1.
Avalanche transceiver
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Avalanche transceivers or avalanche beacon are a class of active radio beacon transceivers operating at 457 kHz and specialized for the purpose of finding people or equipment buried under snow. When the owner sets out on a descent, the transceiver is activated. A457 kHz beacon is a device that requires batteries. A ski suit may contain a passive RECCO transponder sewn into the clothing. Early avalanche beacons transmitted at 2.275 kHz, in 1986, the international frequency standard of 457 kHz was adopted, and this remains the standard today. Many companies manufacture beacons that comply with this standard, an avalanche beacon is not considered a preventive measure against possible avalanche burial, but rather it is a way to reduce the amount of time buried. This unit, functioning at 2.275 kHz, converted the frequency to a simple tone audible to the human ear. By following the tone to where it was loudest, the operator could use it to locate the buried beacon by using a grid searching technique. In 1986, IKAR adopted the frequency of 457 kHz, in 1996 ASTM adopted the 457 kHz standard. The following are the accepted international standards for Avalanche Transceivers operating on the 457 kHz frequency. In 1997, the first digital beacon was introduced at the Winter Outdoor Retailer show by Backcountry Access under the brand name Tracker, the Tracker DTS soon became the most widely used beacon in North America, and is still sold and used by many backcountry enthusiasts. Today, consumers have a range of choices for digital beacons from companies like Ortovox, Arva, Pieps, Mammut. There are two types of beacons, digital and analog. They both adhere to the standard as described above, and only differ in the method used to indicate to the user where the buried beacon is located. Most beacons currently being sold are digital, because of their ease of use. The original avalanche beacon was a beacon which transmitted the pulsed signal as an audible tone to the user. The tone gets louder when the user is closer to the transmitting beacon and these beacons have also been augmented with LEDs that provide a visual indication of signal strength, and earpieces to increase the ability of the listener to hear the tone. Digital transceivers take the strength of the signal and the emitted dipole flux pattern and compute distance, in order to calculate the emitted dipole flux pattern, a digital transceiver must have at least two antennas, although most modern transceivers have three
2.
Transmitter
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In electronics and telecommunications a transmitter or radio transmitter is an electronic device which generates a radio frequency alternating current. When a connected antenna is excited by this current, the antenna emits radio waves. The term transmitter is usually limited to equipment that generates radio waves for communication purposes, or radiolocation, such as radar and navigational transmitters. Generators of radio waves for heating or industrial purposes, such as ovens or diathermy equipment, are not usually called transmitters even though they often have similar circuits. The term is used more specifically to refer to a broadcast transmitter. This usage typically includes both the proper, the antenna, and often the building it is housed in. A transmitter can be a piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and a receiver combined in one unit is called a transceiver, the term transmitter is often abbreviated XMTR or TX in technical documents. The purpose of most transmitters is radio communication of information over a distance, the transmitter combines the information signal to be carried with the radio frequency signal which generates the radio waves, which is called the carrier signal. The information can be added to the carrier in several different ways, in an amplitude modulation transmitter, the information is added to the radio signal by varying its amplitude. In a frequency modulation transmitter, it is added by varying the signals frequency slightly. Many other types of modulation are used, the radio signal from the transmitter is applied to the antenna, which radiates the energy as radio waves. The antenna may be enclosed inside the case or attached to the outside of the transmitter, as in portable devices such as phones, walkie-talkies. In more powerful transmitters, the antenna may be located on top of a building or on a tower, and connected to the transmitter by a feed line. The first primitive radio transmitters were built by German physicist Heinrich Hertz in 1887 during his investigations of radio waves. These generated radio waves by a high voltage spark between two conductors, beginning in 1895 Guglielmo Marconi developed the first practical radio communication systems using spark transmitters. These spark-gap transmitters were used during the first three decades of radio, called the wireless telegraphy or spark era, vacuum tube transmitters took over because they were inexpensive and produced continuous waves, which could be modulated to transmit audio using amplitude modulation. This made possible commercial AM radio broadcasting, which began in about 1920, experimental television transmission had been conducted by radio stations since the late 1920s, but practical television broadcasting didnt begin until the 1940s
3.
