The BNC connector is a miniature quick connect/disconnect radio frequency connector used for coaxial cable. The interface specifications for the BNC and many other connectors are referenced in MIL-STD-348, it features two bayonet lugs on the female connector. BNC connectors are used with miniature-to-subminiature coaxial cable in radio and other radio-frequency electronic equipment, test instruments, video signals; the BNC was used for early computer networks, including ARCnet, the IBM PC Network, the 10BASE2 variant of Ethernet. BNC connectors are made to match the characteristic impedance of cable at either 75 ohms, they are applied for frequencies below 4 GHz and voltages below 500 volts. Similar connectors using the bayonet connection principle exist, a threaded connector is available. United States military standard MIL-PRF-39012 entitled Connectors, Radio Frequency, General Specification for covers the general requirements and tests for radio frequency connectors used with flexible cables and certain other types of coaxial transmission lines in military and spaceflight applications.
The BNC was designed for military use and has gained wide acceptance in video and RF applications to 2 GHz. The BNC uses some plastic dielectric on each gender connector; this dielectric causes increasing losses at higher frequencies. Above 4 GHz, the slots may radiate signals, so the connector is usable, but not stable up to about 11 GHz. Both 50 ohm and 75 ohm versions are available; the BNC connector is used for signal connections such as: analog and serial digital interface video signals radio antennas aerospace electronics nuclear instrumentation test equipment. The BNC connector is used for composite video on commercial video devices. Consumer electronics devices with RCA connector jacks can be used with BNC-only commercial video equipment by inserting an adapter. BNC connectors were used on 10base2 thin Ethernet network cables and network cards. BNC connections can be found in recording studios. Digital recording equipment uses the connection for synchronization of various components via the transmission of word clock timing signals.
The male connector is fitted to a cable, the female to a panel on equipment. Cable connectors are designed to be fitted by crimping using a special power or manual tool. Wire strippers which strip outer jacket, shield braid, inner dielectric to the correct lengths in one operation are used; the connector was named the BNC after its bayonet mount locking mechanism and its inventors, Paul Neill and Carl Concelman. Neill worked at Bell Labs and invented the N connector. A backronym has been mistakenly applied to it: British Naval Connector. Another common incorrectly attributed; the basis for the development of the BNC connector was the work of Octavio M. Salati, a graduate of the Moore School of Electrical Engineering of the University of Pennsylvania. In 1945, while working at Hazeltine Electronics Corporation, he filed a patent for a connector for coaxial cables that would minimize wave reflection/loss; the patent was granted in 1951. BNC connectors are most made in 50 and 75 ohm versions, matched for use with cables of the same characteristic impedance.
The 75 ohm types can sometimes be recognized by the reduced or absent dielectric in the mating ends but this is by no means reliable. There was a proposal in the early 1970s for the dielectric material to be coloured red in 75 ohm connectors, while this is implemented, it did not become standard; the 75 ohm connector is dimensionally different from the 50 ohm variant, but the two can be made to mate. The 50 ohm connectors are specified for use at frequencies up to 4 GHz and the 75 ohm version up to 2 GHz. A 95 ohm variant is used within the aerospace sector, but elsewhere, it is used with the 95 ohm video connections for glass cockpit displays on some aircraft. Video and DS3 Telco central office applications use 75 ohm BNC connectors, whereas 50 ohm connectors are used for data and RF. Many VHF receivers used 75 ohm antenna inputs, so they used 75 ohm BNC connectors. Reverse-polarity BNC is a variation of the BNC specification which reverses the polarity of the interface. In a connector of this type, the female contact found in a jack is in the plug, while the male contact found in a plug is in the jack.
