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63-454: Prior to the introduction of datalink in aviation, all communication between the aircraft and ground personnel was performed by the flight crew using voice communication, using either VHF or HF voice radios. In many cases, the voice-relayed information involved dedicated radio operators and digital messages sent to an airline teletype system or successor systems. Further, the hourly rates for flight and cabin crew salaries depended on whether

126-530: A router , which routes messages through the air-ground subnetwork. Ground equipment is made up of a network of radio transceivers managed by a central site computer called AFEPS (Arinc Front End Processor System), which handles and routes messages. Generally, ground ACARS units are either government agencies such as the Federal Aviation Administration , an airline operations headquarters, or, for small airlines or general aviation,

189-422: A VHF ground station network exists in the current area of the aircraft. VHF communication is line-of-sight propagation and the typical range is up to 200 nautical miles at high altitudes. Where VHF is absent, an HF network or satellite communication may be used if available. Satellite coverage may be limited at high latitudes (trans-polar flights). In the wake of the crash of Air France Flight 447 in 2009, there

252-447: A certain distance, and where the metal gate is replaced by an ion -sensitive membrane , electrolyte solution and reference electrode . The ISFET is widely used in biomedical applications, such as the detection of DNA hybridization , biomarker detection from blood , antibody detection, glucose measurement, pH sensing, and genetic technology . By the mid-1980s, numerous other MOSFET sensors had been developed, including

315-471: A digital signal, using an analog-to-digital converter . Since sensors cannot replicate an ideal transfer function , several types of deviations can occur which limit sensor accuracy : All these deviations can be classified as systematic errors or random errors . Systematic errors can sometimes be compensated for by means of some kind of calibration strategy. Noise is a random error that can be reduced by signal processing , such as filtering, usually at

378-502: A process to move these stations to UHF bands to free up valuable VHF spectrum for its original purpose of FM radio. In addition, by 1985 the federal government decided new TV stations are to be broadcast on the UHF band. Two new VHF channels, 9A and 12, have since been made available and are being used primarily for digital services (e.g. ABC in capital cities) but also for some new analogue services in regional areas. Because channel 9A

441-669: A proposed transmitter station. VHF is the first band at which wavelengths are small enough that efficient transmitting antennas are short enough to mount on vehicles and handheld devices, a quarter wave whip antenna at VHF frequencies is 25 cm to 2.5 meter (10 inches to 8 feet) long. So the VHF and UHF wavelengths are used for two-way radios in vehicles, aircraft, and handheld transceivers and walkie-talkies . Portable radios usually use whips or rubber ducky antennas , while base stations usually use larger fiberglass whips or collinear arrays of vertical dipoles. For directional antennas,

504-447: A request for weather information or clearances or the status of connecting flights. The response from the ground station is received on the aircraft via ACARS as well. Each airline customizes ACARS to this role to suit its needs. ACARS messages may be sent using a choice of communication methods, such as VHF or HF, either direct to ground or via satellite, using minimum-shift keying (MSK) modulation. ACARS can send messages over VHF if

567-515: A result, FM radio receivers such as those found in automobiles which are designed to tune into this frequency range could receive the audio for analog-mode programming on the local TV channel 6 while in North America. The practice largely ended with the DTV transition in 2009, although some still exist. The FM broadcast channel at 87.9 MHz is normally off-limits for FM audio broadcasting; it

630-581: A second ACARS system called Classic Aero was active as long as the plane was powered up, and kept trying to establish a connection to an Inmarsat satellite every hour. The ACARS unit on the Airbus A320 of EgyptAir Flight 804 sent ACARS messages indicating the presence of smoke in toilets and the avionics bay prior to the aircraft's crash into the Mediterranean Sea on May 19, 2016, which killed all 66 persons on board. On 24 February 2021,

693-504: A separate service provider. Messages from aircraft, especially automatically generated ones, can be pre-configured according to message type so that they are automatically delivered to the appropriate recipient just as ground-originated messages can be configured to reach the correct aircraft. The ACARS equipment on the aircraft is linked to that on the ground by the DSP. Because the ACARS network

