High frequency (HF) radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters (ten to one hundred metres). Frequencies immediately below HF are denoted Medium-frequency (MF), and the next higher frequencies are known as Very high frequency (VHF). The Shortwave range (2.310 - 25.820 MHz) used by international broadcasters is part of the HF frequency spectrum. In aviation virtually the entire spectrum (2 - 29.999 MHz) is used for HF communications.

Propagation characteristics[link]

A modern Icom M700Pro two-way radio for marine HF radio communications.

The ionosphere often refracts HF radio waves quite well. This phenomenon is known as skywave propagation. Because of these characteristics this range is extensively used for medium and long range radio communication. However, suitability of this portion of the spectrum for such communication varies greatly with a complex combination of factors:

• Sunlight/darkness at site of transmission and reception
• Transmitter/receiver proximity to terminator
• Season
• Sunspot cycle
• Solar activity
• Polar aurora

These and other factors contribute, at each point in time for a given communication path, to a

• Maximum usable frequency (MUF)
• Lowest usable high frequency (LUF) and a
• Frequency of optimum transmission (FOT)

The maximum usable frequency regularly drops below 10 MHz in darkness during the winter months, while in summer during daylight it can easily surpass 30 MHz. It depends on the angle of incidence of the waves; it is lowest when the waves are directed straight upwards, and is higher with less acute angles. This means that at longer distances, where the waves graze the ionosphere at a very blunt angle, the MUF may be much higher. The lowest usable frequency depends on the absorption in the lower layer of the ionosphere (the D-layer). This absorption is stronger at low frequencies and is also stronger with increased solar activity (for example in daylight); total absorption often occurs at frequencies below 5 MHz during daytime. The result of these two factors is that the usable spectrum shifts towards the lower frequencies and into the Medium Frequency (MF) range during winter nights, while on a day in full summer the higher frequencies tend to be more usable, often into the lower VHF range.^{[citation needed]}

Exploitation of, and limits imposed by, these characteristics[link]

When all factors are at their optimum, worldwide communication is possible on HF. At many other times it is possible to make contact across and between continents or oceans. At worst, when a band is 'dead', no communication beyond the limited groundwave paths is possible no matter what powers, antennas or other technologies are brought to bear. When a transcontinental or worldwide path is open on a particular frequency, digital, SSB and Morse code communication is possible using surprisingly low transmission powers, often of the order of tens of watts, provided suitable antennas are in use at both ends and that there is little or no man-made or natural interference.^[1] On such an open band, interference originating over a wide area affects many potential users. These issues are significant to military, safety^[2] and amateur radio users of the HF bands.

Uses[link]

An amateur radio station incorporating two HF transceivers.

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.

However, the development of Automatic Link Establishment technology based on MIL-STD-188-141 for automated connectivity and frequency selection, along with the high costs of satellite usage, have led to a renaissance in HF usage in government networks. The development of higher speed modems such as those conforming to MIL-STD-188-110C which support data rates up to 120 kilobit/s has also increased the usability of HF for data communications and video transmission. Other standards development such as STANAG 5066 provides for error free data communications through the use of ARQ protocols.

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.

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 has 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. Other electronic devices including plasma televisions can also have a detrimental effect on the HF spectrum.

In Aviation, HF communication systems are required for all trans-oceanic flights. These systems incorporate frequencies down to 2 MHz to include a 2182 kHz station known as "Compulsory Channel Watch".^{[citation needed]}

Some radio frequency identification (RFID) tags utilize HF. These tags are commonly known as HFID's or HighFID's (High Frequency Identification).

See also[link]

• High Frequency Active Auroral Research Program
• High Frequency Internet Protocol
• Low frequency
• Radio propagation
• Space weather

References[link]

1. ^ Paul Harden (2005). "Solar Activity & HF Propagation". QRP Amateur Radio Club International. http://www.qrparci.org/content/view/58/118/. Retrieved 2009-02-22. 
2. ^ "Amateur Radio Emergency Communication". American Radio Relay League, Inc.. 2008. http://www.arrl.org/pio/emergen1.html. Retrieved 2009-02-22. ^{[dead link]}

Further reading[link]