Radio receiver
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In radio communications, a radio receiver is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna, the antenna intercepts radio waves and converts them to tiny alternating currents which are applied to the receiver, and the receiver extracts the desired information. The information produced by the receiver may be in the form of sound, a radio receiver may be a separate piece of electronic equipment, or an electronic circuit within another device. The most familiar form of radio receiver is a broadcast receiver, often just called a radio, the sound is produced either by a loudspeaker in the radio or an earphone which plugs into a jack on the radio. The radio requires electric power, provided either by batteries inside the radio or a cord which plugs into an electric outlet. All radios have a control to adjust the loudness of the audio. The frequency of radio stations is usually listed prominently in their advertising, in order to select a particular station to receive, the radio is adjusted to the frequency of the desired transmitter. In some radios this is done by the user turning a tuning knob until the station is heard in the radios loudspeaker. In most countries radio broadcasting is permitted using two different methods of modulation, that is, methods of adding the signal to the radio wave, AM and FM. In amplitude modulation the strength of the signal is varied by the audio signal. AM broadcasting is permitted on AM broadcast bands between 148 and 283 kHz in the low range and 526 and 1706 kHz in the medium frequency range of the radio spectrum. In frequency modulation the frequency of the signal is varied slightly by the audio signal. FM broadcasting is permitted in the FM broadcast bands between about 65 and 108 MHz in the high frequency range. The exact frequency ranges vary somewhat in different countries, radios sold in each receive the correct frequency range for that country. Most broadcast radios, called AM/FM radios, can receive both AM and FM bands, and have a switch to select which band to receive. Limited AM broadcasting is permitted in parts of the high frequency band called the shortwave band. Shortwave listening requires a receiver that can receive these bands, called a shortwave receiver, at these frequencies, radio waves transmitted into the sky can reflect from a layer in the atmosphere called the ionosphere, returning to earth at transcontinental distances. So shortwaves are used for long distance international broadcasting, often by governmental public service broadcasting organizations like the BBC, due to their lower frequency, AM radio stations can often be received at longer distances than FM stations, at hundreds of miles
4.
Transponder
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In telecommunication, a transponder is one of two types of devices. The term is a portmanteau for transmitter-responder and it is variously abbreviated as XPDR, XPNDR, TPDR or TP. A communications satellite’s channels are called transponders, because each is a separate transceiver or repeater, with digital video data compression and multiplexing, several video and audio channels may travel through a single transponder on a single wideband carrier. Original analog video only has one channel per transponder, with subcarriers for audio, non-multiplexed radio stations can also travel in single channel per carrier mode, with multiple carriers per transponder. This allows each station to transmit directly to the satellite, rather than paying for a whole transponder, in optical fiber communications, a transponder is the element that sends and receives the optical signal from a fiber. A transponder is typically characterized by its rate and the maximum distance the signal can travel. The difference between the two is that transceivers interface electrically with the host system using an interface, whereas transponders use a parallel interface to do so. In this view, transponders provide easier-to-handle lower-rate parallel signals, but are bulkier, as such, transponders can be considered as two transceivers placed back-to-back. This view also seems to be held by e. g. Fujitsu, as a result, difference in transponder functionality also might influence the functional description of related optical modules like transceivers and muxponders. Primary radar works best with large aircraft, but not so well on small. Its range is limited by terrain and rain or snow and also detects unwanted objects such as automobiles, hills. Furthermore, it cannot always estimate the altitude of an aircraft, secondary radar overcomes these limitations but it depends on a transponder in the aircraft to respond to interrogations from the ground station to make the plane more visible. Another mode called Mode S is designed to help avoiding over-interrogation of the transponder, Mode S transponders are backward compatible with Modes A and C. Mode S is mandatory in controlled airspace in many countries. Some countries have required, or are moving towards requiring. In addition, navigational aids often have transponders called RACON designed to make them out on a ships radar screen. Many modern automobiles have keys with transponders hidden inside the head of the key. The user of the car may not even be aware that the transponder is there, when a key is inserted into the ignition lock cylinder and turned, the cars computer sends a radio signal to the transponder. Unless the transponder replies with a code, the computer will not allow the engine to be started
5.
Transverter
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In radio engineering, a transverter is a radio frequency device that consists of an upconverter and a downconverter in one unit. Transverters are used in conjunction with transceivers to change the range of frequencies over which the transceiver can communicate, in electrical power engineering, a transverter is a universal electrical power converter that can combine, convert, analyze and control any combinations of DC or AC power. Transverters are used in radio to convert radio transceivers designed for use on the HF or VHF bands to operate on even higher frequency bands. A transceiver used in fashion is referred to as an IF radio. Some transverter units include transmit/receive switching built into the design, whereas other units require external switching, the use of external switching is popular in applications where preamps and amplifiers are included. Transverters can also be used in applications where the frequency is lower than the transceiver frequency. Several low frequency bands are available around the world to amateur operators, licensed experimental stations. Transverters for these LF bands generally use HF transceivers as the IF radio, some are used for communications where one or more of the stations are underground. Transverters are used to convert and combine different types of power such as solar panels, batteries, wind generators, fuel cells. By automatically analyzing and converting the power between different voltages and AC or DC, it allows for energy to flow between all types of devices. With the advent of the Smart Grid it is becoming very popular since it combines renewable energy, demand management, transverters also correct for power factor locally, which creates significant reductions in transmission loss for the grid
6.
