In radio systems, a biconical antenna is a broad-bandwidth antenna made of two conical conductive objects, nearly touching at their points. Biconical antennas are broadband dipole antennas exhibiting a bandwidth of three octaves or more. A common subtype is the bowtie antenna a two-dimensional version of the biconial design, used for short-range UHF television reception; these are sometimes referred to as butterfly antennas. The biconical antenna has a broad bandwidth. For an infinite antenna, the characteristic impedance at the point of connection is a function of the cone angle only and is independent of the frequency. Practical antennas have a definite resonant frequency. A simple conical monopole antenna is a wire approximation of the solid biconical antenna and has increased bandwidth. Biconical antennas are used in electromagnetic interference testing either for immunity testing, or emissions testing. While the bicon is broadband, it exhibits poor transmitting efficiency at frequencies at the low end of its range, resulting in low field strengths when compared to the input power.
Log periodic dipole arrays, Yagi-Uda antennas, reverberation chambers have shown to achieve much higher field strengths for the power input than a simple biconical antenna in an anechoic chamber. However, when the goal is to characterize a modulated or impulse signal, rather than measuring peak and average spectrum energy content, a reverberation chamber is a poor choice for a test environment. Discone antenna Antenna Radio Television Electromagnetic reverberation chamber Electromagnetic compatibility Antenna-Theory.com Bow Tie Antenna Page UHF Discone Antenna The Discone Antenna Home made video Com-Power Corporation Biconical Antennaa - Broadband antenna suitable for EMC testing
A mobile phone, cell phone, cellphone, or hand phone, sometimes shortened to mobile, cell or just phone, is a portable telephone that can make and receive calls over a radio frequency link while the user is moving within a telephone service area. The radio frequency link establishes a connection to the switching systems of a mobile phone operator, which provides access to the public switched telephone network. Modern mobile telephone services use a cellular network architecture, therefore, mobile telephones are called cellular telephones or cell phones, in North America. In addition to telephony, 2000s-era mobile phones support a variety of other services, such as text messaging, MMS, Internet access, short-range wireless communications, business applications, video games, digital photography. Mobile phones offering only those capabilities are known as feature phones; the first handheld mobile phone was demonstrated by John F. Mitchell and Martin Cooper of Motorola in 1973, using a handset weighing c. 2 kilograms.
In 1979, Nippon Telegraph and Telephone launched the world's first cellular network in Japan. In 1983, the DynaTAC 8000x was the first commercially available handheld mobile phone. From 1983 to 2014, worldwide mobile phone subscriptions grew to over seven billion—enough to provide one for every person on Earth. In first quarter of 2016, the top smartphone developers worldwide were Samsung and Huawei, smartphone sales represented 78 percent of total mobile phone sales. For feature phones as of 2016, the largest were Samsung and Alcatel. A handheld mobile radio telephone service was envisioned in the early stages of radio engineering. In 1917, Finnish inventor Eric Tigerstedt filed a patent for a "pocket-size folding telephone with a thin carbon microphone". Early predecessors of cellular phones included analog radio communications from trains; the race to create portable telephone devices began after World War II, with developments taking place in many countries. The advances in mobile telephony have been traced in successive "generations", starting with the early zeroth-generation services, such as Bell System's Mobile Telephone Service and its successor, the Improved Mobile Telephone Service.
These 0G systems were not cellular, supported few simultaneous calls, were expensive. The first handheld cellular mobile phone was demonstrated by John F. Mitchell and Martin Cooper of Motorola in 1973, using a handset weighing 2 kilograms; the first commercial automated cellular network analog was launched in Japan by Nippon Telegraph and Telephone in 1979. This was followed in 1981 by the simultaneous launch of the Nordic Mobile Telephone system in Denmark, Finland and Sweden. Several other countries followed in the early to mid-1980s; these first-generation systems could support far more simultaneous calls but still used analog cellular technology. In 1983, the DynaTAC 8000x was the first commercially available handheld mobile phone. In 1991, the second-generation digital cellular technology was launched in Finland by Radiolinja on the GSM standard; this sparked competition in the sector as the new operators challenged the incumbent 1G network operators. Ten years in 2001, the third generation was launched in Japan by NTT DoCoMo on the WCDMA standard.
