High frequency (HF) radio frequencies are between 3 and 30 MHz. This range is often called shortwave. Radio Wave is also the name of a commercial radio station in Blackpool, North West England. ... A megahertz (MHz) is one million (106) hertz, a measure of frequency. ... A Grundig Shortwave receiver Shortwave radio operates between the frequencies of 3,000 kHz and 30 MHz (30,000 kHz) and came to be referred to as such in the early days of radio because the wavelengths associated with this frequency range were shorter than those commonly in use at...

Since the ionosphere often reflects HF radio waves quite well, this range is extensively used for medium and long range terrestrial radio communication. However, suitability of this portion of the spectrum for such communication varies greatly with a complex combination of factors: The ionosphere is the part of the atmosphere that is ionized by solar radiation. ... The word reflection (also spelt reflexion in British English) can refer to several different concepts: In mathematics, reflection is the transformation of a space. ...

• Sunlight/darkness at site of transmission and reception
• Transmitter/receiver proximity to terminator
• Season
• Sunspot cycle
• Solar activity
• Polar aurora
• Maximum usable frequency
• Lowest usable frequency
• Frequency of operation within the HF range

The high frequency band is very popular with amateur radio operators, who can take advantage of direct, long-distance (often inter-continental) communications and the "thrill factor" resulting from making contacts in variable conditions. International shortwave broadcasting utilizes this set of frequencies, as well as a seemingly declining number of "utility" users (marine, aviation, military, and diplomatic interests), who have, in recent years, been swayed over to less volatile means of communication (for example, via satellites), but may maintain HF stations after switch-over for back-up purposes. CB radios operate in the higher portion of the range (around 27 MHz), as do some studio-to-transmitter (STL) radio links. Some modes of communication, such as continuous wave morse code transmissions (especially by amateur radio operators) and single sideband voice transmissions are more common in the HF range than on other frequencies, because of their bandwidth-conserving nature, but broadband modes, such as TV transmissions, are generally prohibited by HF's relatively small chunk of electromagnetic spectrum space. A composite image showing the terminator crossing Europe and Africa The terminator is the line between the illuminated, day side and dark, night side of a planetary body (also known as the grey line). It is defined as the locus of points on a moon or planet where the line... A season is one of the major divisions of the year, generally based on yearly periodic changes in weather. ... 400 year sunspot history A sunspot is a region on the Suns surface (photosphere) that is marked by a lower temperature than its surroundings, and intense magnetic activity. ... A sunspot is a region on the Suns surface (photosphere) that is marked by a lower temperature than its surroundings, and intense magnetic activity. ... Aurora borealis Polar aurorae are optical phenomena characterized by colorful displays of light in the night sky. ... Maximum usable frequency (MUF) describes, in radio transmission, using reflection from the regular ionized layers of the ionosphere, the upper frequency limit that can be used for transmission between two points at a specified time. ... Mrs. ... A Grundig Shortwave receiver Shortwave radio operates between the frequencies of 3,000 kHz and 30 MHz (30,000 kHz) and came to be referred to as such in the early days of radio because the wavelengths associated with this frequency range were shorter than those commonly in use at... A satellite is an object that orbits another object (known as its primary). ... CB may be: Cambridge: CB is the British post code for the region in eastern England which is served by the Cambridge postal sorting office. ... A continuous wave (CW) is an electromagnetic wave of constant amplitude and frequency. ... Morse code is a system of representing letters, numbers and punctuation marks by means of a code signal sent intermittently. ... Mrs. ... SSB might be an acronym or abbreviation for: Single-sideband modulation strategic system builder Single-strand binding protein. ... The electromagnetic spectrum is the range of all possible electromagnetic radiation. ...

Noise, especially man-made interference from electronic devices, tends to have a great effect on the HF bands. In recent years, concerns have risen among certain users of the HF spectrum over "broadband over power lines" (BPL) Internet access, which is believed to have an almost destructive effect on HF communications. This is due to the frequencies on which BPL operates (typically corresponding with the HF band) and the tendency for the BPL "signal" to leak from power lines. Some BPL providers have installed "notch filters" to block out certain portions of the spectrum (namely the amateur radio bands), but a great amount of controversy over the deployment of this access method remains. Power line communication (PLC), also called Broadband over Power Lines (BPL), is wireline method of communication using the existing electric power transmission and electricity distribution lines. ...

See also

• VHF, AM radio, Radio propagation