San Francisco Bay
San Francisco Bay is a shallow estuary in the U. S. state of California. It is surrounded by a region known as the San Francisco Bay Area, dominated by the large cities San Francisco, Oakland. San Francisco Bay drains water from approximately 40 percent of California and it connects to the Pacific Ocean via the Golden Gate strait. However, this group of interconnected bays is often called the San Francisco Bay. The bay was designated a Ramsar Wetland of International Importance on February 2,2013, the bay covers somewhere between 400 and 1,600 square miles, depending on which sub-bays, wetlands, and so on are included in the measurement. The main part of the bay measures 3 to 12 miles wide east-to-west and it is the largest Pacific estuary in the Americas. Later and inlets were filled in, reducing the Bays size since the mid-19th century by as much as one third. Recently, large areas of wetlands have been restored, further confusing the issue of the Bays size, despite its value as a waterway and harbor, many thousands of acres of marshy wetlands at the edges of the bay were, for many years, considered wasted space.
As a result, soil excavated for building projects or dredged from channels was often dumped onto the wetlands, from the mid-19th century through the late 20th century, more than a third of the original bay was filled and often built on. The idea was, and remains, there are five large islands in San Francisco Bay. Alameda, the largest island, was created when a shipping lane was cut in 1901 and it is now predominantly a bedroom community. Angel Island was known as Ellis Island West because it served as the point for immigrants from East Asia. It is now a park accessible by ferry. Mountainous Yerba Buena Island is pierced by a tunnel linking the east and west spans of the San Francisco–Oakland Bay Bridge, attached to the north is the artificial and flat Treasure Island, site of the 1939 Golden Gate International Exposition. From the Second World War until the 1990s, both served as military bases and are now being redeveloped. Isolated in the center of the Bay is Alcatraz, the site of the federal penitentiary.
The federal prison on Alcatraz Island no longer functions, but the complex is a popular tourist site, despite its name, Mare Island in the northern part of the bay is a peninsula rather than an island. During the last ice age, the now filled by the bay was a large linear valley with small hills
The amateur radio service is established by the International Telecommunication Union through the International Telecommunication Regulations. National governments regulate technical and operational characteristics of transmissions and issue individual stations licenses with a call sign. Prospective amateur operators are tested for their understanding of key concepts in electronics, according to an estimate made in 2011 by the American Radio Relay League, two million people throughout the world are regularly 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 significantly smaller number, about 400,000, are located in IARU Region 1. The origins of amateur radio can be traced to the late 19th 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, as with radio in general, amateur radio was associated with various amateur experimenters and hobbyists.
Amateur radio enthusiasts have significantly contributed to science, industry, research by amateur operators has founded new industries, built economies, empowered nations, and saved lives in times of emergency. Ham radio can be used in the classroom to teach English, map skills, math, the term ham radio was first a pejorative that mocked amateur radio operators with a 19th-century term for being bad at something, like ham-fisted or ham actor. It had already used for bad wired telegraph operators. Subsequently, the community adopted it as a moniker, much like the Know-Nothing Party, or other groups. Other, more entertaining explanations have grown up throughout the years, 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, and computer networking.
Amateur radio operators use various modes of transmission to communicate, the two most common modes for voice transmissions are frequency modulation and 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 extension of landline telegraphy developed by Samuel Morse. Morse, using internationally agreed message encodings such as the Q code, 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 years a requirement to obtain an amateur license to transmit on frequencies below 30 MHz. Following changes in regulations in 2003, countries are no longer required to demand proficiency
X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, X.25 is a family of protocols that was popular during the 1980s with telecommunications companies and in financial transaction systems such as automated teller machines. X.25 was originally defined by the International Telegraph and Telephone Consultative Committee in a series of drafts and finalized in a publication known as The Orange Book in 1976. While X.25 has, to an extent, been replaced by less complex protocols, especially the Internet protocol. X.25 is one of the oldest packet-switched services available and it was developed before the OSI Reference Model. The protocol suite is designed as three conceptual layers, which correspond closely to the three layers of the seven-layer OSI model. It supports functionality not found in the OSI network layer, X.25 was developed in the ITU-T Study Group VII based upon a number of emerging data network projects.