This was followed by 3.5G, 3G+ or turbo 3G enhancements based on the high-speed packet access family, allowing UMTS networks to have higher data transfer speeds and capacity. By 2009, it had become clear that, at some point, 3G networks would be overwhelmed by the growth of bandwidth-intensive applications, such as streaming media; the industry began looking to data-optimized fourth-generation technologies, with the promise of speed improvements up to ten-fold over existing 3G technologies. The first two commercially available technologies billed as 4G were the WiMAX standard, offered in North America by Sprint, the LTE standard, first offered in Scandinavia by TeliaSonera. 5G is a technology and term used in research papers and projects to denote the next major phase in mobile telecommunication standards beyond the 4G/IMT-Advanced standards. The term 5G is not used in any specification or official document yet made public by telecommunication companies or standardization bodies such as 3GPP, WiMAX Forum or ITU-R.
New standards beyond 4G are being developed by standardization bodies, but they are at this time seen as under the 4G umbrella, not for a new mobile generation. Smartphones have a number of distinguishing features; the International Telecommunication Union measures those with Internet connection, which it calls Active Mobile-Broadband subscriptions. In the developed world, smartphones have now overtaken the usage of earlier mobile systems. However, in the developing world, they account for around 50% of mobile telephony. Feature phone is a term used as a retronym to describe mobile phones which are limited in capabilities in contrast to a modern smartphone. Feature phones provide voice calling and text messaging functionality, in addition to basic multimedia and Internet capabilities, other services offered by the user's wireless service provider. A feature phone has additional functions over and above a basic mobile phone, only capable of voice calling and text messaging. Feature phones and basic mobile phones tend to use a proprietary, custom-designed software and user interface.
By contrast, smartphones use a mobile operating system that shares common traits across devices. There are Orthodox Jewish religious re
FM broadcasting is a method of radio broadcasting using frequency modulation technology. Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to provide high-fidelity sound over broadcast radio. FM broadcasting is capable of better sound quality than AM broadcasting, the chief competing radio broadcasting technology, so it is used for most music broadcasts. Theoretically wideband AM can offer good sound quality, provided the reception conditions are ideal. FM radio stations use the VHF frequencies; the term "FM band" describes the frequency band in a given country, dedicated to FM broadcasting. Throughout the world, the FM broadcast band falls within the VHF part of the radio spectrum. 87.5 to 108.0 MHz is used, or some portion thereof, with few exceptions: In the former Soviet republics, some former Eastern Bloc countries, the older 65.8–74 MHz band is used. Assigned frequencies are at intervals of 30 kHz; this band, sometimes referred to as the OIRT band, is being phased out in many countries.
In those countries the 87.5–108.0 MHz band is referred to as the CCIR band. In Japan, the band 76–95 MHz is used; the frequency of an FM broadcast station is an exact multiple of 100 kHz. In most of South Korea, the Americas, the Philippines and the Caribbean, only odd multiples are used. In some parts of Europe and Africa, only multiples are used. In the UK odd or are used. In Italy, multiples of 50 kHz are used. In most countries the maximum permitted frequency error is specified, the unmodulated carrier should be within 2000 Hz of the assigned frequency. There are other unusual and obsolete FM broadcasting standards in some countries, including 1, 10, 30, 74, 500, 300 kHz. However, to minimise inter-channel interference, stations operating from the same or geographically close transmitter sites tend to keep to at least a 500 kHz frequency separation when closer frequency spacing is technically permitted, with closer tunings reserved for more distantly spaced transmitters, as interfering signals are more attenuated and so have less effect on neighboring frequencies.
Frequency modulation or FM is a form of modulation which conveys information by varying the frequency of a carrier wave. With FM, frequency deviation from the assigned carrier frequency at any instant is directly proportional to the amplitude of the input signal, determining the instantaneous frequency of the transmitted signal; because transmitted FM signals use more bandwidth than AM signals, this form of modulation is used with the higher frequencies used by TV, the FM broadcast band, land mobile radio systems. The maximum frequency deviation of the carrier is specified and regulated by the licensing authorities in each country. For a stereo broadcast, the maximum permitted carrier deviation is invariably ±75 kHz, although a little higher is permitted in the United States when SCA systems are used. For a monophonic broadcast, again the most common permitted. However, some countries specify a lower value for monophonic broadcasts, such as ±50 kHz. Random noise has a triangular spectral distribution in an FM system, with the effect that noise occurs predominantly at the highest audio frequencies within the baseband.