• Maslin, N.M. "HF Communications - A Systems Approach". ISBN 0-273-02675-5, Taylor & Francis Ltd, 1987
• Johnson, E.E., et al., "Advanced High-Frequency Radio Communications". ISBN 0-89006-815-1, Artech House, 1997
• V. Narayanamurti, et al., "Selective Transmission of High-Frequency Phonons by a Superlattice: The "Dielectric" Phonon Filter". Phys. Rev. Lett. 43, 2012–2016 (Issue 27 – 31 December 1979).
• Boulos-Paul Bejjani, et al., "Transient Acute Depression Induced by High-Frequency Deep-Brain Stimulation". New England Journal of Medicine, Volume 340:1476-1480 May 13, 1999 Number 19. Massachusetts Medical Society.
• H. C. Liu, "Analytical model of high-frequency resonant tunneling: The first-order ac current response". Phys. Rev. B 43, 12538–12548 (Issue 15 – 15 May 1991).
• Sipila, M., et al., "High-frequency periodic time-domain waveform measurement system". IEEE Transactions on Microwave Theory and Techniques, Volume 36, Issue 10, pg. 1397-1405, Oct 1988. ISSN 0018-9480 INSPEC 3291255 DOI 10.1109/22.6087
• Morched, A., et al., "A high frequency transformer model for the EMTP". IEEE Transactions on Power Delivery, Volume 8, Issue 3, pg. 1615-1626, Jul 1993. ISSN 0885-8977 INSPEC 4581865 DOI 10.1109/61.252688

External links[link]

• Tomislav Stimac, "Definition of frequency bands (VLF, ELF... etc.)". IK1QFK Home Page (vlf.it).
• Douglas C. Smith, High Frequency Measurements Web Page; Index and Technical Tidbits. D. C. Smith Consultants, Los Gatos, CA.
• High Frequency Propagation Models, its.bldrdoc.gov.
• High Frequency Wave Propagation, cscamm.umd.edu.
• "Grounding for Low- and High-Frequency Circuits" (PDF)
• "High frequency noise" (PDF)
• "Advantages of HF Radio" Codan
• Solar conditions for HF-radio

For other uses of the title The Grid, see Grid (disambiguation).

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (October 2010)

The Grid are an English electronic dance group, consisting of Richard Norris and David Ball (formerly of Soft Cell),^[1] with guest contributions from other musicians. They are best known for the hits "Swamp Thing", "Crystal Clear", "Rollercoaster", "Floatation", and "Cybernetic" (with Robert Fripp and Phil Manzanera).

Band members[link]

• Richard Norris (born 23 June 1965, London) - keyboards
• David Ball (born 3 May 1959, Blackpool, Lancashire) - keyboards
• Sacha Rebecca Souter (musician) (born 26 November 1963, Cockerton, County Durham) - Vocals

Biography[link]

The Grid formed in 1988 and had their first success with debut single, "Floatation", released on East West Records in 1990. They went on to release a string of ten UK hit singles and four albums,^[1] and toured the UK, Europe, Asia and Australia. The group's 1994 album Evolver reached #14 in the UK Albums Chart.^[1] The lead single from this album, "Swamp Thing", featuring elaborate banjo lines played by Roger Dinsdale. "Swamp Thing" proved to be a commercial success in the UK, Europe and Australia, reaching #3 in the UK^[1] and Australia and selling a total of one million copies.^{[citation needed]}

In 1996, Norris and Ball agreed to a hiatus period in order pursue individual music interests. Norris formed the Droyds, which went on to remix tracks by musicians including Armand Van Helden and Siobhan Fahey, and wrote the official biography of Paul Oakenfold (published in 2007): Ball reformed Soft Cell with Marc Almond, and also wrote music scores for films.^{[citation needed]} Norris has since formed the psychedelic duo, Beyond The Wizard's Sleeve, with DJ Erol Alkan, and has released a number of solo records and remixes under the name The Time and Space Machine.

The duo reunited in 2005, initially playing two gigs under the name GDM with female singer Misty Woods, before writing and recording new material as the Grid. A single, "Put Your Hands Together", was released in 2007 and an album, Doppelgänger, followed in 2008. Both were released on the Some Bizzare label. The album featured vocals by the British musician, Chris Braide.

Discography[link]

Albums[link]

Singles[link]

References[link]

External links[link]

• Grid Central - An Unofficial Page for The Grid
• Death of Roger Dinsdale.
• The Grid on allmusic.com
• The Grid MySpace page