- High frequency
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). Shortwave(2.310 - 25.820 MHz) overlaps and is slightly lower than HF.
ionosphereoften reflects HF radio waves quite well (a phenomenon known as skywave propagation), 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
Maximum usable frequency
Lowest usable high frequency
*Frequency of operation within the HF range
The high frequency band is very popular with
amateur radiooperators, who can take advantage of direct, long-distance (often inter-continental) communications and the "thrill factor" resulting from making contacts in variable conditions. International shortwavebroadcasting 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-188-141A 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 STANAG5066 provides for error free data communications through the use of ARQprotocols.
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 codetransmissions (especially by amateur radiooperators) 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 spectrumspace.
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)
Internetaccess, 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).
High Frequency Internet Protocol
High Frequency Active Auroral Research Program
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* Tomislav Stimac, " [http://www.vlf.it/frequency/bands.html Definition of frequency bands (VLF, ELF... etc.)] ". IK1QFK Home Page (vlf.it).
* Douglas C. Smith, [http://www.emcesd.com/ High Frequency Measurements Web Page; Index and Technical Tidbits] . D. C. Smith Consultants, Los Gatos, CA.
* [http://www.its.bldrdoc.gov/elbert/hf.html High Frequency Propagation Models] , its.bldrdoc.gov.
* [http://www.cscamm.umd.edu/programs/hfw05/ High Frequency Wave Propagation] , cscamm.umd.edu.
* " [http://www.analog.com/UploadedFiles/Application_Notes/698455131755584673020828AN_345.pdf Grounding for Low- and High-Frequency Circuits] " (PDF)
* " [http://www.mrec.org/pubs/HighFrequencyNoise_InformationalPage_05.pdf High frequency noise] " (PDF)
* " [http://www.codan.com.au/HFRadio/WhyHF/tabid/305/Default.aspx Advantages of HF Radio] " Codan
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