This can be offset, to a limited extent, by boosting the high frequencies before transmission and reducing them by a corresponding amount in the receiver. Reducing the high audio frequencies in the receiver reduces the high-frequency noise; these processes of boosting and reducing certain frequencies are known as pre-emphasis and de-emphasis, respectively. The amount of pre-emphasis and de-emphasis used is defined by the time constant of a simple RC filter circuit. In most of the world a 50 µs time constant is used. In the Americas and South Korea, 75 µs is used; this applies to both stereo transmissions. For stereo, pre-emphasis is applied to the left and right channels before multiplexing; the use of pre-emphasis becomes a problem because of the fact that many forms of contemporary music contain more high-frequency energy than the musical styles which prevailed at the birth of FM broadcasting. Pre-emphasizing these high frequency sounds would cause excessive deviation of the FM carrier. Modulation control devices are used to prevent this.
Systems more modern than FM broadcasting tend to use either programme-dependent variable pre-emphasis. Long before FM stereo transmission was considered, FM multiplexing of other types of audio level information was experimented with. Edwin Armstrong who invented FM was the first to experiment with multiplexing, at his experimental 41 MHz station W2XDG located on the 85th floor of the Empire State Building in New York City; these FM multiplex transmissions started in November 1934 and consisted of the main channel audio program and three subcarriers: a fax program, a synchronizing signal for the fax program and a telegraph “order” channel. These original FM multiplex subcarriers were amplitude modulated. Two musical programs, consisting of both the Red and Blue Network program feeds of the NBC Radio Network, were transmitted using the same system of subcarrier modulation as part of a studio-to-transmitter link system. In April 1935, the AM subcarriers were replaced with much improved results.
The first FM subcarrier transmissions emanating from Major Armstrong's experimental station KE2XCC at Alpine, New Jersey occurred in 1948. These transmissions consisted of two-cha
A halo antenna, or halo, is a horizontally polarized, omnidirectional 1⁄2 wavelength dipole antenna, bent into a loop with a small break on the side of the loop directly opposite the feed point. The dipole ends are close but do not meet, may have an air capacitor between them as needed to establish resonance. Early halo antennas used two or more parallel loops, modeled after a 1943 patent, a folded dipole bent into a circle; the two loop design helps with impedance matching. More recent halo antennas have tended to use a single conductor fed with a gamma match; the newer approach uses less material and reduces wind load, but may be less mechanically robust, more narrow-banded, requires a balun to prevent feed-line radiation. The gamma match is not an essential feature, however: There are other, uncommon methods of feeding halos. A halo antenna is distinct from a full-wave loop, double its size or larger, whose element is a complete loop, with no breaks. Further, full-wave loops radiate predominantly perpendicular to the plane of the loop at their lowest frequency, whereas halos radiate in the loop plane, with some radiation in the perpendicular direction.
A halo antenna is distinct from the small-loop antenna in size, radiation pattern, radiation resistance, or efficiency. Halos are customarily operated with the plane of the loop oriented horizontally, parallel to the ground, whereas small-loop antennas are oriented vertically. A small-loop antenna designed for transmitting is is about 1⁄4 wave – half the size of a halo built for the same frequency – or a bit smaller. A small-loop can be at most a little less than 1⁄3 wave in circumference, or 2⁄3 of the size of a halo, becomes difficult to tune as it approaches that maximum; the current profile of a small loop is uniform or nearly so, whereas the current on the halo antenna is sinusoidal. All of the current in a halo antenna is on the side opposite the break in the loop, also the loop's feed-point; the part of the halo near the split has high voltages, but carries no current and produces no radiation. The part opposite that gap is the part that radiates, tends to radiate more towards the split in the loop.