This ensures that reverse polarity interface connectors do not mate with standard interface connectors. The SHV connector is a high-voltage BNC variant. Smaller versions of the BNC connector, called Mini BNC and High Density BNC, are manufactured by Amphenol. While retaining the electrical characteristics of the original specification, they have smaller footprints giving a higher packing density on circuit boards and equipment backplanes; these connectors have true 75 ohm impedance making them suitable for HD video applications. The different versions are designed to mate with each other, a 75 ohm and a 50 ohm BNC connector which both comply with the 2007 IEC standard, IEC 60169-8, will mate non-destructively. At least one manufacturer claims high reliability for the connectors' compatibility. At frequencies below 10 MHz the impedance mismatch between a 50 ohm connector or cable and a 75 ohm one has negligible effects. BNC connectors were thus made only in 50 ohm
Amateur radio known as ham radio, describes the use of radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport and emergency communication. The term "amateur" is used to specify "a duly authorised person interested in radioelectric practice with a purely personal aim and without pecuniary interest; the amateur radio service is established by the International Telecommunication Union through the Radio Regulations. National governments regulate technical and operational characteristics of transmissions and issue individual stations licenses with an identifying call sign. Prospective amateur operators are tested for their understanding of key concepts in electronics and the host government's radio regulations. Radio amateurs use a variety of voice, text and data communications modes and have access to frequency allocations throughout the RF spectrum; this enables communication across a city, country, the world, or into space.
In many countries, amateur radio operators may send, receive, or relay radio communications between computers or transceivers connected to secure virtual private networks on the Internet. Amateur radio is represented and coordinated by the International Amateur Radio Union, organized in three regions and has as its members the national amateur radio societies which exist in most countries. According to an estimate made in 2011 by the American Radio Relay League, two million people throughout the world are involved with amateur radio. About 830,000 amateur radio stations are located in IARU Region 2 followed by IARU Region 3 with about 750,000 stations. A smaller number, about 400,000, are located in IARU Region 1; the origins of amateur radio can be traced to the late 19th century, but amateur radio as practiced today began in the early 20th century. The First Annual Official Wireless Blue Book of the Wireless Association of America, produced in 1909, contains a list of amateur radio stations.
This radio callbook lists wireless telegraph stations in Canada and the United States, including 89 amateur radio stations. As with radio in general, amateur radio was associated with various amateur experimenters and hobbyists. Amateur radio enthusiasts have contributed to science, engineering and social services. Research by amateur operators has founded new industries, built economies, empowered nations, saved lives in times of emergency. Ham radio can be used in the classroom to teach English, map skills, math and computer skills; the term "ham" was first a pejorative term used in professional wired telegraphy during the 19th century, to mock operators with poor Morse code sending skills. This term continued to be used after the invention of radio and the proliferation of amateur experimentation with wireless telegraphy; the use of "ham" meaning "amateurish or unskilled" survives today in other disciplines. The amateur radio community subsequently began to reclaim the word as a label of pride, by the mid-20th century it had lost its pejorative meaning.
Although not an acronym, it is mistakenly written as "HAM" in capital letters. The many facets of amateur radio attract practitioners with a wide range of interests. Many amateurs begin with a fascination of radio communication and combine other personal interests to make pursuit of the hobby rewarding; some of the focal areas amateurs pursue include radio contesting, radio propagation study, public service communication, technical experimentation, computer networking. Amateur radio operators use various modes of transmission to communicate; the two most common modes for voice transmissions are single sideband. FM offers high quality audio signals, while SSB is better at long distance communication when bandwidth is restricted. Radiotelegraphy using Morse code known as "CW" from "continuous wave", is the wireless extension of landline telegraphy developed by Samuel Morse and dates to the earliest days of radio. Although computer-based modes and methods have replaced CW for commercial and military applications, many amateur radio operators still enjoy using the CW mode—particularly on the shortwave bands and for experimental work, such as earth-moon-earth communication, because of its inherent signal-to-noise ratio advantages.