Various updates and additions were worked into the standard, eventually recorded in the ITU series of books describing the telecommunication systems. These books were published every year with different-colored covers. The X.25 specification is only part of the set of X-Series specifications on public data networks. The public data network was the name given to the international collection of X.25 providers. Their combined network had large global coverage during the 1980s and into the 1990s, publicly accessible X.25 networks were set up in most countries during the 1970s and 1980s, to lower the cost of accessing various online services. Beginning in the early 1990s, in North America, use of X.25 networks started to be replaced by Frame Relay, most systems that required X.25 now use TCP/IP, however it is possible to transport X.25 over TCP/IP when necessary. X.25 networks are still in use throughout the world, a variant called AX.25 is used widely by amateur packet radio. Racal Paknet, now known as Widanet, is still in operation in many regions of the world, running on an X.25 protocol base.
Additionally X.25 is still under heavy use in the business even though a transition to modern protocols like X.400 is without option as X.25 hardware becomes increasingly rare. As recently as March 2006, the United States National Airspace Data Interchange Network has used X.25 to interconnect remote airfields with Air Route Traffic Control Centers, france was one of the last remaining countries where commercial end-user service based on X.25 operated. Known as Minitel it was based on Videotex, itself running on X.25, as planned, service was terminated 30 June 2012
Morse code is a method of transmitting text 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. It is named for Samuel F. B, Morse, an inventor of the telegraph. Because many non-English natural languages use more than the 26 Roman letters, each Morse code symbol represents either a text character or a prosign and is represented by a unique sequence of dots and dashes. The duration of a dash is three times the duration of a dot, each dot or dash is followed by a short silence, equal to the dot duration. The letters of a word are separated by an equal to three dots, and the words are separated by a space equal to seven dots. The dot duration is the unit of time measurement in code transmission. To increase the speed of the communication, the code was designed so that the length of each character in Morse varies approximately inversely to its frequency of occurrence in English. Thus the most common letter in English, the letter E, has the shortest code, Morse code is used by some amateur radio operators, although knowledge of and proficiency with it is no longer required for licensing in most countries.
Pilots and air controllers usually need only a cursory understanding. Aeronautical navigational aids, such as VORs and NDBs, constantly identify in Morse code, compared to voice, Morse code is less sensitive to poor signal conditions, yet still comprehensible to humans without a decoding device. Morse is, therefore, an alternative to synthesized speech for sending automated data to skilled listeners on voice channels. Many amateur radio repeaters, for example, identify with Morse, in an emergency, Morse code can be sent by improvised methods that can be easily keyed on and off, making it one of the simplest and most versatile methods of telecommunication. The most common signal is SOS or three dots, three dashes, and three dots, internationally recognized by treaty. Beginning in 1836, the American artist Samuel F. B, the American physicist Joseph Henry, and Alfred Vail developed an electrical telegraph system. This system sent pulses of current along wires which controlled an electromagnet that was located at the receiving end of the telegraph system.
A code was needed to transmit natural language using only these pulses, around 1837, therefore, developed an early forerunner to the modern International Morse code. Around the same time, Carl Friedrich Gauss and Wilhelm Eduard Weber as well as Carl August von Steinheil had already used codes with varying lengths for their telegraphs. In 1837, William Cooke and Charles Wheatstone in England began using a telegraph that used electromagnets in its receivers
The license privileges of amateur radio operators include the use of frequencies within this band for telecommunication, usually conducted locally within a range of about 100 miles. The Radio Regulations of the International Telecommunication Union allow amateur radio operations in the range from 144 to 148 MHz. In the US, that role in communications is furthered by the fact that most amateur-radio operators have a 2-meter handheld transceiver. Much of 2-meter FM operation uses a radio repeater, a receiver and transmitter that instantly retransmits a received signal on a separate frequency. Repeaters are normally located in locations such as a tall building or a hill top overlooking expanses of territory. On VHF frequencies such as 2-meters, antenna height greatly influences how far one can talk, typical reliable repeater range is about 25 miles. Some repeaters in unusually high locations, such as skyscrapers or mountain tops, reliable range is very dependent on the height of the repeater antenna and on the height and surroundings of the handheld or mobile unit attempting to access to the repeater.
Line of sight would be the ultimate in reliability, the typical hand held two meter FM transceiver produces about 5 watts of transmit power. Stations in a car or home provide higher power,25 to 75 watts, even without repeaters available, the 2-meter band provides reliable crosstown communications throughout smaller towns, making it ideal for emergency communications. Antennas for repeater work are almost always vertically polarized since 2-meter antennas on cars are usually vertically polarized, matching polarization allows for maximum signal coupling which equates to stronger signals in both directions. Simple radios for FM repeater operation have become plentiful and inexpensive in recent years, while the 2-meter band is best known as a local band using the FM Mode, there are many opportunities for long distance communications using other modes. The typical 2 meter station using CW or SSB modes consists of an exciter driving a power amplifier generating about 200–500 watts of RF power and this power is usually fed to a multi-element horizontally polarized, directional beam antenna knowns as a Yagi.