Because a 1⁄4 wave small loop has the the same current flowing in the entire loop it radiates in the plane of the loop uniformly, with no preferred direction in that plane. Unlike full-wave loops, halo antennas do not produce much radiation perpendicular to the plane of the loop but do produce some. Full wave loops produce their highest radiation perpendicular to the loop and none in the plane of the loop. Small loops are the opposite: They produce their greatest radiation in the plane of the loop, none in the perpendicular direction. Halo antennas’ radiation pattern, like their size, falls inbetween large and small loops, although somewhat closer to small loops. Since antenna size is measured in multiples of wavelengths, a halo antenna with sufficient capacitance to operate at half its design frequency will function as a small loop. In that sense – though built to deal with different practical constraints – the two types of loop antenna are nearly identical; the only two issues are how well the loop + impedance matching system + radio can accommodate the reactance at a frequency the antenna was not designed for whether the capacitance across the halo’s gap is enough to allow a near-continuous current around the loop at below-design frequencies.
When constructed the antenna will present a good match to 50 Ohm coaxial cable with a low SWR. Towards the horizon, the pattern is less. Making the loop smaller and adding more capacity between the element tips evens out the gain while reducing upward radiation; the radiating element of the halo is grounded, which tends to reduce static buildup, an advantage shared by many antennas fed with a gamma match. On the VHF bands and above, the physical diameter of a halo is small enough to be used as a mobile antenna. Halos may be stacked for additional gain; this reduces the high angle radiation, but has little or no effect on the shape of the radiation pattern in the plane of the antenna. High angle radiation is not useful for VHF work except for space communications. Halos pick up less ignition noise from vehicles. Halo antennas have lower voltages across their gaps than small-loop antennas fed with the same power, reducing problems with arcing and electric shock, radiate more efficiently than small loops.
Radiation from horizontal halos has no vertical component. One can expect 3 -- 20 dB of signal loss. For mobile use, the halo is rather conspicuous compared to the much more common vertical whip antenna, may attract unwanted attention; the halo is a rigid structure and may suffer damage from tree branches or other obstacles in mobile operation. A halo antenna can function as designed – as a resonant half-wave antenna – only at one frequency, limiting its use to a single band, or only a part of one band. A small transmitting loop can be re-tuned to a range of frequencies wider than 2:1, approaching 3:1, which can cover two or three different amateur bands. A halo antenna is not as efficient for distance contacts via skywave as a horizontal small loop, other things being equal, since more of its signal is sent upward instead of outward, wasting signal power
Speed of light
The speed of light in vacuum denoted c, is a universal physical constant important in many areas of physics. Its exact value is 299,792,458 metres per second, it is exact because by international agreement a metre is defined as the length of the path travelled by light in vacuum during a time interval of 1/299792458 second. According to special relativity, c is the maximum speed at which all conventional matter and hence all known forms of information in the universe can travel. Though this speed is most associated with light, it is in fact the speed at which all massless particles and changes of the associated fields travel in vacuum; such particles and waves travel at c regardless of the motion of the source or the inertial reference frame of the observer. In the special and general theories of relativity, c interrelates space and time, appears in the famous equation of mass–energy equivalence E = mc2; the speed at which light propagates through transparent materials, such as glass or air, is less than c.
The ratio between c and the speed v at which light travels in a material is called the refractive index n of the material. For example, for visible light the refractive index of glass is around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200,000 km/s. For many practical purposes and other electromagnetic waves will appear to propagate instantaneously, but for long distances and sensitive measurements, their finite speed has noticeable effects. In communicating with distant space probes, it can take minutes to hours for a message to get from Earth to the spacecraft, or vice versa; the light seen from stars left them many years ago, allowing the study of the history of the universe by looking at distant objects. The finite speed of light limits the theoretical maximum speed of computers, since information must be sent within the computer from chip to chip; the speed of light can be used with time of flight measurements to measure large distances to high precision. Ole Rømer first demonstrated in 1676 that light travels at a finite speed by studying the apparent motion of Jupiter's moon Io.