Repeater
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In telecommunications, a repeater is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover distances or be received on the other side of an obstruction. Some types of repeaters broadcast a signal, but alter its method of transmission, for example. A broadcast relay station is a used in broadcast radio. When an information-bearing signal passes through a channel, it is progressively degraded due to loss of power. The longer the wire is, the power is lost. So with a long enough wire the call will not be audible at the other end, similarly, the farther from a radio station a receiver is, the weaker the radio signal, and the poorer the reception. A repeater is a device in a communication channel that increases the power of a signal and retransmits it. Since it amplifies the signal, it requires a source of electric power, the term repeater originated with telegraphy in the 19th century, and referred to an electromechanical device used to regenerate telegraph signals. Use of the term has continued in telephony and data communications and this is used to increase the range of telephone signals in a telephone line. They are most frequently used in trunklines that carry long distance calls, since the telephone is a duplex communication system, the wire pair carries two audio signals, one going in each direction. So telephone repeaters have to be bilateral, amplifying the signal in both directions without causing feedback, which complicates their design considerably, telephone repeaters were the first type of repeater and were some of the first applications of amplification. The development of telephone repeaters between 1900 and 1915 made long distance phone service possible, however most telecommunications cables are now fiber optic cables which use optical repeaters. Submarine cable repeater This is a type of telephone used in underwater submarine telecommunications cables. This is used to increase the range of signals in a fiber optic cable, digital information travels through a fiber optic cable in the form of short pulses of light. The light is made up of particles called photons, which can be absorbed or scattered in the fiber, however, optical amplifiers are being developed for repeaters to amplify the light itself without the need of converting it to an electric signal first. Some repeaters have been powered by light energy transmitted down the fiber with the signal and this is used to extend the range of coverage of a radio signal. A radio repeater usually consists of a receiver connected to a radio transmitter
7.
Two-way radio
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A two-way radio is a radio that can do both transmit and receive a signal, unlike a broadcast receiver which only receives content. A two-way radio allows the operator to have a conversation with other similar radios operating on the radio frequency. Two-way radios are available in mobile, stationary base and hand-held portable configurations, hand-held radios are often called walkie-talkies, handie-talkies, or just hand-helds. Two-way radio systems operate in a half-duplex mode, that is, the operator can talk, or he can listen. A push-to-talk or Press To Transmit button activates the transmitter, when it is released the receiver is active, a mobile phone or cellular telephone is an example of a two-way radio that can transmit and receive at the same time, i. e. in full-duplex mode. Full-duplex is generally 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 same-frequency transmission and reception include using two antennas, or dynamic solid-state filters. Installation of receivers and transmitters at the 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 that was out of sight of land. The first truly 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 communication in cars. The first sets took up the back seat of the Lancia patrol cars. As radio equipment became more powerful, compact, and easier to use, 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, 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 typically had no other duties than handling radio messages. When voice transmission possible, dedicated operators were no longer required. 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 control panel to pick the appropriate channel
8.
High frequency
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High frequency is the ITU designation for the range of radio frequency electromagnetic waves between 3 and 30 MHz. It is also known as the band or decameter wave as its wavelengths range from one to ten decameters. Frequencies immediately below HF are denoted medium frequency, while the band of higher frequencies is known as the very high frequency band. The HF band is a part of the shortwave band of frequencies. The band is used by shortwave broadcasting stations, aviation communication, government time stations, weather stations, amateur radio and citizens band services. By this method HF radio waves can travel beyond the horizon, around the curve of the Earth and it depends on the angle of incidence of the waves, it is lowest when the waves are directed straight upwards, and is higher with less acute angles. This means that at longer distances, where the waves graze the ionosphere at a blunt angle. The lowest usable frequency depends on the absorption in the layer of the ionosphere. This absorption is stronger at low frequencies and is stronger with increased solar activity. When all factors are at their optimum, worldwide communication is possible on HF, at many other times it is possible to make contact across and between continents or oceans. At worst, when a band is dead, no communication beyond the limited groundwave paths is possible no matter what powers, on such an open band, interference originating over a wide area affects many potential users. These issues are significant to military, safety and amateur radio users of the HF bands, other standards development such as STANAG5066 provides for error free data communications through the use of ARQ protocols. Noise, especially man-made interference from devices, tends to have a great effect on the HF bands. In recent years, concerns have risen among certain users of the HF spectrum over broadband over power lines Internet access and this is due to the frequencies on which BPL operates and the tendency for the BPL signal to leak from power lines. Some BPL providers have installed notch filters to block out certain portions of the spectrum, other electronic devices including plasma televisions can also have a detrimental effect on the HF spectrum. In aviation, HF communication systems are required for all trans-oceanic flights and these systems incorporate frequencies down to 2 MHz to include the 2182 kHz international distress and calling channel. The upper section of HF shares many characteristics with the part of VHF. The parts of this section not allocated to radio are used for local communications
9.