Morse, using internationally agreed message encodings such as the Q code, enables communication between amateurs who speak different languages. It is popular with homebrewers and in particular with "QRP" or very-low-power enthusiasts, as CW-only transmitters are simpler to construct, the human ear-brain signal processing system can pull weak CW signals out of the noise where voice signals would be inaudible. A similar "legacy" mode popular with home constructors is amplitude modulation, pursued by many vintage amateur radio enthusiasts and aficionados of vacuum tube technology. Demonstrating a proficiency in Morse code was for many years a requirement to obtain an amateur license to transmit on frequencies below 30 MHz. Following changes in international regulations in 2003, countries are no longer required to demand proficiency; the United States Federal
The ohm is the SI derived unit of electrical resistance, named after German physicist Georg Simon Ohm. Although several empirically derived standard units for expressing electrical resistance were developed in connection with early telegraphy practice, the British Association for the Advancement of Science proposed a unit derived from existing units of mass and time and of a convenient size for practical work as early as 1861; the definition of the ohm was revised several times. Today, the definition of the ohm is expressed from the quantum Hall effect; the ohm is defined as an electrical resistance between two points of a conductor when a constant potential difference of one volt, applied to these points, produces in the conductor a current of one ampere, the conductor not being the seat of any electromotive force. Ω = V A = 1 S = W A 2 = V 2 W = s F = H s = J ⋅ s C 2 = kg ⋅ m 2 s ⋅ C 2 = J s ⋅ A 2 = kg ⋅ m 2 s 3 ⋅ A 2 in which the following units appear: volt, siemens, second, henry, kilogram and coulomb.
In many cases the resistance of a conductor in ohms is constant within a certain range of voltages and other parameters. These are called linear resistors. In other cases resistance varies. A vowel of the prefixed units kiloohm and megaohm is omitted, producing kilohm and megohm. In alternating current circuits, electrical impedance is measured in ohms; the siemens is the SI derived unit of electric conductance and admittance known as the mho. The power dissipated by a resistor may be calculated from its resistance, the voltage or current involved; the formula is a combination of Ohm's law and Joule's law: P = V ⋅ I = V 2 R = I 2 ⋅ R where: P is the power R is the resistance V is the voltage across the resistor I is the current through the resistorA linear resistor has a constant resistance value over all applied voltages or currents. Non-linear resistors have a value. Where alternating current is applied to the circuit, the relation above is true at any instant but calculation of average power over an interval of time requires integration of "instantaneous" power over that interval.
Since the ohm belongs to a coherent system of units, when each of these quantities has its corresponding SI unit (watt for P, ohm for R, volt for V and ampere for I, which are related as in § Definition, this formula remains valid numerically when these units are used. The rapid rise of electrotechnology in the last half of the 19th century created a demand for a rational, coherent and international system of units for electrical quantities. Telegraphers and other early users of electricity in the 19th century needed a practical standard unit of measurement for resistance. Resistance was expressed as a multiple of the resistance of a standard length of telegraph wires. Electrical units so defined were not a coherent system with the units for energy, mass and time, requiring conversion factors to be used in calculations relating energy or power to resistance. Two different methods of establishing a system of electrical units can be chosen. Various artifacts, such as a length of wire or a standard electrochemical cell, could be specified as producing defined quantities for resistance, so on.
Alternatively, the electrical units can be related to the mechanical units by defining, for example, a unit of current that gives a specified force between two wires, or a unit of charge that gives a unit of force between two unit charges. This latter method ensures coherence with the units of energy. Defining a unit for resistance, coherent with units of energy and time in effect requires defining units for potential and current, it is desirable that one unit of electrical potential will force one unit of electric current through one unit of electrical resistance, doing one unit of work in one unit of time, otherwi
Coaxial cable, or coax is a type of electrical cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. Many coaxial cables have an insulating outer sheath or jacket; the term coaxial comes from the outer shield sharing a geometric axis. Coaxial cable was invented by English engineer and mathematician Oliver Heaviside, who patented the design in 1880. Coaxial cable is a type of transmission line, used to carry high frequency electrical signals with low losses, it is used in such applications as telephone trunklines, broadband internet networking cables, high speed computer data busses, carrying cable television signals, connecting radio transmitters and receivers to their antennas. It differs from other shielded cables because the dimensions of the cable and connectors are controlled to give a precise, constant conductor spacing, needed for it to function efficiently as a transmission line. Coaxial cable is used as a transmission line for radio frequency signals.