In 1865, James Clerk Maxwell proposed that light was an electromagnetic wave, therefore travelled at the speed c appearing in his theory of electromagnetism. In 1905, Albert Einstein postulated that the speed of light c with respect to any inertial frame is a constant and is independent of the motion of the light source, he explored the consequences of that postulate by deriving the theory of relativity and in doing so showed that the parameter c had relevance outside of the context of light and electromagnetism. After centuries of precise measurements, in 1975 the speed of light was known to be 299792458 m/s with a measurement uncertainty of 4 parts per billion. In 1983, the metre was redefined in the International System of Units as the distance travelled by light in vacuum in 1/299792458 of a second; the speed of light in vacuum is denoted by a lowercase c, for "constant" or the Latin celeritas. In 1856, Wilhelm Eduard Weber and Rudolf Kohlrausch had used c for a different constant shown to equal √2 times the speed of light in vacuum.
The symbol V was used as an alternative symbol for the speed of light, introduced by James Clerk Maxwell in 1865. In 1894, Paul Drude redefined c with its modern meaning. Einstein used V in his original German-language papers on special relativity in 1905, but in 1907 he switched to c, which by had become the standard symbol for the speed of light. Sometimes c is used for the speed of waves in any material medium, c0 for the speed of light in vacuum; this subscripted notation, endorsed in official SI literature, has the same form as other related constants: namely, μ0 for the vacuum permeability or magnetic constant, ε0 for the vacuum permittivity or electric constant, Z0 for the impedance of free space. This article uses c for the speed of light in vacuum. Since 1983, the metre has been defined in the International System of Units as the distance light travels in vacuum in 1⁄299792458 of a second; this definition fixes the speed of light in vacuum at 299,792,458 m/s. As a dimensional physical constant, the numerical value of c is different for different unit systems.
In branches of physics in which c appears such as in relativity, it is common to use systems of natural units of measurement or the geometrized unit system where c = 1. Using these units, c does not appear explicitly because multiplication or division by 1 does not affect the result; the speed at which light waves propagate in vacuum is independent both of the motion of the wave source and of the inertial frame of reference of the observer. This invariance of the speed of light was postulated by Einstein in 1905, after being motivated by Maxwell's theory of electromagnetism and the lack of evidence for the luminiferous aether, it is only possible to verify experimentally that the two-way speed of light is frame-independent, because it is impossible to measure the one-way speed of light without some convention as to how clocks at the source and at the detector should be synchronized. However
Global Positioning System
The Global Positioning System Navstar GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Air Force. It is a global navigation satellite system that provides geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. Obstacles such as mountains and buildings block the weak GPS signals; the GPS does not require the user to transmit any data, it operates independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the GPS positioning information. The GPS provides critical positioning capabilities to military and commercial users around the world; the United States government created the system, maintains it, makes it accessible to anyone with a GPS receiver. The GPS project was launched by the U. S. Department of Defense in 1973 for use by the United States military and became operational in 1995.
It was allowed for civilian use in the 1980s. Advances in technology and new demands on the existing system have now led to efforts to modernize the GPS and implement the next generation of GPS Block IIIA satellites and Next Generation Operational Control System. Announcements from Vice President Al Gore and the White House in 1998 initiated these changes. In 2000, the U. S. Congress authorized the modernization effort, GPS III. During the 1990s, GPS quality was degraded by the United States government in a program called "Selective Availability"; the GPS system is provided by the United States government, which can selectively deny access to the system, as happened to the Indian military in 1999 during the Kargil War, or degrade the service at any time. As a result, several countries have developed or are in the process of setting up other global or regional satellite navigation systems; the Russian Global Navigation Satellite System was developed contemporaneously with GPS, but suffered from incomplete coverage of the globe until the mid-2000s.
GLONASS can be added to GPS devices, making more satellites available and enabling positions to be fixed more and to within two meters. China's BeiDou Navigation Satellite System is due to achieve global reach in 2020. There are the European Union Galileo positioning system, India's NAVIC. Japan's Quasi-Zenith Satellite System is a GPS satellite-based augmentation system to enhance GPS's accuracy; when selective availability was lifted in 2000, GPS had about a five-meter accuracy. The latest stage of accuracy enhancement uses the L5 band and is now deployed. GPS receivers released in 2018 that use the L5 band can have much higher accuracy, pinpointing to within 30 centimetres or 11.8 inches. The GPS project was launched in the United States in 1973 to overcome the limitations of previous navigation systems, integrating ideas from several predecessors, including classified engineering design studies from the 1960s; the U. S. Department of Defense developed the system, which used 24 satellites, it was developed for use by the United States military and became operational in 1995.