Stations that are located in high locations with views clear to the horizon have a big advantage over other stations at lower elevations. Such stations are able to communicate 100–300 miles consistently and it is not unusual to be heard at distances much further and these distances can be traversed on a daily basis without any noticeable help from known Signal Enhancements. However, when coupled with well known signal enhancements, astonishing distances can be bridged. To traverse these distances, directional Yagi antennas are almost essential and are generally horizontally polarized and these antennas provide huge signal gains over a dipole or simple vertical and make communication over several hundred miles reliable. Meteor scatter, sporadic E, and tropospheric ducting are the most common forms of VHF signal enhancement and are described further below. These Openings as they are known, are generally first spotted by amateurs operating SSB, completion of contacts using these weak signal modes involves the exchange of signal level reports and location by grid square which is known as the Maidenhead Locator System
Internet protocol suite
The Internet protocol suite is the conceptual model and set of communications protocols used on the Internet and similar computer networks. It is commonly known as TCP/IP because the protocols in the suite are the Transmission Control Protocol. It is occasionally known as the Department of Defense model, because the development of the model was funded by DARPA. The Internet protocol suite provides end-to-end data communication specifying how data should be packetized, transmitted and received and this functionality is organized into four abstraction layers which are used to sort all related protocols according to the scope of networking involved. Technical standards specifying the Internet protocol suite and many of its constituent protocols are maintained by the Internet Engineering Task Force, the Internet protocol suite model is a simpler model developed prior to the OSI model. The Internet protocol suite resulted from research and development conducted by the Defense Advanced Research Projects Agency in the late 1960s, after initiating the pioneering ARPANET in 1969, DARPA started work on a number of other data transmission technologies.
In 1972, Robert E. Cerf credits Hubert Zimmermann and Louis Pouzin, designer of the CYCLADES network, the protocol was implemented as the Transmission Control Program, first published in 1974. Initially, the TCP managed both datagram transmissions and routing, but as the protocol grew, other researchers recommended a division of functionality into protocol layers, postel stated, “we are screwing up in our design of Internet protocols by violating the principle of layering”. Encapsulation of different mechanisms was intended to create an environment where the layers could access only what was needed from the lower layers. A monolithic design would be inflexible and lead to scalability issues, the Transmission Control Program was split into two distinct protocols, the Transmission Control Protocol and the Internet Protocol. The new suite replaced all protocols used previously and this design is known as the end-to-end principle. Using this design, it possible to connect almost any network to the ARPANET, irrespective of the local characteristics.
One popular expression is that TCP/IP, the product of Cerf and Kahns work. A computer called a router is provided with an interface to each network and it forwards packets back and forth between them. Originally a router was called gateway, but the term was changed to avoid confusion with other types of gateways, from 1973 to 1974, Cerfs networking research group at Stanford worked out details of the idea, resulting in the first TCP specification. A significant technical influence was the early networking work at Xerox PARC, DARPA contracted with BBN Technologies, Stanford University, and the University College London to develop operational versions of the protocol on different hardware platforms. Four versions were developed, TCP v1, TCP v2, TCP v3 and IP v3, the last protocol is still in use today. In 1975, a two-network TCP/IP communications test was performed between Stanford and University College London, in November,1977, a three-network TCP/IP test was conducted between sites in the US, the UK, and Norway
Federal Communications Commission
The FCC works towards six goals in the areas of broadband, the spectrum, the media, public safety and homeland security, and modernizing itself. The FCC was formed by the Communications Act of 1934 to replace the radio regulation functions of the Federal Radio Commission, the FCC took over wire communication regulation from the Interstate Commerce Commission. The FCCs mandated jurisdiction covers the 50 states, the District of Columbia, the FCC provides varied degrees of cooperation and leadership for similar communications bodies in other countries of North America. The FCC is funded entirely by regulatory fees and it has an estimated fiscal-2016 budget of US$388 million. Consistent with the objectives of the Act as well as the 1993 Government Performance and Results Act and these are, Broadband All Americans should have affordable access to robust and reliable broadband products and services. Competition Competition in the provision of services, both domestically and overseas, supports the Nations economy.