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756-480: A sharp distinction between a biosensor and a standard chemical sensor is superfluous. Typical biomimetic materials used in sensor development are molecularly imprinted polymers and aptamers . In biomedicine and biotechnology , sensors which detect analytes thanks to a biological component, such as cells, protein, nucleic acid or biomimetic polymers , are called biosensors . Whereas a non-biological sensor, even organic (carbon chemistry), for biological analytes

819-420: A thermometer moves 1  cm when the temperature changes by 1 °C, its sensitivity is 1 cm/°C (it is basically the slope dy/dx assuming a linear characteristic). Some sensors can also affect what they measure; for instance, a room temperature thermometer inserted into a hot cup of liquid cools the liquid while the liquid heats the thermometer. Sensors are usually designed to have a small effect on what

882-418: A third-party subscription service. Usually government agencies are responsible for clearances , while airline operations handle gate assignments, maintenance, and passenger needs. Ground system provision is the responsibility of either a participating air navigation service provider (ANSP) or an aircraft operator. Aircraft operators often contract out the function to either datalink service provider (DSP) or to

945-451: Is a device that produces an output signal for the purpose of detecting a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends the information to other electronics, frequently a computer processor. Sensors are used in everyday objects such as touch-sensitive elevator buttons ( tactile sensor ) and lamps which dim or brighten by touching

1008-528: Is a radio band which, in most of the world, is used for FM broadcasting . In North America , however, this bandwidth is allocated to VHF television channel 6 (82–88 MHz). The analog audio for TV channel 6 is broadcast at 87.75 MHz (adjustable down to 87.74). Several stations, known as Frankenstations , most notably those joining the Pulse 87 franchise, have operated on this frequency as radio stations, though they use television licenses. As

1071-438: Is a self-contained analytical device that can provide information about the chemical composition of its environment, that is, a liquid or a gas phase . The information is provided in the form of a measurable physical signal that is correlated with the concentration of a certain chemical species (termed as analyte ). Two main steps are involved in the functioning of a chemical sensor, namely, recognition and transduction . In

1134-403: Is a wide range of other sensors that measure chemical and physical properties of materials, including optical sensors for refractive index measurement, vibrational sensors for fluid viscosity measurement, and electro-chemical sensors for monitoring pH of fluids. A sensor's sensitivity indicates how much its output changes when the input quantity it measures changes. For instance, if the mercury in

1197-1036: Is available in the FM broadcast band for purposes such as micro-broadcasting and sending output from CD or digital media players to radios without auxiliary-in jacks, though this is illegal in some other countries. This practice was legalised in the United Kingdom on 8 December 2006. ELF 3 Hz/100 Mm 30 Hz/10 Mm SLF 30 Hz/10 Mm 300 Hz/1 Mm ULF 300 Hz/1 Mm 3 kHz/100 km VLF 3 kHz/100 km 30 kHz/10 km LF 30 kHz/10 km 300 kHz/1 km MF 300 kHz/1 km 3 MHz/100 m HF 3 MHz/100 m 30 MHz/10 m VHF 30 MHz/10 m 300 MHz/1 m UHF 300 MHz/1 m 3 GHz/100 mm SHF 3 GHz/100 mm 30 GHz/10 mm EHF 30 GHz/10 mm 300 GHz/1 mm THF 300 GHz/1 mm 3 THz/0.1 mm Sensors A sensor

1260-558: Is less of a problem in this and higher frequency bands than at lower frequencies. The VHF band is the first band at which efficient transmitting antennas are small enough that they can be mounted on vehicles and portable devices, so the band is used for two-way land mobile radio systems , such as walkie-talkies , and two way radio communication with aircraft ( Airband ) and ships ( marine radio ). Occasionally, when conditions are right, VHF waves can travel long distances by tropospheric ducting due to refraction by temperature gradients in

