High frequency

High frequency

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High frequency radio frequencies
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...

 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)
Medium frequency
Medium frequency refers to radio frequencies in the range of 300 kHz to 3 MHz. Part of this band is the medium wave AM broadcast band. The MF band is also known as the hectometer band or hectometer wave as the wavelengths range from ten down to one hectometers...

, and the next higher frequencies are known as Very high frequency (VHF). The Shortwave
Shortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...

 range (2.310 - 25.820 MHz) used by international broadcasters is part of the HF frequency spectrum.

Propagation characteristics


Since the ionosphere
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...

 often refracts
Refraction
Refraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...

 HF radio waves quite well (a phenomenon known as skywave propagation
Skywave
Skywave is the propagation of electromagnetic waves bent back to the Earth's surface by the ionosphere. As a result of skywave propagation, a broadcast signal from a distant AM broadcasting station at night, or from a shortwave radio station can sometimes be heard as clearly as local...

), 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
    Terminator (solar)
    A terminator, twilight zone or "grey line" is a moving line that separates the illuminated day side and the dark night side of a planetary body...

  • Season
    Season
    A season is a division of the year, marked by changes in weather, ecology, and hours of daylight.Seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earth's axis relative to the plane of revolution...

  • Sunspot cycle
  • Solar activity
    Sunspot
    Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature....

  • Polar aurora


These and other factors contribute, at each point in time for a given communication path, to a
  • Maximum usable frequency
    Maximum usable frequency
    Maximum usable frequency 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, independent of transmitter power...

     (MUF)
  • Lowest usable high frequency
    Lowest usable high frequency
    The lowest usable high frequency , in radio transmission, is that frequency in the HF band at which the received field intensity is sufficient to provide the required signal-to-noise ratio for a specified time period, e.g., 0100 to 0200 UTC, on 90% of the undisturbed days of the month...

     (LUF) and a
  • Frequency of optimum transmission
    Frequency of optimum transmission
    Frequency of optimum transmission, in the transmission of radio waves via ionospheric reflection, is the highest effective frequency that is predicted to be usable for a specified path and time for 90% of the days of the month. It is often abbreviated as FOT. The FOT is normally just below the...

     (FOT)

Exploitation of, and limits imposed by, these characteristics


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 CW
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...

 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. On such an open band, interference originating over a wide area affects many potential users. These issues are significant to military, safety and amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...

 users of the HF bands.

Uses



The high frequency band is very popular with amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...

 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
Shortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...

 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 satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

s), but may maintain HF stations after switch-over for back-up purposes. However, the development of Automatic Link Establishment
Automatic link establishment
Automatic Link Establishment, commonly known as ALE, is the worldwide de facto standard for digitally initiating and sustaining HF radio communications. ALE is a feature in an HF communications radio transceiver system, that enables the radio station to make contact, or initiate a circuit, between...

 technology based on MIL-STD-188-141A and MIL-STD-188-141B for automated connectivity and frequency selection, along with the high costs of satellite usage, have led to a renaissance in HF usage among these communities. The development of higher speed modems such as those conforming to MIL-STD-188-110B which support data rates up to 9600 bit/s has also increased the usability of HF for data communications. Other standards development such as STANAG
STANAG
STANAG is the NATO abbreviation for Standardization Agreement, which sets up processes, procedures, terms, and conditions for common military or technical procedures or equipment between the member countries of the alliance. Each NATO state ratifies a STANAG and implements it within their own...

 5066 provides for error free data communications through the use of ARQ protocols.

CB radios
Citizens' band radio
Citizens' Band radio is, in many countries, a system of short-distance radio communications between individuals on a selection of 40 channels within the 27-MHz band. Citizens' Band is distinct from the FRS, GMRS, MURS and amateur radio...

 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
Continuous wave
A continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency; and in mathematical analysis, of infinite duration. Continuous wave is also the name given to an early method of radio transmission, in which a carrier wave is switched on and off...

 morse code
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...

 transmissions (especially by amateur radio
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...

 operators) and single sideband
Single-sideband modulation
Single-sideband modulation or Single-sideband suppressed-carrier is a refinement of amplitude modulation that more efficiently uses electrical power and bandwidth....

 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
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....

 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
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

 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.

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

See also

  • High Frequency Active Auroral Research Program
    High Frequency Active Auroral Research Program
    The High Frequency Active Auroral Research Program is an ionospheric research program jointly funded by the U.S. Air Force, the U.S. Navy, the University of Alaska, and the Defense Advanced Research Projects Agency ....

  • High Frequency Internet Protocol
    High Frequency Internet Protocol
    High Frequency Internet Protocolacronyms: HFIP or HF-IP.Usually associated with Automatic Link Establishment and HF radio data communications.HFIP provides protocol layers enabling internet file transfer, chat, web, or email....

  • Low frequency
    Low frequency
    Low frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...

  • Radio propagation
    Radio propagation
    Radio propagation is the behavior of radio waves when they are transmitted, or propagated from one point on the Earth to another, or into various parts of the atmosphere...

  • Space weather
    Space weather
    Space weather is the concept of changing environmental conditions in near-Earth space or thespace from the Sun's atmosphere to the Earth's atmosphere. It is distinct from the concept ofweather within the Earth's planetary atmosphere...


Further reading

  • 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