Its applications include feedlines connecting radio transmitters and receivers to their antennas, computer network connections, digital audio, distribution of cable television signals. One advantage of coaxial over other types of radio transmission line is that in an ideal coaxial cable the electromagnetic field carrying the signal exists only in the space between the inner and outer conductors; this allows coaxial cable runs to be installed next to metal objects such as gutters without the power losses that occur in other types of transmission lines. Coaxial cable provides protection of the signal from external electromagnetic interference. Coaxial cable conducts electrical signal using an inner conductor surrounded by an insulating layer and all enclosed by a shield one to four layers of woven metallic braid and metallic tape; the cable is protected by an outer insulating jacket. The shield is kept at ground potential and a signal carrying voltage is applied to the center conductor; the advantage of coaxial design is that electric and magnetic fields are restricted to the dielectric with little leakage outside the shield.
Conversely and magnetic fields outside the cable are kept from interfering with signals inside the cable. Larger diameter cables and cables with multiple shields have less leakage; this property makes coaxial cable a good choice for carrying weak signals that cannot tolerate interference from the environment or for stronger electrical signals that must not be allowed to radiate or couple into adjacent structures or circuits. Common applications of coaxial cable include video and CATV distribution, RF and microwave transmission, computer and instrumentation data connections; the characteristic impedance of the cable is determined by the dielectric constant of the inner insulator and the radii of the inner and outer conductors. In radio frequency systems, where the cable length is comparable to the wavelength of the signals transmitted, a uniform cable characteristic impedance is important to minimize loss; the source and load impedances are chosen to match the impedance of the cable to ensure maximum power transfer and minimum standing wave ratio.
Other important properties of coaxial cable include attenuation as a function of frequency, voltage handling capability, shield quality. Coaxial cable design choices affect physical size, frequency performance, power handling capabilities, flexibility and cost; the inner conductor might be stranded. To get better high-frequency performance, the inner conductor may be silver-plated. Copper-plated steel wire is used as an inner conductor for cable used in the cable TV industry; the insulator surrounding the inner conductor may be solid plastic, a foam plastic, or air with spacers supporting the inner wire. The properties of the dielectric insulator determine some of the electrical properties of the cable. A common choice is a solid polyethylene insulator, used in lower-loss cables. Solid Teflon is used as an insulator; some coaxial lines have spacers to keep the inner conductor from touching the shield. Many conventional coaxial cables use braided copper wire forming the shield; this allows the cable to be flexible, but it means there are gaps in the shield layer, the inner dimension of the shield varies because the braid cannot be flat.
Sometimes the braid is silver-plated. For better shield performance, some cables have a double-layer shield; the shield might be just two braids, but it is more common now to have a thin foil shield covered by a wire braid. Some cables may invest in more than two shield layers, such as "quad-shield", which uses four alternating layers of foil and braid. Other shield designs sacrifice flexibility for better performance; those cables cannot be bent as the shield will kink, causing losses in the cable. When a foil shield is used a small wire conductor incorporated into the foil makes soldering the shield termination easier. For high-power radio-frequency transmission up to about 1 GHz, coaxial cable with a solid copper outer conductor is available in sizes of 0.25 inch upward. The outer conductor is corrugated like a bellows to permit flexibility and the inner conductor is held in position by a plastic spiral to approximate an air dielectric. One brand name for such cable is Heliax. Coaxial cables require an internal structure of an insulating material to maintain the spacing between the center conductor and shield.
RG-59/U is a specific type of coaxial cable used for low-power video and RF signal connections. The cable has a characteristic impedance of 75 ohms, a capacitance of around 20pF/ft; the 75 ohm impedance matches a dipole antenna in free space. RG was a unit indicator for bulk radio frequency cable in the U. S. military's Joint Electronics Type Designation System. The suffix /U means for general utility use; the number 59 was assigned sequentially. The RG unit indicator is no longer part of the JETDS system and cable sold today under the RG-59 label does not meet military specifications. RG-59 is used at baseband video frequencies, such as composite video, it may be used for broadcast frequencies, but its high-frequency losses are too high to allow its use over long distances. In cases where the transmission distance is too long for these media, such options as UTP or fiber optic can be used. RG-59 coaxial cable is packed with consumer equipment, such as VCRs or digital cable/satellite receivers. Manufacturers tend to include only RG-59 cables.