1323-739: Is measured; making the sensor smaller often improves this and may introduce other advantages. Technological progress allows more and more sensors to be manufactured on a microscopic scale as microsensors using MEMS technology. In most cases, a microsensor reaches a significantly faster measurement time and higher sensitivity compared with macroscopic approaches. Due to the increasing demand for rapid, affordable and reliable information in today's world, disposable sensors—low-cost and easy‐to‐use devices for short‐term monitoring or single‐shot measurements—have recently gained growing importance. Using this class of sensors, critical analytical information can be obtained by anyone, anywhere and at any time, without

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1386-680: Is modeled after the point-to-point telex network, all messages come to a central processing location to be routed. ARINC and SITA are the two primary service providers, with smaller operations from others in some areas. Some areas have multiple service providers. ACARS messages may be of three broad types: Control messages are used to communicate between the aircraft and its base, with messages either standardized according to ARINC Standard 633, or user-defined in accordance with ARINC Standard 618. The contents of such messages can be OOOI events, flight plans, weather information, equipment health, status of connecting flights, etc. A major function of ACARS

1449-469: Is not used for television services in or near Sydney, Melbourne, Brisbane, Adelaide or Perth, digital radio in those cities are broadcast on DAB frequencies blocks 9A, 9B and 9C. VHF radio is also used for marine Radio as per its long-distance reachability comparing UHF frequencies. Example allocation of VHF–UHF frequencies: Until 2013, the four main free-to-air TV stations in New Zealand used

1512-403: Is referred to as sensor or nanosensor . This terminology applies for both in-vitro and in vivo applications. The encapsulation of the biological component in biosensors, presents a slightly different problem that ordinary sensors; this can either be done by means of a semipermeable barrier , such as a dialysis membrane or a hydrogel , or a 3D polymer matrix, which either physically constrains

1575-612: Is reserved for displaced class D stations which have no other frequencies in the normal 88.1–107.9 MHz subband to move to. So far, only two stations have qualified to operate on 87.9 MHz: 10–watt KSFH in Mountain View, California and 34–watt translator K200AA in Sun Valley, Nevada . In some countries, particularly the United States and Canada, limited low-power license-free operation

1638-570: Is the basis for modern image sensors , including the charge-coupled device (CCD) and the CMOS active-pixel sensor (CMOS sensor), used in digital imaging and digital cameras . Willard Boyle and George E. Smith developed the CCD in 1969. While researching the MOS process, they realized that an electric charge was the analogy of the magnetic bubble and that it could be stored on a tiny MOS capacitor. As it

1701-410: Is to automatically detect and report the start of each major flight phase, called OOOI events in the industry ( o ut of the gate, o ff the ground, o n the ground, and i nto the gate). These OOOI events are detected using input from aircraft sensors mounted on doors, parking brakes, and struts. At the start of each flight phase, an ACARS message is transmitted to the ground describing the flight phase,

1764-742: The HF band there is only some reflection at lower frequencies from the ionosphere ( skywave propagation). They do not follow the contour of the Earth as ground waves and so are blocked by hills and mountains, although because they are weakly refracted (bent) by the atmosphere they can travel somewhat beyond the visual horizon out to about 160 km (100 miles). They can penetrate building walls and be received indoors, although in urban areas reflections from buildings cause multipath propagation , which can interfere with television reception. Atmospheric radio noise and interference ( RFI ) from electrical equipment

1827-619: The Yagi antenna is the most widely used as a high gain or "beam" antenna. For television reception, the Yagi is used, as well as the log-periodic antenna due to its wider bandwidth. Helical and turnstile antennas are used for satellite communication since they employ circular polarization . For even higher gain, multiple Yagis or helicals can be mounted together to make array antennas . Vertical collinear arrays of dipoles can be used to make high gain omnidirectional antennas , in which more of

1890-534: The gas sensor FET (GASFET), surface accessible FET (SAFET), charge flow transistor (CFT), pressure sensor FET (PRESSFET), chemical field-effect transistor (ChemFET), reference ISFET (REFET), biosensor FET (BioFET), enzyme-modified FET (ENFET) and immunologically modified FET (IMFET). By the early 2000s, BioFET types such as the DNA field-effect transistor (DNAFET), gene-modified FET (GenFET) and cell-potential BioFET (CPFET) had been developed. MOS technology