Civilian use was allowed from the 1980s. Roger L. Easton of the Naval Research Laboratory, Ivan A. Getting of The Aerospace Corporation, Bradford Parkinson of the Applied Physics Laboratory are credited with inventing it; the work of Gladys West is credited as instrumental in the development of computational techniques for detecting satellite positions with the precision needed for GPS. The design of GPS is based on similar ground-based radio-navigation systems, such as LORAN and the Decca Navigator, developed in the early 1940s. Friedwardt Winterberg proposed a test of general relativity – detecting time slowing in a strong gravitational field using accurate atomic clocks placed in orbit inside artificial satellites. Special and general relativity predict that the clocks on the GPS satellites would be seen by the Earth's observers to run 38 microseconds faster per day than the clocks on the Earth; the GPS calculated positions would drift into error, accumulating to 10 kilometers per day. This was corrected for in the design of GPS.
Winterberg, Friedwardt. “Relativistische Zeitdilatation eines künstlichen Satelliten ” When the Soviet Union launched the first artificial satellite in 1957, two American physicists, William Guier and George Weiffenbach, at Johns Hopkins University's Applied Physics Laboratory decided to monitor its radio transmissions. Within hours they realized that, because of the Doppler effect, they could pinpoint where the satellite was along its orbit; the Director of the APL gave them access to their UNIVAC to do the heavy calculations required. Early the next year, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem—pinpointing the user's location, given that of the satellite; this led them and APL to develop the TRANSIT system. In 1959, ARPA played a role in TRANSIT. TRANSIT was first tested in 1960, it used a constellation of five satellites and could provide a navigational fix once per hour. In 1967, the U. S. Navy developed the Timation satellite, which proved the feasibility of placing accurate clocks in space, a technology required for GPS.
In the 1970s, the ground-based OMEGA navigation system, based on phase comparison of signal transmission from pairs of stations
A batwing or super turnstile antenna is a type of broadcasting antenna used at VHF and UHF frequencies, named for its distinctive shape which resembles a bat wing or bow tie. Stacked arrays of batwing antennas are used as television broadcasting antennas due to their omnidirectional characteristics. Batwing antennas generate a horizontally polarized signal; the advantage of the "batwing" design for television broadcasting is. It was the first used television broadcasting antenna. Batwing antennas are a specialized type of crossed dipole antenna, a variant of the turnstile antenna. Two pairs of identical vertical batwing-shaped elements are mounted at right angles around a common mast. Element “wings” on opposite sides are fed as a dipole. To generate an omnidirectional pattern, the two dipoles are fed 90° out of phase; the antenna radiates horizontally polarized radiation in the horizontal plane. Each group of four elements at a single level is referred to as a bay; the radiation pattern is close to omnidirectional but has four small lobes in the directions of the four elements.
To reduce power radiated in the unwanted axial directions, in broadcast applications multiple bays fed in phase are stacked vertically with a spacing of one wavelength, to create a collinear array. This generates an omnidirectional radiation pattern with increased horizontal gain, suitable for terrestrial broadcasting; the "batwing" shape of the elements is used because it gives the antenna a wide bandwidth of 20% of operating frequency at a VSWR of 1.1:1. This makes the antenna design suitable for broadcasters who wish to use a single antenna to transmit multiple television signals and thus made the batwing the preferred antenna for lowband TV stations in the early days of broadcast television. Turnstile antenna Y. T. Lo and S. W. Lee "Antenna Handbook" Vol III: Antenna Applications. ISBN V10 0442015941 / ISDN V13 978-0442015947 Markley, Don. "Television antenna systems."'Broadcast Engineering.' 1 Apr 2004. Milligan, Thomas A.'Modern antenna design.' Wiley-IEEE Press, 2005. ISBN 978-0-471-45776-3 Sclater, Neil.'Electronics technology handbook.'
McGraw-Hill Professional, 1999. ISBN 0-07-058048-0