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T2FD
The ''Tilted Terminated Folded Dipole'' (T²FD, T2FD, or TTFD) or ''Balanced Termination, Folded Dipole'' (BTFD) - also known as W3HH antenna - is a general-purpose shortwave antenna developed in the late 1940s by the United States Navy. It performs reasonably well over a broad frequency range, without marked dead spots in terms of either frequency, direction, or angle of radiation above the horizon. Although inferior in terms of efficiency (at least 30% of the RF power is lost as heat in the resistor ) to antennas specifically designed for given frequency bands, or optimized for directionality, its all-around performance, relatively modest size, low cost, and the fact that it does not require any complicated matching to operate with a standard shortwave transmitter, have made it popular in professional shortwave communications where ERP or gain are not a concern. One example would be clear channel low power HF communications. History The history of the T²FD antenna divides ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dipole Antenna
In radio and telecommunications a dipole antenna or doublet is the simplest and most widely used class of antenna. The dipole is any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole with a radiating structure supporting a line current so energized that the current has only one node at each end. A dipole antenna commonly consists of two identical conductive elements such as metal wires or rods. The driving current from the transmitter is applied, or for receiving antennas the output signal to the receiver is taken, between the two halves of the antenna. Each side of the feedline to the transmitter or receiver is connected to one of the conductors. This contrasts with a monopole antenna, which consists of a single rod or conductor with one side of the feedline connected to it, and the other side connected to some type of ground. A common example of a dipole is the "rabbit ears" television antenna found on broadcast te ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shortwave Broadband Antenna
A shortwave broadband antenna is a radio antenna that can be used for transmission (and reception) of any shortwave radio band from among the greater part of the shortwave radio spectrum, without requiring any band-by-band adjustment of the antenna. Generally speaking, there is no difficulty in building an adequate receiving antenna; the challenge is designing an antenna which can be used for transmission without an adjustable impedance matching network. An ideal “broadband” shortwave antenna would work continuously across much of, if not all of, the shortwave spectrum with good radiation efficiency and minimal compromise of the radiation pattern. Most practical broadband antennas compromise on one of the above: Either they only work on a few relatively narrow slices of the HF radio spectrum, or they work across the complete spectrum, without gaps, but are inefficient radiators on some or all of the frequencies. Other antennas provide adequate efficiency on some frequencies, but ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
T2FD Antenna--highlighted Components
T, or t, is the twentieth letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''tee'' (pronounced ), plural ''tees''. It is derived from the Semitic Taw 𐤕 of the Phoenician and Paleo-Hebrew script (Aramaic and Hebrew Taw ת/𐡕/, Syriac Taw ܬ, and Arabic ت Tāʼ) via the Greek letter τ (tau). In English, it is most commonly used to represent the voiceless alveolar plosive, a sound it also denotes in the International Phonetic Alphabet. It is the most commonly used consonant and the second most commonly used letter in English-language texts. History ''Taw'' was the last letter of the Western Semitic and Hebrew alphabets. The sound value of Semitic ''Taw'', Greek alphabet Tαυ (''Tau''), Old Italic and Latin T has remained fairly constant, representing in each of these; and it has also kept its original basic shape in most of these alphabets. Use in w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reactance (electronics)
In electrical circuits, reactance is the opposition presented to alternating current by inductance or capacitance. Greater reactance gives smaller current for the same applied voltage. Reactance is similar to resistance in this respect, but does not lead to dissipation of electrical energy as heat; instead, energy is momentarily stored in the reactance, and a quarter-cycle later returned to the circuit. Reactance is used to compute amplitude and phase changes of sinusoidal alternating current going through a circuit element. Like resistance, reactance is measured in ohms, with positive values indicating ''inductive'' reactance and negative indicating ''capacitive'' reactance. It is denoted by the symbol X. An ideal resistor has zero reactance, whereas ideal inductors and capacitors have zero resistance. As frequency increases, inductive reactance increases and capacitive reactance decreases. Comparison to resistance Reactance is similar to resistance in that larger reactan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Standing Wave Ratio
In radio engineering and telecommunications, standing wave ratio (SWR) is a measure of impedance matching of loads to the characteristic impedance of a transmission line or waveguide. Impedance mismatches result in standing waves along the transmission line, and SWR is defined as the ratio of the partial standing wave's amplitude at an antinode (maximum) to the amplitude at a node (minimum) along the line. The SWR is usually thought of in terms of the maximum and minimum AC voltages along the transmission line, thus called the voltage standing wave ratio or VSWR (sometimes pronounced "vizwar" ). For example, the VSWR value 1.2:1 means that an AC voltage, due to standing waves along the transmission line, will have a peak value 1.2 times that of the minimum AC voltage along that line, if the line is at least one half wavelength long. The SWR can be also defined as the ratio of the maximum amplitude to minimum amplitude of the transmission line's currents, electric field s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Decibel