1953-597: The visual horizon out to about 160 km (100 miles). Common uses for radio waves in the VHF band are Digital Audio Broadcasting (DAB) and FM radio broadcasting, television broadcasting , two-way land mobile radio systems (emergency, business, private use and military), long range data communication up to several tens of kilometers with radio modems , amateur radio , and marine communications . Air traffic control communications and air navigation systems (e.g. VOR and ILS ) work at distances of 100 kilometres (62 miles) or more to aircraft at cruising altitude. In

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2016-435: The 10 VHF channels were insufficient to support the growth of television services. This was rectified by the addition of three additional frequencies-channels 0, 5A and 11. Older television sets using rotary dial tuners required adjustment to receive these new channels. Most TVs of that era were not equipped to receive these broadcasts, and so were modified at the owners' expense to be able to tune into these bands; otherwise

2079-541: The 625-line colour signal), with the exception of BBC2 (which had always broadcast solely on UHF). The last British VHF TV transmitters closed down on January 3, 1985. VHF band III is now used in the UK for digital audio broadcasting , and VHF band II is used for FM radio , as it is in most of the world. Unusually, the UK has an amateur radio allocation at 4 metres , 70–70.5 MHz. Frequency assignments between US and Canadian users are closely coordinated since much of

2142-490: The ACARS unit of a South African Airways flight from Johannesburg 's OR Tambo International Airport to Brussels sent an ACARS message about an “alpha floor event”, which was activated when the Airbus A340-600's envelope protection system activated to override the pilots to prevent the plane from stalling on take-off. On 19 February 2023, there were numerous ACARS reports of a large white balloon near Hawaii in

2205-458: The Americas and many other parts of the world, VHF Band I was used for the transmission of analog television . As part of the worldwide transition to digital terrestrial television most countries require broadcasters to air television in the VHF range using digital, rather than analog encoding. Radio waves in the VHF band propagate mainly by line-of-sight and ground-bounce paths; unlike in

2268-557: The Canadian population is within VHF radio range of the US border. Certain discrete frequencies are reserved for radio astronomy . The general services in the VHF band are: Cable television , though not transmitted aerially, uses a spectrum of frequencies overlapping VHF. The U.S. FCC allocated television broadcasting to a channelized roster as early as 1938 with 19 channels. That changed three more times: in 1940 when Channel 19

2331-615: The FMS while in flight, and allows the flight crew to evaluate new weather conditions or alternative flight plans. ACARS is used to send information from the aircraft to ground stations about the conditions of various aircraft systems and sensors in real-time. Maintenance faults and abnormal events are also transmitted to ground stations along with detailed messages, which are used by the airline for monitoring equipment health, and to better plan repair and maintenance activities. Automated ping messages are used to test an aircraft's connection with

2394-471: The VHF television bands ( Band I and Band III ) to transmit to New Zealand households. Other stations, including a variety of pay and regional free-to-air stations, were forced to broadcast in the UHF band, since the VHF band had been very overloaded with four stations sharing a very small frequency band, which was so overcrowded that one or more channels would not be available in some smaller towns. However, at

2457-545: The aircraft lanes. In 2002, ACARS was added to the NOAA Observing System Architecture . Thus commercial aircraft can act as weather data providers for weather agencies to use in their forecast models, sending meteorological observations like winds and temperatures over the ACARS network. NOAA provides real-time weather maps. VHF Very high frequency ( VHF ) is the ITU designation for

2520-438: The aircraft was airborne or not, and if on the ground whether it was at the gate or not. The flight crews reported these times by voice to geographically dispersed radio operators. Airlines wanted to eliminate self-reported times to preclude inaccuracies, whether accidental or deliberate. Doing so also reduced the need for human radio operators to receive the reports. In an effort to reduce crew workload and improve data integrity,

2583-460: The antenna's power is radiated in horizontal directions. Television and FM broadcasting stations use collinear arrays of specialized dipole antennas such as batwing antennas . Certain subparts of the VHF band have the same use around the world. Some national uses are detailed below. The VHF TV band in Australia was originally allocated channels 1 to 10-with channels 2, 7 and 9 assigned for

