Terms related to HF radio propagation

Knowing the terminology used in HF radio propagation can help you understand long-distance communication via skywaves.

Find below a glossary of basic terms and an extended index of terms related to HF radio propagation:

A glossary of basic terms

Frequency (f): The number of cycles of a radio wave that occur in one second, measured in Hertz (Hz).
Wavelength (λ): The distance between two consecutive points in a wave, usually measured in meters (m). In radio, wavelength and frequency are inversely related: longer wavelengths correspond to lower frequencies, and vice versa.
Ionosphere: A region of the Earth's upper atmosphere (approximately 30 to 250 miles above the surface) where ionization occurs due to solar radiation. The ionosphere plays a crucial role in HF radio propagation by reflecting and refracting radio waves.
Skywave Propagation: The phenomenon in which HF radio waves are refracted back to Earth's surface by the ionosphere. This allows for long-distance communication beyond the line of sight.
Groundwave Propagation: Radio waves that travel along the Earth's surface, providing communication over relatively short distances, typically up to a few hundred miles.
Skip Distance: The minimum distance from the transmitter at which a radio wave can be received after undergoing skywave propagation. This distance depends on the frequency and angle of incidence.v
Skip Zone / Dead Zone : The region between the groundwave coverage area and the first hop of the skywave propagation, where reception is poor or nonexistent.
MUF (Maximum Usable Frequency): The highest frequency at which skywave propagation is reliably achievable between two points on Earth during a specific time and under specific ionospheric conditions.
LUF (Lowest Usable Frequency): The lowest frequency at which skywave propagation is reliably achievable under specific ionospheric conditions.
Fading: The variation in signal strength and quality experienced during radio transmission due to changes in ionospheric conditions, interference, or other factors.v
D-layer: The lowest layer of the ionosphere, located at an altitude of approximately 30 to 60 miles. The D-layer absorbs HF radio waves during daylight hours, affecting propagation.
E-layer: Located above the D-layer, the E-layer is responsible for sporadic E-skip propagation, which can enable HF communication at higher frequencies.
F-layer: The F-layer of the ionosphere consists of two sub-layers, F1 and F2, and is the primary layer for HF propagation. The F2 layer is particularly important for long-distance communication.
Critical Frequency (fc): The highest frequency that can be transmitted vertically and still return to Earth via skywave propagation.
Optimum Working Frequency (OWF): The frequency that provides the best propagation conditions for a given HF communication path.
Solar Flux Index (SFI): A measure of the sun's radio emissions at a specific wavelength (usually 10.7 cm). It is used as an indicator of solar activity, which affects ionospheric conditions and HF propagation.
A-index: A daily measure of geomagnetic activity on a scale from 0 to 400, with lower values indicating quieter geomagnetic conditions. Geomagnetic activity can disrupt HF propagation.

Extended index of terms

The following is an alphabetical list of terms related to HF radio propagation:

If no flags are displayed, it means that the flagcounter website is down!