However, given the short lengths provided, this is sufficient for its typical use. RG-59 is used to synchronize two digital audio devices, such as ADAT optical devices; this is called word clock. BNC connector Coaxial cable RG-58 – A similar cable but with an impedance of 50 or 52 ohms Straw, R Dean; the ARRL Handbook for Radio Communications 2006. Newington, CT: American Radio Relay League. ISBN 0-87259-949-3. OCLC 62026192. CS1 maint: Extra text: authors list
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 other personal radio service allocations such as FRS, GMRS, MURS, UHF CB and the Amateur Radio Service. In many countries, CB operation does not require a license, it may be used for business or personal communications. Like many other two-way radio services, citizens band channels are shared by many users. Only one station may transmit at a time, it is customary for stations waiting to use a shared channel to broadcast the single word "Break" followed by the channel number, during a lull in the conversation. This informs people using the channel. Multiple countries have created similar radio services, with varying technical standards and requirements for licensing. While they may be known by other names, such as the General Radio Service in Canada, they use similar frequencies and have similar uses, similar technical standards.
Although licenses may be required, eligibility is simple. Some countries have personal radio services in the UHF band, such as the European PMR446 and the Australian UHF CB; the citizens band radio service originated in the United States as one of several personal radio services regulated by the Federal Communications Commission. These services began in 1945 to permit citizens a radio band for personal communication. In 1948, the original CB radios were designed for operation on the 460–470 MHz UHF band. There were two classes of CB radio: "A" and "B". Class B radios had simpler technical requirements, were limited to a smaller frequency range. Al Gross established the Citizens Radio Corporation during the late 1940s to manufacture Class B handhelds for the general public. Ultra-high frequency radios, at the time, were neither practical nor affordable for the average consumer. On September 11, 1958 the Class D CB service was created on 27 MHz, this band became what is popularly known today as "Citizens Band".
Only 23 channels were available at the time. Some hobbyists continue to use the designation "11 meters" to refer to the Citizens Band and adjoining frequencies. Part 95 of the Code of Federal Regulations regulates the Class D CB service, on the 27 MHz band, since the 1970s and continuing today. Most of the 460–470 MHz band was reassigned for business and public-safety use. Class B CB is a more distant ancestor of the Family Radio Service; the Multi-Use Radio Service is another two-way radio service in the VHF high band. An unsuccessful petition was filed in 1973 to create a Class E CB service at 220 MHz, opposed by amateur radio organizations and others. There are several other classes of personal radio services for specialized purposes. During the 1960s, the service was popular among truck drivers and radio hobbyists. By the late 1960s advances in solid-state electronics allowed the weight and cost of the radios to fall, giving the public access to a communications medium only available to specialists.
CB clubs were formed. After the 1973 oil crisis, the U. S. government imposed a nationwide 55 mph speed limit, fuel shortages and rationing were widespread. Drivers used CB radios to locate service stations with better supplies of fuel, to notify other drivers of speed traps, to organize blockades and convoys in a 1974 strike protesting the new speed limit and other trucking regulations; the radios were crucial for independent truckers. The use of CB radios in 1970s films such as Smokey and the Bandit, Breaker! Breaker! and Convoy, popular novelty songs such as C. W. McCall's "Convoy", providing inspiration for songs like "Breaker-Breaker" from the Outlaws, on television series such as Movin' On and The Dukes of Hazzard established CB radio as a nationwide craze in the United States in the mid- to late 1970s. CB required a purchased license and the use of a callsign. Rules on authorized use of CB radio led to widespread disregard of the regulations. Betty Ford, the former First Lady of the United States, used the CB handle "First Mama".
Voice actor Mel Blanc was an active CB operator using "Bugs" or "Daffy" as his handle and talking on the air in the Los Angeles area in one of his many voice characters. He appeared in an interview in the NBC Knowledge television episode about CB radio in 1978. Similar to Internet chat rooms a quarter-century CB allowed people to get to know one another in a quasi-anonymous manner; the U. S. had 23 CB channels.