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2646-427: The atmosphere. VHF transmission range is a function of transmitter power, receiver sensitivity, and distance to the horizon, since VHF signals propagate under normal conditions as a near line-of-sight phenomenon. The distance to the radio horizon is slightly extended over the geometric line of sight to the horizon, as radio waves are weakly bent back toward the Earth by the atmosphere. An approximation to calculate

2709-557: The base, and in innumerable applications of which most people are never aware. With advances in micromachinery and easy-to-use microcontroller platforms, the uses of sensors have expanded beyond the traditional fields of temperature, pressure and flow measurement, for example into MARG sensors . Analog sensors such as potentiometers and force-sensing resistors are still widely used. Their applications include manufacturing and machinery, airplanes and aerospace, cars, medicine, robotics and many other aspects of our day-to-day life. There

2772-431: The communication station. In the event that the aircraft ACARS unit has been silent for longer than a preset time interval, the ground station can ping the aircraft (directly or via satellite). A ping response indicates a healthy ACARS communication. ACARS interfaces with interactive display units in the cockpit, which flight crews can use to send and receive technical messages and reports to or from ground stations, such as

2835-473: The end of 2013 , all television channels stopped broadcasting on the VHF bands, as New Zealand moved to digital television broadcasting, requiring all stations to either broadcast on UHF or satellite (where UHF was unavailable) utilising the Freeview service. Refer to Australasian television frequencies for more information. British television originally used VHF band I and band III . Television on VHF

2898-475: The engineering department at ARINC introduced the ACARS system in July 1978, as an automated time clock system. Teledyne Controls produced the avionics and the launch customer was Piedmont Airlines . The original expansion of the abbreviation was "Arinc Communications Addressing and Reporting System". Later, it was changed to "Aircraft Communications, Addressing and Reporting System". The original avionics standard

2961-499: The expense of the dynamic behavior of the sensor. The sensor resolution or measurement resolution is the smallest change that can be detected in the quantity that is being measured. The resolution of a sensor with a digital output is usually the numerical resolution of the digital output. The resolution is related to the precision with which the measurement is made, but they are not the same thing. A sensor's accuracy may be considerably worse than its resolution. A chemical sensor

3024-565: The initial services in Sydney and Melbourne , and later the same channels were assigned in Brisbane , Adelaide and Perth . Other capital cities and regional areas used a combination of these and other frequencies as available. The initial commercial services in Hobart and Darwin were respectively allocated channels 6 and 8 rather than 7 or 9. By the early 1960s it became apparent that

3087-408: The line-of-sight horizon distance (on Earth) is: These approximations are only valid for antennas at heights that are small compared to the radius of the Earth. They may not necessarily be accurate in mountainous areas, since the landscape may not be transparent enough for radio waves. In engineered communications systems, more complex calculations are required to assess the probable coverage area of

3150-400: The major airlines until the 1980s. Early ACARS systems were extended over the years to support aircraft with digital data bus interfaces, flight management systems , and thermal printers . ACARS as a term refers to the complete air and ground system, consisting of equipment on board, equipment on the ground, and a service provider. On-board ACARS equipment consists of end systems with

3213-409: The need for recalibration and worrying about contamination. A good sensor obeys the following rules: Most sensors have a linear transfer function . The sensitivity is then defined as the ratio between the output signal and measured property. For example, if a sensor measures temperature and has a voltage output, the sensitivity is constant with the units [V/K]. The sensitivity is the slope of

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3276-406: The open-gate field-effect transistor (OGFET) introduced by Johannessen in 1970, the ion-sensitive field-effect transistor (ISFET) invented by Piet Bergveld in 1970, the adsorption FET (ADFET) patented by P.F. Cox in 1974, and a hydrogen -sensitive MOSFET demonstrated by I. Lundstrom, M.S. Shivaraman, C.S. Svenson and L. Lundkvist in 1975. The ISFET is a special type of MOSFET with a gate at

