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In telecommunications, squelch is a circuit function that acts to suppress the audio output of a receiver in the absence of a strong input signal. Essentially, squelch is a specialized type of noise gate designed to suppress weak signals. Squelch is used in two-way radios and VHF/UHF radio scanners to eliminate the sound of noise when the radio is not receiving a desired transmission.
In telecommunications, Continuous Tone-Coded Squelch System or CTCSS is one type of in-band signaling that is used to reduce the annoyance of listening to other users on a shared two-way radio communication channel. It is sometimes referred to as tone squelch. It does this by adding a low frequency audio tone to the voice. Where more than one group of users is on the same radio frequency, CTCSS circuitry mutes those users who are using a different CTCSS tone or no CTCSS. It is sometimes referred to as a sub-channel, but this is a misnomer because no additional channels are created. All users with different CTCSS tones on the same channel are still transmitting on the identical radio frequency, and their transmissions interfere with each other; however; the interference is masked under most conditions. The CTCSS feature also does not offer any security.
The Family Radio Service (FRS) is an improved walkie-talkie radio system authorized in the United States since 1996. This personal radio service uses channelized frequencies around 462 and 467 MHz in the ultra high frequency (UHF) band. It does not suffer the interference effects found on citizens' band (CB) at 27 MHz, or the 49 MHz band also used by cordless telephones, toys, and baby monitors. FRS uses frequency modulation (FM) instead of amplitude modulation (AM). Since the UHF band has different radio propagation characteristics, short-range use of FRS may be more predictable than the more powerful license-free radios operating in the HF CB band.
A walkie-talkie, more formally known as a handheld transceiver (HT), is a hand-held, portable, two-way radio transceiver. Its development during the Second World War has been variously credited to Donald Hings, radio engineer Alfred J. Gross, Henryk Magnuski and engineering teams at Motorola. First used for infantry, similar designs were created for field artillery and tank units, and after the war, walkie-talkies spread to public safety and eventually commercial and jobsite work.
Amateur television (ATV) is the transmission of broadcast quality video and audio over the wide range of frequencies of radio waves allocated for radio amateur (Ham) use. ATV is used for non-commercial experimentation, pleasure, and public service events. Ham TV stations were on the air in many cities before commercial television stations came on the air. Various transmission standards are used, these include the broadcast transmission standards of NTSC in North America and Japan, and PAL or SECAM elsewhere, utilizing the full refresh rates of those standards. ATV includes the study of building of such transmitters and receivers, and the study of radio propagation of signals travelling between transmitting and receiving stations.
Professional mobile radio are person-to-person two-way radio voice communications systems which use portable, mobile, base station, and dispatch console radios. PMR radio systems are based on such standards as MPT-1327, TETRA, APCO 25, and DMR which are designed for dedicated use by specific organizations, or standards such as NXDN intended for general commercial use. These systems are used by police, fire, ambulance, and emergency services, and by commercial firms such as taxis and delivery services. Most systems are half-duplex, in which multiple radios share a common radio channel, and only one can transmit at a time. Transceivers are normally in receive mode, the user presses a push-to-talk button on his microphone when he wants to talk, which turns on his transmitter and turns off his receiver. They use channels in the VHF and UHF bands, giving them a limited range, usually 3 to 20 miles depending on terrain. Output power is typically limited to 4 watts. Repeaters installed on tall buildings, hills or mountain peaks are used to increase the range of systems.
PMR446 is a licence-exempt service in the UHF radio frequency band and is available for business and personal use in most countries throughout the European Union.
The 33-centimeter or 900 MHz band is a portion of the UHF radio spectrum internationally allocated to amateur radio on a secondary basis. It ranges from 902 to 928 MHz and is unique to ITU Region 2. It is primarily used for very local communications as opposed to bands lower in frequency. However, very high antennas with high gain have shown 33 centimeters can provide good long-range communications almost equal to systems on lower frequencies such as the 70 centimeter band. The band is also used by industrial, scientific, and medical (ISM) equipment, as well as low-powered unlicensed devices. Amateur stations must accept harmful interference caused by ISM users but may receive protection from unlicensed devices.
UHF CB is a class-licensed citizen's band radio service authorised by the governments of Australia, New Zealand, Vanuatu, and Malaysia in the UHF 477 MHz band. UHF CB provides 77 channels, including 32 channels allocated to repeater stations. It is similar in concept to the General Mobile Radio Service in the United States.