The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a power ratio of 101/10 (approximately ) or root-power ratio of 10 (approximately ). The unit expresses a relative change or an absolute value. In the latter case, the numeric value expresses the ratio of a value to a fixed reference value; when used in this way, the unit symbol is often suffixed with letter codes that indicate the reference value. For example, for the reference value of 1 volt, a common suffix is " V" (e.g., "20 dBV"). Two principal types of scaling of the decibel are in common use. When expressing a power ratio, it is defined as ten times the logarithm in base 10. That is, a change in ''power'' by a factor of 10 corresponds to a 10 dB change in level. When expressing root-power quantities, a change in ''ampl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Belrose
John S. (Jack) Belrose (born 24 November 1926), is a Canadian radio scientist. He was born in the small town of Warner, Alberta. He attended the University of Cambridge, where he was awarded a PhD in 1958. He has worked for the Defence Research Telecommunications Establishment (DRTE) for 33 years. He is a member of the Canadian Amateur Radio Hall of Fame and, along with Walter Cronkite Walter Leland Cronkite Jr. (November 4, 1916 – July 17, 2009) was an American broadcast journalist who served as anchorman for the ''CBS Evening News'' for 19 years (1962–1981). During the 1960s and 1970s, he was often cited as "the mo ..., was awarded the Radio Club of America's Armstrong Medal on 16 November 2007. References External linksRemembrances of a Radio Scientist- Belrose's report on his 50th anniversary of working in the field of radio science.- a paper by Jack Belrose. 1926 births Possibly living people Canadian engineers Alumni of the University of Cambridge Ca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shortwave
Shortwave radio is radio transmission using shortwave (SW) radio frequencies. There is no official definition of the band, but the range always includes all of the high frequency band (HF), which extends from 3 to 30 MHz (100 to 10 metres); above the medium frequency band (MF), to the bottom of the VHF band. Radio waves in the shortwave band can be reflected or refracted from a layer of electrically charged atoms in the atmosphere called the ionosphere. Therefore, short waves directed at an angle into the sky can be reflected back to Earth at great distances, beyond the horizon. This is called skywave or "skip" propagation. Thus shortwave radio can be used for communication over very long distances, in contrast to radio waves of higher frequency, which travel in straight lines (line-of-sight propagation) and are limited by the visual horizon, about 64 km (40 miles). Shortwave broadcasts of radio programs played an important role in the early days of rad ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Construction
Construction is a general term meaning the art and science of forming Physical object, objects, systems, or organizations."Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 It comes from the Latin word ''constructio'' (from ''com-'' "together" and ''struere'' "to pile up") and Old French ''construction''. To 'construct' is a verb: the act of building, and the noun is construction: how something is built or the nature of its structure. In its most widely used context, construction covers the processes involved in delivering buildings, infrastructure, industrial facilities, and associated activities through to the end of their life. It typically starts with planning, financing, and design that continues until the asset is built and ready for use. Construction also covers repairs and maintenance work, any works to expand, extend and improve the asset, and its eventual demolition, dismantling or wikt:de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Standing Wave Ratio
In radio engineering and telecommunications, standing wave ratio (SWR) is a measure of impedance matching of loads to the characteristic impedance of a transmission line or waveguide. Impedance mismatches result in standing waves along the transmission line, and SWR is defined as the ratio of the partial standing wave's amplitude at an antinode (maximum) to the amplitude at a node (minimum) along the line. The SWR is usually thought of in terms of the maximum and minimum AC voltages along the transmission line, thus called the voltage standing wave ratio or VSWR (sometimes pronounced "vizwar" ). For example, the VSWR value 1.2:1 means that an AC voltage, due to standing waves along the transmission line, will have a peak value 1.2 times that of the minimum AC voltage along that line, if the line is at least one half wavelength long. The SWR can be also defined as the ratio of the maximum amplitude to minimum amplitude of the transmission line's currents, electric field s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Omnidirectional Antenna
In radio communication, an omnidirectional antenna is a class of antenna which radiates equal radio power in all directions perpendicular to an axis (azimuthal directions), with power varying with angle to the axis ( elevation angle), declining to zero on the axis. When graphed in three dimensions ''(see graph)'' this radiation pattern is often described as ''doughnut-shaped''. Note that this is different from an isotropic antenna, which radiates equal power in ''all'' directions, having a ''spherical'' radiation pattern. Omnidirectional antennas oriented vertically are widely used for nondirectional antennas on the surface of the Earth because they radiate equally in all horizontal directions, while the power radiated drops off with elevation angle so little radio energy is aimed into the sky or down toward the earth and wasted. Omnidirectional antennas are widely used for radio broadcasting antennas, and in mobile devices that use radio such as cell phones, FM radios, w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Watt (unit)
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Watt (1736–1819), an 18th-century Scottish inventor, mechanical engineer, and chemist who improved the Newcomen engine with his own steam engine in 1776. Watt's invention was fundamental for the Industrial Revolution. Overview When an object's velocity is held constant at one metre per second against a constant opposing force of one newton, the rate at which work is done is one watt. : \mathrm In terms of electromagnetism, one watt is the rate at which electrical work is performed when a current of one ampere (A) flows across an electrical potential difference of one volt (V), meaning the watt is equivalent to the volt-ampere (the latter unit, however, is used for a different quantity from the real power of an electrical circuit). : \ma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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