3339-526: The owner had to buy a new TV. Several TV stations were allocated to VHF channels 3, 4 and 5, which were within the FM radio bands although not yet used for that purpose. A couple of notable examples were NBN-3 Newcastle , WIN-4 Wollongong and ABC Newcastle on channel 5. While some Channel 5 stations were moved to 5A in the 1970s and 80s, beginning in the 1990s, the Australian Broadcasting Authority began

3402-466: The range of radio frequency electromagnetic waves ( radio waves ) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF are denoted high frequency (HF), and the next higher frequencies are known as ultra high frequency (UHF). VHF radio waves propagate mainly by line-of-sight , so they are blocked by hills and mountains, although due to refraction they can travel somewhat beyond

3465-521: The recognition step, analyte molecules interact selectively with receptor molecules or sites included in the structure of the recognition element of the sensor. Consequently, a characteristic physical parameter varies and this variation is reported by means of an integrated transducer that generates the output signal. A chemical sensor based on recognition material of biological nature is a biosensor . However, as synthetic biomimetic materials are going to substitute to some extent recognition biomaterials,

3528-665: The sensing macromolecule or chemically constrains the macromolecule by bounding it to the scaffold. Neuromorphic sensors are sensors that physically mimic structures and functions of biological neural entities. One example of this is the event camera . The MOSFET invented at Bell Labs between 1955 and 1960, MOSFET sensors (MOS sensors) were later developed, and they have since been widely used to measure physical , chemical , biological and environmental parameters. A number of MOSFET sensors have been developed, for measuring physical , chemical , biological , and environmental parameters. The earliest MOSFET sensors include

3591-412: The time at which it occurred, and other related information such as the amount of fuel on board or the flight origin and destination. These messages are used to track the status of aircraft and crews. ACARS interfaces with flight management systems (FMS), acting as the communication system for flight plans and weather information to be sent from the ground to the FMS. This enables the airline to update

3654-459: The transfer function. Converting the sensor's electrical output (for example V) to the measured units (for example K) requires dividing the electrical output by the slope (or multiplying by its reciprocal). In addition, an offset is frequently added or subtracted. For example, −40 must be added to the output if 0 V output corresponds to −40 C input. For an analog sensor signal to be processed or used in digital equipment, it needs to be converted to

3717-636: Was ARINC 597, which defined an ACARS Management Unit consisting of discrete inputs for the doors, parking brake and weight on wheels sensors to automatically determine the flight phase and generate and send as telex messages. It also contained a MSK modem , which was used to transmit the reports over existing VHF voice radios. Global standards for ACARS were prepared by the Airlines Electronic Engineering Committee (AEEC). The first day of ACARS operations saw about 4,000 transactions, but it did not experience widespread use by

3780-406: Was deleted and several channels changed frequencies, then in 1946 with television going from 18 channels to 13 channels, again with different frequencies, and finally in 1948 with the removal of Channel 1 (analog channels 2–13 remain as they were, even on cable television ). Channels 14–19 later appeared on the UHF band, while channel 1 remains unused. 87.5–87.9 MHz

3843-435: Was discussion about making ACARS an "online- black-box " to reduce the effects of the loss of a flight recorder. However no changes were made to the ACARS system. In March 2014, ACARS messages and Doppler analysis of ACARS satellite communication data played a very significant role in efforts to trace Malaysia Airlines Flight 370 to an approximate location. While the primary ACARS system on board MH370 had been switched off,

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3906-431: Was fairly straightforward to fabricate a series of MOS capacitors in a row, they connected a suitable voltage to them so that the charge could be stepped along from one to the next. The CCD is a semiconductor circuit that was later used in the first digital video cameras for television broadcasting . The MOS active-pixel sensor (APS) was developed by Tsutomu Nakamura at Olympus in 1985. The CMOS active-pixel sensor

3969-399: Was in black and white with 405-line format (although there were experiments with all three colour systems- NTSC , PAL , and SECAM -adapted for the 405-line system in the late 1950s and early 1960s). British colour television was broadcast on UHF (channels 21–69), beginning in the late 1960s. From then on, TV was broadcast on both VHF and UHF (VHF being a monochromatic downconversion from

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