Radio Wave Propagation Flashcards

What is 'aurora propagation' and on which frequency bands is it most commonly observed?

Answer: Propagation via ionization in auroral curtains, most commonly observed on VHF (50 MHz and 144 MHz)

Aurora propagation uses the dense ionization in auroral curtains to scatter radio waves, providing unusual VHF contacts (especially on 6m and 2m) during geomagnetic storms, though signals have a characteristic buzzing distortion.

What is 'transequatorial propagation' (TEP) in VHF radio?

Answer: Long-distance propagation across the magnetic equator enabled by F-layer irregularities on either side of it

TEP is a form of ionospheric propagation at VHF (50–144 MHz) that occurs when signals from stations north and south of the geomagnetic equator are scattered by spread-F irregularities in the F layer on both sides of the equator.

What effect does high atmospheric humidity have on microwave signal propagation?

Answer: Water vapor absorbs microwave energy, increasing path attenuation especially at frequencies above about 10 GHz

Water vapor absorbs microwave energy, with absorption peaks near 22 GHz and 60 GHz, significantly increasing path loss in humid conditions and during rain at frequencies above roughly 10 GHz.

What is the 'critical frequency' of the ionosphere?

Answer: The highest frequency that is reflected straight back (vertically) by a given ionospheric layer

The critical frequency (fc) is the highest frequency that is reflected straight back by a given ionospheric layer when a signal is transmitted vertically; frequencies above fc pass through that layer at vertical incidence.

Which antenna characteristic is most important for minimizing sky-wave interference on a ship's MF/HF station when communicating via ground wave?

Answer: High vertical gain to maximize the signal toward the horizon

For ground-wave communication, maximum radiation at low elevation angles (toward the horizon) is desired, and high-angle sky-wave radiation may be minimized to reduce interference from sky-wave returns at other distances.

What is 'radio horizon' and how does it differ from the optical horizon?

Answer: The radio horizon is typically about 15% farther than the optical horizon because of atmospheric refraction of radio waves

Atmospheric refraction bends radio waves slightly downward along the Earth's curvature, extending the radio horizon approximately 15% beyond the optical horizon; engineers use an effective Earth radius of 4/3 the actual radius for path calculations.

What is 'meteor scatter' propagation used for in radio communications?

Answer: Short-duration VHF propagation using ionized meteor trails, typically for 50 MHz and 144 MHz contacts over 500–2000 km

Meteor scatter uses the brief ionized trails left by meteors entering the atmosphere to reflect VHF signals, enabling contacts of 500–2,000 km on 50 MHz and 144 MHz, typically lasting only seconds and often during known meteor showers.