The competitive framework for communications services should foster innovation and offer consumers reliable, Media The Nations media regulations must promote competition and diversity and facilitate the transition to digital modes of delivery. Public Safety and Homeland Security Communications during emergencies and crisis must be available for public safety, defense, the Nations critical communications infrastructure must be reliable, interoperable and rapidly restorable. The FCC is directed by five appointed by the President of the United States and confirmed by the United States Senate for five-year terms. The U. S. President designates one of the commissioners to serve as chairman, only three commissioners may be members of the same political party. None of them may have a financial interest in any FCC-related business, commissioners may continue serving until the appointment of their replacements, but may not serve beyond the end of the next session of Congress following term expiration.
In practice, as of 2016 this means that commissioners may serve up to 1 1/2 years beyond the term expiration dates listed above if no replacement is appointed. The Consumer & Governmental Affairs Bureau develops and implements the FCCs consumer policies, CGB serves as the public face of the FCC through outreach and education, as well as through their Consumer Center, which is responsible for responding to consumer inquiries and complaints. CGB maintains partnerships with state and tribal governments in such areas as emergency preparedness. The Enforcement Bureau is responsible for enforcement of provisions of the Communications Act 1934, FCC rules, FCC orders, major areas of enforcement that are handled by the Enforcement Bureau are consumer protection, local competition, public safety, and homeland security. S. The International Bureau oversees FCC compliance with the international Radio Regulations, the Media Bureau handles post-licensing matters regarding direct broadcast satellite service.
The Wireless Telecommunications Bureau regulates domestic wireless telecommunications programs and policies, the Wireline Competition Bureau develops policy concerning wire line telecommunications. The Wireline Competition Bureaus main objective is to promote growth and economical investments in technology infrastructure, markets
This is a technique in which a telecommunication signal is transmitted on a bandwidth considerably larger than the frequency content of the original information. Frequency hopping is a modulation technique used in spread spectrum signal transmission. This technique decreases the potential interference to other receivers while achieving privacy, spread spectrum generally makes use of a sequential noise-like signal structure to spread the normally narrowband information signal over a relatively wideband band of frequencies. The receiver correlates the received signals to retrieve the information signal. Frequency-hopping spread spectrum, direct-sequence spread spectrum, time-hopping spread spectrum, chirp spread spectrum, ultra-wideband is another modulation technique that accomplishes the same purpose, based on transmitting short duration pulses. Wireless standard IEEE802.11 uses either FHSS or DSSS in its radio interface, techniques known since the 1940s and used in military communication systems since the 1950s spread a radio signal over a wide frequency range several magnitudes higher than minimum requirement. DS is good at resisting continuous-time narrowband jamming, while FH is better at resisting pulse jamming, by contrast, in narrowband systems where the signal bandwidth is low, the received signal quality will be severely lowered if the jamming power happens to be concentrated on the signal bandwidth.
Multiple access capability, known as code-division multiple access or code-division multiplexing and their approach was unique in that frequency coordination was done with paper player piano rolls - a novel approach which was never put into practice. A synchronous digital system is one that is driven by a signal and. In fact, a clock signal would have all its energy concentrated at a single frequency. It has become a technique to gain regulatory approval because it requires only simple equipment modification. It is even more popular in portable electronics devices because of faster clock speeds, since these devices are designed to be lightweight and inexpensive, traditional passive, electronic measures to reduce EMI, such as capacitors or metal shielding, are not viable. Active EMI reduction techniques such as spread-spectrum clocking are needed in these cases, spread-spectrum clocking, like other kinds of dynamic frequency change, can create challenges for designers. Principal among these is clock/data misalignment, or clock skew, note that this method does not reduce total radiated energy, and therefore systems are not necessarily less likely to cause interference.
Spreading energy over a larger bandwidth effectively reduces electrical and magnetic readings within narrow bandwidths, typical measuring receivers used by EMC testing laboratories divide the electromagnetic spectrum into frequency bands approximately 120 kHz wide. If the system under test were to all its energy in a narrow bandwidth. Distributing this same energy into a larger bandwidth prevents systems from putting enough energy into any one narrowband to exceed the statutory limits, FCC certification testing is often completed with the spread-spectrum function enabled in order to reduce the measured emissions to within acceptable legal limits. However, the spread-spectrum functionality may be disabled by the user in some cases and this might be considered a loophole, but is generally overlooked as long as spread-spectrum is enabled by default
Network topology is the arrangement of the various elements of a computer network. Essentially, it is the structure of a network and may be depicted physically or logically. Distances between nodes, physical interconnections, transmission rates, or signal types may differ between two networks, yet their topologies may be identical, an example is a local area network. Conversely, mapping the data flow between the components determines the topology of the network. Two basic categories of network topologies exist, physical topologies and logical topologies, the cabling layout used to link devices is the physical topology of the network. This refers to the layout of cabling, the locations of nodes, a networks logical topology is not necessarily the same as its physical topology. For example, the twisted pair Ethernet using repeater hubs was a logical bus topology carried on a physical star topology. Token ring is a ring topology, but is wired as a physical star from the media access unit. Logical topologies are often associated with media access control methods.