A two-way radio is a radio that can both transmit and receive a signal, unlike a broadcast receiver which only receives content. It is an audio transceiver designed for bidirectional person-to-person voice communication with other users with similar radios using the same radio frequency. Two-way radios are available in stationary base and hand-held portable configurations. Hand-held two-way radios are called walkie-talkies, handie-talkies or hand-helds. Two-way radio systems operate in a half-duplex mode: the operator can talk, or he can listen, but not at the same time. A push-to-talk or Press To Transmit button activates the transmitter. Other Full-duplex is achieved by the use of two different frequencies or by frequency-sharing methods to carry the two directions of the conversation simultaneously. Methods for mitigating the self interference caused by simultaneous transmission and reception on different but close-spaced frequencies include using two antennas, or dynamic solid-state filters.
Time-division technologies are used for mitigating self interference by simultaneous transmission and reception on the same frequency. Installation of receivers and transmitters at the same fixed location allowed exchange of messages wirelessly; as early as 1907, two-way telegraphy traffic across the Atlantic Ocean was commercially available. By 1912, commercial and military ships carried both transmitters and receivers, allowing two-way communication in close to real-time with a ship, out of sight of land; the first mobile two-way radio was developed in Australia in 1923 by Senior Constable Frederick William Downie of the Victorian Police. The Victoria Police were the first in the world to use wireless communication in cars, putting an end to the inefficient status reports via public telephone boxes, used until that time; the first sets took up the entire back seat of the Lancia patrol cars. As radio equipment became more powerful and easier to use, smaller vehicles had two-way radio communication equipment installed.
Installation of radio equipment in aircraft allowed scouts to report back observations in real-time, not requiring the pilot to drop messages to troops on the ground below or to land and make a personal report. In 1933, the Bayonne, New Jersey police department operated a two-way system between a central fixed station and radio transceivers installed in police cars. During World War II walkie-talkie hand-held radio transceivers were extensively used by air and ground troops, both by the Allies and the Axis. Early two-way schemes allowed only one station to transmit at a time while others listened, since all signals were on the same radio frequency – this was called "simplex" mode. Code and voice operations required a simple communication protocol to allow all stations to cooperate in using the single radio channel, so that one station's transmissions were not obscured by another's. By using receivers and transmitters tuned to different frequencies and solving the problems introduced by operation of a receiver next to a transmitter, simultaneous transmission and reception was possible at each end of a radio link, in so-called "full duplex" mode.
The first radio systems could not transmit voice. This required training of operators in use of Morse code. On a ship, the radio operating officers had no other duties than handling radio messages; when voice transmission became possible, dedicated operators were no longer required and two-way radio use became more common. Today's two-way mobile radio equipment is nearly as simple to use as a household telephone, from the point of view of operating personnel, thereby making two-way communications a useful tool in a wide range of personal and military roles. Two-way radio systems can be classified in several ways depending on their attributes. Conventional radios operate on fixed RF channels. In the case of radios with multiple channels, they operate on one channel at a time; the proper channel is selected by a user. The user operates a channel selector on the radio control panel to pick the appropriate channel. In multi-channel systems, channels are used for separate purposes. A channel may be reserved for a geographic area.
In a functional channel system, one channel may allow City of Springfield road repair crews to talk to the City of Springfield's road maintenance office. A second channel may allow road repair crews to communicate with state highway department crews. In a wide-area or geographic system, a taxi company may use one channel to communicate in the Boston, Massachusetts area and a second channel when taxis are in Providence, Rhode Island; this is referred to as Multisite operation. In this case, the driver or the radio must switch channels to maintain coverage when transitioning between each area. Most modern conventional digital radios and systems are capable of automatic "roaming" where the radio automatically switches channels on a dynamic basis; the radio accomplishes this based on the received signal strength of the radio repeater's recurring "beacon" signal and a "site" or "roam" list that identifies available geographic channels. Some analog conventional systems can be equipped with a feature called "vote-scan" that provides more limited roaming.
Radio "simulcast" technology can be used in adjacent areas, where each site is equipped with the same channel. Here, the transmitters must be synchronized, a centralized voter or receiver comparator device is required to select the best quality sign