An amateur radio repeater is an electronic device that receives a weak or low-level amateur radio signal and retransmits it at a higher level or higher power, so that the signal can cover longer distances without degradation. Many repeaters are located on hilltops or on tall buildings as the higher location increases their coverage area, sometimes referred to as the radio horizon, or "footprint". Amateur radio repeaters are similar in concept to those used by public safety entities, businesses, government, military, and more. Amateur radio repeaters may even use commercially packaged repeater systems that have been adjusted to operate within amateur radio frequency bands, but more often amateur repeaters are assembled from receivers, transmitters, controllers, power supplies, antennas, and other components, from various sources.
A radio repeater is a combination of a radio receiver and a radio transmitter that receives a signal and retransmits it, so that two-way radio signals can cover longer distances. A repeater sited at a high elevation can allow two mobile stations, otherwise out of line-of-sight propagation range of each other, to communicate. Repeaters are found in professional, commercial, and government mobile radio systems and also in amateur radio.
In a conventional, analog two-way radio system, a standard radio has noise squelch or carrier squelch, which allows a radio to receive all transmissions. Selective calling is used to address a subset of all two-way radios on a single radio frequency channel. Where more than one user is on the same channel, selective calling can address a subset of all receivers or can direct a call to a single radio. Selective calling features fit into two major categories—individual calling and group calling. Individual calls generally have longer time-constants: it takes more air-time to call an individual radio unit than to call a large group of radios.
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The Yaesu FT-ONE is an all-mode solid state general coverage HF amateur radio (HAM) transceiver. The use of FM required an optional FM board to be installed. The unit was designed for fixed, portable or mobile operation, although the size and weight (17 kg) made it more suitable for fixed use. The FT-ONE was built by the Japanese Yaesu-Musen Corporation from 1982 to 1986. At its release, the FT-ONE was launched as the successor to the FT-902 and as the new Yaesu top-of-the-line transceiver. The FT-ONE was not only Yaesu's first fully synthesized, computer-controlled amateur band transceiver but it was also the first transceiver with a general coverage receiver. The FT-ONE was sold in the U.S., Asian and European markets. It was released in 1982 with a list price of $2800.00 US.
The Yaesu FT-817 is one of the smallest MF/HF/VHF/UHF multimode general-coverage amateur radio transceivers. The set is built by the Japanese Vertex Standard Corporation and is sold under the Yaesu brand. With internal battery pack, on board keyer, its all mode/all band capability and flexible antenna, the set is particularly well suited for portable use. The FT-817 is based on a similar circuit architecture as Yaesu's FT-857 and FT-897, so it is a compromise transceiver and incorporates its features to its low price.
The Yaesu FT-77 is a transceiver to be used in the 3,5 – 29,9 MHz shortwave radio amateur segment. This means the coverage of the 80-40-30-20-15-17-12 and 10 meter HF bands.
The Yaesu VX series is a line of two sequences of compact amateur radio handheld transceivers produced by Yaesu. There is a line of ultra-compact lower-power dual-band transceivers that started with the VX-1R and was later updated with the VX-2R and VX-3R. There is also a line of 5W tri-band transceivers that started with the VX-5R and was later updated with the VX-6R, VX-7R and VX-8R.
A personal radio service is any system that allows individual to operate radio transmitters and receivers for personal purposes with minimal or no special license or individual authorization. Personal radio services exist around the world and typically use light-weight walkie talkie portable radios. The power output, antenna size, and technical characteristics of the equipment are set by regulations in each country. Many regions have standardized personal radio service rules to allow travelers from one country to use their equipment in another country. Examples of standardized services include PMR446 and FM Citizens Band Radio (CB) in the EU and several other countries/regions. 26–27
LituanicaSAT-1 was one of the first two Lithuanian satellites. It was launched along with the second Cygnus spacecraft and 28 Flock-1 CubeSats aboard an Antares 120 carrier rocket flying from Pad 0B at the Mid-Atlantic Regional Spaceport on Wallops Island to the International Space Station. The launch was scheduled to occur in December 2013, but later was rescheduled to 9 January 2014 and occurred then. The satellite was broadcasting greetings of Lithuanian president, Mrs. Dalia Grybauskaitė. The satellite was deployed from the International Space Station via the NanoRacks CubeSat Deployer on February 28, 2014. All LituanicaSAT-1 subsystems have been turned on, tested and proved to be working properly. The mission is considered a complete success by its team of engineers. The mission ended upon the reentry and disintegration of the satellite on July 28, 2014.