Some networks are able to change their logical topology through configuration changes to their routers. The study of network topology recognizes eight basic topologies, point-to-point, star, ring or circular, tree, the simplest topology with a dedicated link between two endpoints. Easiest to understand, of the variations of point-to-point topology, is a point-to-point communications channel that appears, to the user, a childs tin can telephone is one example of a physical dedicated channel. Using circuit-switching or packet-switching technologies, a point-to-point circuit can be set up dynamically, switched point-to-point topologies are the basic model of conventional telephony. The value of a permanent point-to-point network is unimpeded communications between the two endpoints, the value of an on-demand point-to-point connection is proportional to the number of potential pairs of subscribers and has been expressed as Metcalfes Law. In local area networks where bus topology is used, each node is connected to a single cable and this central cable is the backbone of the network and is known as the bus. A signal from the travels in both directions to all machines connected on the bus cable until it finds the intended recipient.
If the machine address does not match the address for the data. Alternatively, if the matches the machine address, the data is accepted
Ultra high frequency
Ultra high frequency is the ITU designation for radio frequencies in the range between 300 MHz and 3 GHz, known as the decimetre band as the wavelengths range from one meter to one decimetre. Radio waves with frequencies above the UHF band fall into the SHF or microwave frequency range, lower frequency signals fall into the VHF or lower bands. UHF radio waves propagate mainly by line of sight, they are blocked by hills, the IEEE defines the UHF radar band as frequencies between 300 MHz and 1 GHz. Two other IEEE radar bands overlap the ITU UHF band, the L band between 1 and 2 GHz and the S band between 2 and 4 GHz. Radio waves in the UHF band travel almost entirely by propagation and ground reflection, there is very little reflection from the ionosphere. They are blocked by hills and cannot travel far beyond the horizon, atmospheric moisture reduces, or attenuates, the strength of UHF signals over long distances, and the attenuation increases with frequency. UHF TV signals are generally more degraded by moisture than lower bands, occasionally when conditions are right, UHF radio waves can travel long distances by tropospheric ducting as the atmosphere warms and cools throughout the day.
The length of an antenna is related to the length of the radio waves used, the UHF antenna is stubby and short, at UHF frequencies a quarter-wave monopole, the most common omnidirectional antenna is between 2.5 and 25 cm long for example. UHF is widely used in telephones, cell phones, walkie-talkies and other two-way radio systems from short range up to the visual horizon. Their transmissions do not travel far, allowing frequency reuse, public safety, business communications and personal radio services such as GMRS, PMR446, and UHF CB are often found on UHF frequencies as well as IEEE802.11 wireless LANs. The widely adapted GSM and UMTS cellular networks use UHF cellular frequencies, radio repeaters are used to retransmit UHF signals when a distance greater than the line of sight is required. Omnidirectional UHF antennas used on mobile devices are usually short whips, higher gain omnidirectional UHF antennas can be made of collinear arrays of dipoles and are used for mobile base stations and cellular base station antennas.
The short wavelengths allow high gain antennas to be conveniently small, high gain antennas for point-to-point communication links and UHF television reception are usually Yagi, log periodic, corner reflectors, or reflective array antennas. At the top end of the band slot antennas and parabolic dishes become practical, for television broadcasting specialized vertical radiators that are mostly modifications of the slot antenna or helical antenna are used, the slotted cylinder, zig-zag, and panel antennas. UHF television broadcasting fulfilled the demand for additional over-the-air television channels in urban areas, much of the bandwidth has been reallocated to land mobile, trunked radio and mobile telephone use. UHF channels are used for digital television. UHF spectrum is used worldwide for mobile radio systems for commercial, public safety. Many personal radio services use frequencies allocated in the UHF band, major telecommunications providers have deployed voice and data cellular networks in UHF/VHF range
SRI International is an American nonprofit research institute headquartered in Menlo Park, California. The trustees of Stanford University established SRI in 1946 as a center of innovation to support development in the region. The organization was founded as the Stanford Research Institute, SRI formally separated from Stanford University in 1970 and became known as SRI International in 1977. SRI describes its mission as creating world-changing solutions to make people safer, healthier and it performs client-sponsored research and development for government agencies, commercial businesses, and private foundations. It licenses its technologies, forms strategic partnerships, sells products, SRIs annual revenue in 2014 was approximately $540 million. SRIs headquarters are located near the Stanford University campus, jeffrey has served as SRIs president and CEO since September 2014. Sarnoff Corporation, an owned subsidiary of SRI since 1988, was fully integrated into SRI in January 2011. SRI has received more than 4,000 patents and patent applications worldwide, in the 1920s, Stanford University professor Robert E.
