Transponder X2

[Brigitta Martini]

In air navigation or radio frequency identification, a flight transponder is an automated transceiver in an aircraft that emits a coded identifying signal in response to an interrogating received signal.

In a communications satellite, a satellite transponder receives signals over a range of uplink frequencies, usually from a satellite ground station; the transponder amplifies them, and re-transmits them on a different set of downlink frequencies to receivers on Earth, often without changing the content of the received signal or signals.

In fiber-optic communications, a transponder is the element that sends and receives the optical signal from a fiber. A transponder is typically characterized by its data rate and the maximum distance the signal can travel.

Another type of transponder occurs in identification friend or foe (IFF) systems in military aviation and in air traffic control secondary surveillance radar (beacon radar) systems for general aviation and commercial aviation.[7]

Primary radar works best with large all-metal aircraft, but not so well on small, composite aircraft. Its range is also limited by terrain and rain or snow and also detects unwanted objects such as automobiles, hills and trees. 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.[citation needed]

Depending on the type of interrogation, the transponder sends back a transponder code (or "squawk code", Mode A) or altitude information (Mode C) to help air traffic controllers to identify the aircraft and to maintain separation between planes. Another mode called Mode S (Mode Select) is designed to help avoiding over-interrogation of the transponder (having many radars in busy areas) and to allow automatic collision avoidance. Mode S transponders are backward compatible with Modes A and C. Mode S is mandatory in controlled airspace in many countries. Some countries have also required, or are moving toward requiring, that all aircraft be equipped with Mode S, even in uncontrolled airspace. However, in the field of general aviation there have been objections to these moves, because of the cost, size, limited benefit to the users in uncontrolled airspace, and, in the case of balloons and gliders, the power requirements during long flights.[citation needed]

The International Maritime Organization's International Convention for the Safety of Life at Sea (SOLAS) requires the Automatic Identification System (AIS) to be fitted aboard international voyaging ships with 300 or more gross tonnage (GT), and all passenger ships regardless of size.[9] AIS transmitters/receivers are generally called transponders, but they generally transmit autonomously, although coast stations can interrogate class B transponders on smaller vessels for additional information.[citation needed] In addition, navigational aids often have transponders called RACON (radar beacons) designed to make them stand out on a ship's radar screen.[citation needed]

Transponders are used in races for lap timing. A cable loop is dug into the race circuit near to the start/finish line. Each individual runner or car has an active transponder with a unique ID code. When the individual passes the start/finish line, the lap time and the racing position is shown on the score board.[citation needed]

Passive and active RFID systems are used in motor sports, and off-road events such as Enduro and Hare and Hounds racing, the riders have a transponder on their person, normally on their arm. When they complete a lap they swipe or touch the receiver which is connected to a computer and log their lap time.[citation needed]

NASCAR uses transponders and cable loops placed at numerous points around the track to determine the lineup during a caution period. This system replaced a dangerous race back to the start-finish line.[citation needed]

Many modern automobiles have keys with transponders hidden inside the plastic head of the key. The user of the car may not even be aware that the transponder is there, because there are no buttons to press. When a key is inserted into the ignition lock cylinder and turned, the car's computer sends a signal to the transponder. Unless the transponder replies with a valid code, the computer will not allow the engine to be started. Transponder keys have no battery; they are energized by the signal itself.[10][11]

Transponders may also be used by residents to enter their gated communities.[citation needed] However, having more than one transponder causes problems. If a resident's car with simple transponder is parked in the vicinity, any vehicle can come up to the automated gate, triggering the gate interrogation signal, which may get an acceptable response from the resident's car. Such units properly installed might involve beamforming, unique transponders for each vehicle, or simply obliging vehicles to be stored away from the gate.[citation needed]

Transponders are typically used for detecting, identifying and locating objects, but they can also be used in other technologies, such as in satellites to relay communications signals. Transponders are commonly found in both civilian and military aircraft and in objects, such as car keys.

When sent a signal -- also called an interrogator -- a transponder responds by returning an identifying signal. The information included in the response varies depending on the type of transponder but can include location and identifying codes. The transponder automatically sends back a radio signal at a predetermined frequency. To receive and send signals simultaneously, receiving and transmitting signals must be set at different frequencies.

An air traffic controller can send an interrogator signal and receive identifying information on an aircraft. This enables the control tower to track the aircraft in the surrounding airspace and provide other information to help the pilots maintain adequate distance from other aircraft.

Transponders can be integrated into chipped car keys. When a transponder key is inserted or a key fob is pushed, a receiver in the ignition's circuitry picks up the signal. If the transponder's serial number matches the car's programmed number, the vehicle starts when the user inserts the key or pushes the start button.

Electronic toll collection systems use transponders mounted on vehicle windshields or license plate readers to enable cashless toll collection. For example, the Florida Turnpike uses prepaid accounts, such as SunPass and E-PASS, to collect tolls on toll roads and bridges throughout the state. This eliminates the need for manned tollbooths.

Transponders can be either passive or active. A passive transponder enables a computer or robot to identify an object. Magnetic labels -- such as those on credit cards and store items -- are common examples. A passive transponder must be used with an active sensor that decodes and transcribes the data the transponder contains. The transponder unit can be physically tiny, and its information can be sensed up to several feet away.

Simple active transponders are employed in location, identification and navigation systems for commercial and private aircraft. An example is a radio frequency identification (RFID) device that transmits a coded signal when it receives a request from a monitoring or control point. The transponder output signal is tracked, so the position of the transponder can be constantly monitored. The input (receiver) and output (transmitter) frequencies are pre-assigned. Transponders of this type can operate over distances of thousands of miles.

Sophisticated active transponders are used in communications satellites and on board space vehicles. They receive incoming signals over a range -- or band -- of frequencies and retransmit the signals on a different band at the same time. The device is similar to the type of repeater used in land-based cellular telephone networks. The incoming signal, usually originating from a point on the Earth's surface, is called the uplink. The outgoing signal, usually sent to a point or region on the surface, is called the downlink. These transponders sometimes operate on an interplanetary scale.

The Toll Roads offer a variety of transponders to best fit the needs of our drivers. Whether you have a sticker or switchable, all transponders issued by The Toll Roads can be used to pay tolls on any tolled bridge, lanes and road throughout California.

You can request sticker transponders or purchase FasTrak Flex switchable transponders by logging into your account at TheTollRoads.com or The Toll Roads app, by calling our Customer Service Call Center, by visiting one of our Customer Service Walk-In Centers or by purchasing toll credits at one of our retail partners.

Prior to starting each trip, it is the driver's responsibility to indicate the number of occupants in the vehicle by moving the switch to the appropriate setting (1, 2, 3+). Some tolling facilities allow qualifying carpools and eligible vehicles to drive for free or at a discounted rate. The Toll Roads do not offer carpool discounts, but FasTrak accountholders may be eligible for a frequent driver discount.

Motorcycle transponders are sticker transponders made specifically for motorcycles. They can be mounted to the headlamp lens or cover. If you have a motorcycle listed on your account, you can request a motorcycle sticker transponder by calling our Customer Service Call Center at 949-727-4800.

Renewing a transponder means paying the annual user fee for a vehicle that already has a transponder and for which the annual user fee was paid in some earlier year. A new transponder is provided only for certain reasons.

The DTOPS website lets you place orders and pay online for Annual User Fees (Commercial Vehicles, Private Vessels, and Private Aircraft) and Single Crossing Fees (Commercial Vehicles) associated with crossing the border into the United States. Transponders are used for commercial vehicles while decals are used for private aircraft and private vessels (30 ft+). Single crossing fees apply only to commercial vehicles.

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