere, used for beyond-line-of-sight links at VHF
Ionospheric scatter relies on weak scattering by irregularities in the lower ionosphere (D/E layers) to achieve beyond-line-of-sight VHF links over 1,000–2,000 km, though signals are weak and require high-power equipment.
What is tropospheric scatter (troposcatter) propagation?
Answer: Beyond-line-of-sight propagation at UHF/SHF caused by scattering in the troposphere
Troposcatter uses scattering by turbulent eddies and refractive index variations in the troposphere to achieve reliable UHF/SHF links over 300–800 km beyond line of sight, widely used in military and point-to-point systems.
What is 'selective fading' in HF communications?
Answer: Fading in which different frequencies within a signal's bandwidth fade independently, distorting the signal
Selective fading occurs when multipath signals cause different frequency components of a wideband signal to fade at different rates, distorting the signal shape; this is especially problematic for wideband data signals on HF.
What is the 'gray line' in HF propagation?
Answer: The twilight zone at the terminator between day and night, where HF propagation is often enhanced
The gray line (terminator) is the boundary between daylit and dark regions of Earth; along this zone the D layer is absent while the F layer remains ionized, creating a brief window of enhanced long-distance HF propagation.
How does the ionosphere behave differently at night compared to daytime on HF bands?
Answer: The D and E layers weaken or disappear at night, reducing absorption and allowing lower HF frequencies to propagate farther via the F layer
At night the D and E layers recombine and disappear, eliminating their absorption, while the F1 and F2 layers merge into a single F layer; this dramatically improves propagation on lower HF bands (160m, 80m) after dark.