Swain proposed creating a research institute in the Western United States. Herbert Hoover, a trustee of Stanford University, was a proponent of an institute. The development of the institute was delayed by the Great Depression in the 1930s and World War II in the 1940s, with three separate attempts leading to its formation in 1946. In August 1945, Maurice Nelles, Morlan A. Visel, a second attempt was made by Henry T. Heald, president of the Illinois Institute of Technology. In 1945, Heald wrote a report recommending a research institute on the West Coast, a third attempt was made by Fred Terman, Stanford Universitys dean of engineering. Termans proposal followed Healds, but focused on faculty and student research more than contract research, the trustees of Stanford University voted to create the organization in 1946. It was structured so that its goals were aligned with the charter of the university—to advance scientific knowledge and to benefit the public at large, not just the students of Stanford University.
The trustees were named as the general members, and elected SRIs directors, if the organization were dissolved. Research chemist William F. Talbot became the first director of the institute and this and other issues, including frustration with Tresidders micromanagement of the new organization, caused Talbot to repeatedly offer his resignation, which Tresidder eventually accepted. Talbot was replaced by Jesse Hobson, who had led the Armour Research Foundation. SRIs first research project investigated whether the plant could be used as a source of natural rubber
Terminal node controller
A terminal node controller is a device used by amateur radio operators to participate in AX.25 packet radio networks. It is similar in function to the Packet Assembler/Disassemblers used on X.25 networks, the TNC was originally developed by Doug Lockhart, VE7APU, of Vancouver, British Columbia, and popularized by the Tucson Amateur Packet Radio association with the TNC-1 and TNC-2. A typical model consists of a microprocessor, a modem, and software that implements the AX.25 protocol, because the TNC contains all the intelligence needed to communicate over an AX.25 network, no external computer is required. All of the resources can be accessed using a dumb terminal. The TNC connects to the terminal and a radio transceiver, data from the terminal is formatted into AX.25 packets and modulated into audio signals for transmission by the radio. Received signals are demodulated, the data unformatted, and the output sent to the terminal for display, in addition to these functions, the TNC manages the radio channel according to guidelines in the AX.25 specification.
TNCs were uniquely necessary when home computers lacked the sophistication needed to manage a network connection. They are still used throughout a very popular position reporting network known as Automatic Packet Reporting System on 144.390 MHz. Powerful desktop computers are commonplace in amateur radio stations, software modems using the computers soundcard have lowered hardware requirements even further. However, with their lower cost comes additional tweaking in order to make them work properly, some handheld and mobile VHF radios currently on the market incorporate TNC abilities within the radio itself in support of the APRS protocol. Many TNCs are still in use, especially in unattended stations where reliability is important, the importance of location to the APRS system has fueled development of a new generation of small low-power TNCs often integrated with a GPS module for use in mobile tracking stations. APRS digipeating protocols require specific naming conventions, and older TNCs may not have the support to be used as a digipeater.
However, almost any TNC can be pressed into service for Home or Tracker use, TNCs that were clones of the popular TAPR TNC-2 may be upgradeable via the UIDIGI firmware project. Although typically described as data ports, the interface between a radio and a TNC is almost entirely analog audio, the connectors used for this purpose varies widely across TNC manufacturers, but modern radios that offer data ports have widely adopted the Mini-DIN 6-pin connector. Also used are full-size DIN connectors, modular connectors, and combinations of mini-. 6-pin Mini-DIN The interface between a radio and a terminal is typically a standard serial port — a DB-25 or DE-9 connector carrying asynchronous start-stop bytes with RS-232 signal levels, TNCs were originally designed to accept messages from a human typing on a dumb terminal. However, typically a human uses a more sophisticated software package running on a computer that sends messages to the TNC using the KISS protocol or the 6PACK protocol