Spectrum analyzer
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A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals, optical spectrum analyzers also exist, which use direct optical techniques such as a monochromator to make measurements. These parameters are useful in the characterization of electronic devices, such as wireless transmitters, the display of a spectrum analyzer has frequency on the horizontal axis and the amplitude displayed on the vertical axis. To the casual observer, a spectrum analyzer looks like an oscilloscope and, in fact, the first spectrum analyzers, in the 1960s, were swept-tuned instruments. Following the discovery of the fast Fourier transform in 1965, the first FFT-based analyzers were introduced in 1967, today, there are three basic types of analyzer, the swept-tuned spectrum analyzer, the vector signal analyzer, and the real-time spectrum analyzer. Spectrum analyzer types are distinguished by the used to obtain the spectrum of a signal. By sweeping the receivers center-frequency through a range of frequencies, the output is also a function of frequency, but while the sweep centers on any particular frequency, it may be missing short-duration events at other frequencies. An FFT analyzer computes a time-sequence of periodograms, FFT refers to a particular mathematical algorithm used in the process. This is commonly used in conjunction with a receiver and analog-to-digital converter, as above, the receiver reduces the center-frequency of a portion of the input signal spectrum, but the portion is not swept. The purpose of the receiver is to reduce the rate that the analyzer must contend with. With a sufficiently low sample-rate, FFT analyzers can process all the samples, Spectrum analyzers tend to fall into four form factors, benchtop, portable, handheld and networked. This form factor is useful for applications where the spectrum analyzer can be plugged into AC power, bench top spectrum analyzers have historically offered better performance and specifications than the portable or handheld form factor. Bench top spectrum analyzers normally have multiple fans to dissipate heat produced by the processor, due to their architecture, bench top spectrum analyzers typically weigh more than 30 pounds. Some bench top spectrum analyzers offer optional battery packs, allowing them to be used away from AC power and this type of analyzer is often referred to as a portable spectrum analyzer. This form factor is useful for any applications where the spectrum analyzer needs to be taken outside to make measurements or simply carried while in use, attributes that contribute to a useful portable spectrum analyzer include, Optional battery-powered operation to allow the user to move freely outside. Clearly viewable display to allow the screen to be read in bright sunlight and this form factor is useful for any application where the spectrum analyzer needs to be very light and small. Handheld analyzers usually offer a limited capability relative to larger systems, attributes that contribute to a useful handheld spectrum analyzer include, Very low power consumption. Battery-powered operation while in the field to allow the user to move freely outside and this form factor does not include a display and these devices are designed to enable a new class of geographically-distributed spectrum monitoring and analysis applications
10.
Digital signal processing
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Digital signal processing is the use of digital processing, such as by computers, to perform a wide variety of signal processing operations. The signals processed in this manner are a sequence of numbers that represent samples of a variable in a domain such as time, space. Digital signal processing and analog signal processing are subfields of signal processing, digital signal processing can involve linear or nonlinear operations. Nonlinear signal processing is closely related to system identification and can be implemented in the time, frequency. DSP is applicable to both streaming data and static data, the increasing use of computers has resulted in the increased use of, and need for, digital signal processing. To digitally analyze and manipulate an analog signal, it must be digitized with an analog-to-digital converter, sampling is usually carried out in two stages, discretization and quantization. Discretization means that the signal is divided into equal intervals of time, quantization means each amplitude measurement is approximated by a value from a finite set. Rounding real numbers to integers is an example, the Nyquist–Shannon sampling theorem states that a signal can be exactly reconstructed from its samples if the sampling frequency is greater than twice the highest frequency of the signal. In practice, the frequency is often significantly higher than twice that required by the signals limited bandwidth. Theoretical DSP analyses and derivations are typically performed on discrete-time signal models with no amplitude inaccuracies, numerical methods require a quantized signal, such as those produced by an analog-to-digital converter. The processed result might be a frequency spectrum or a set of statistics, but often it is another quantized signal that is converted back to analog form by a digital-to-analog converter. In DSP, engineers usually study digital signals in one of the domains, time domain, spatial domain, frequency domain. They choose the domain in which to process a signal by making an assumption as to which domain best represents the essential characteristics of the signal. The most common processing approach in the time or space domain is enhancement of the signal through a method called filtering. Digital filtering generally consists of linear transformation of a number of surrounding samples around the current sample of the input or output signal. There are various ways to characterize filters, for example, A linear filter is a transformation of input samples. A causal filter uses only samples of the input or output signals. A non-causal filter can usually be changed into a filter by adding a delay to it
This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).
This article incorporates 