Transponder
Encyclopedia
Telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
, the term transponder (short-for Transmitter-responder and sometimes abbreviated to XPDR, XPNDR, TPDR or TP) has the following meanings:
- An automaticAutomatic- Technology :* Automatic transmission, or a car with an automatic transmission* Automatic firearm* Automatic watch* Automatic , a defunct American automobile company- Albums :* Automatic * Automatic...
deviceInformation applianceIn general terms, an information appliance or information device is any machine or device that is usable for the purposes of computing, telecommunicating, reproducing, and presenting encoded information in myriad forms and applications....
that receivesReceiver (radio)A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
, amplifiesAmplifierGenerally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
, and retransmitsTransmission (telecommunications)Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
a signal on a different frequencyFrequencyFrequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
(see also broadcast translator). - An automatic device that transmits a predetermined messageMessageA message in its most general meaning is an object of communication. It is a vessel which provides information. Yet, it can also be this information. Therefore, its meaning is dependent upon the context in which it is used; the term may apply to both the information and its form...
in response to a predefined received signal. - A receiver-transmitterTransceiverA transceiver is a device comprising both a transmitter and a receiver which are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter-receiver. The term originated in the early 1920s...
that will generate a reply signal upon proper electronic interrogation.
Satellite/broadcast communications
A communications satelliteCommunications satellite
A communications satellite is an artificial satellite stationed in space for the purpose of telecommunications...
’s channels
Channel (communications)
In telecommunications and computer networking, a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel...
are called transponders, because each is a separate transceiver
Transceiver
A transceiver is a device comprising both a transmitter and a receiver which are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter-receiver. The term originated in the early 1920s...
or repeater
Repeater
A repeater is an electronic device that receives asignal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.-Description:...
. With digital video
Digital video
Digital video is a type of digital recording system that works by using a digital rather than an analog video signal.The terms camera, video camera, and camcorder are used interchangeably in this article.- History :...
data compression
Data compression
In computer science and information theory, data compression, source coding or bit-rate reduction is the process of encoding information using fewer bits than the original representation would use....
and multiplexing
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
, several video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
and audio channels may travel through a single transponder on a single wideband
Wideband
In communications, wideband is a relative term used to describe a wide range of frequencies in a spectrum. A system is typically described as wideband if the message bandwidth significantly exceeds the channel's coherence bandwidth....
carrier
Carrier wave
In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
. Original analog video only has one channel per transponder, with subcarrier
Subcarrier
A subcarrier is a separate analog or digital signal carried on a main radio transmission, which carries extra information such as voice or data. More technically, it is an already-modulated signal, which is then modulated into another signal of higher frequency and bandwidth...
s for audio and automatic transmission identification service (ATIS
Automatic Transmitter Identification System
The Automatic Transmitter Identification System is a communications protocol used for the station identification of television channels carried on satellite TV....
). Non-multiplexed radio station
Radio station
Radio broadcasting is a one-way wireless transmission over radio waves intended to reach a wide audience. Stations can be linked in radio networks to broadcast a common radio format, either in broadcast syndication or simulcast or both...
s can also travel in single channel per carrier
Single channel per carrier
Single channel per carrier refers to using a single signal at a given frequency and bandwidth. Most often, this is used on broadcast satellites to indicate that radio stations are not multiplexed as subcarriers onto a single video carrier, but instead independently share a transponder...
(SCPC) mode, with multiple carriers (analog or digital) per transponder. This allows each station to transmit directly to the satellite, rather than paying for a whole transponder, or using landline
Landline
A landline was originally an overland telegraph wire, as opposed to an undersea cable. Currently, landline refers to a telephone line which travels through a solid medium, either metal wire or optical fibre, as distinguished from a mobile cellular line, where transmission is via radio waves...
s to send it to an earth station for multiplexing with other stations.
Optical communications
In optical fiber communications, a transponder is the element that sends and receives the optical signal from a fiberFiber
Fiber is a class of materials that are continuous filaments or are in discrete elongated pieces, similar to lengths of thread.They are very important in the biology of both plants and animals, for holding tissues together....
. A transponder is typically characterized by its data rate and the maximum distance the signal can travel.
Different descriptions, with important functional differences, might be implicitly assumed across various academic and commercial literature:
- according to one description, a transponder and transceiverTransceiverA transceiver is a device comprising both a transmitter and a receiver which are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter-receiver. The term originated in the early 1920s...
are both functionally similar devices that convert a full-duplex electrical signal in a full-duplex optical signal. The difference between the two being that transceivers interface electrically with the host system using a serial 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 and consume more power than transceivers. - according to another description, transceivers are limited to providing an electrical-optical function only (not differentiating between serial or parallel electrical interfaces), whereas transponders convert an optical signal at one wavelengthWavelengthIn physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
to an optical signal at another wavelength (typically ITU standardizedFrequency gridThe most common frequency grid is that used for channel spacing in Dense Wavelength Division Multiplexing for Fiber-optic communication at wavelengths around 1550 nm and defined by ITU-T G.694.1 . The grid is defined relative to 193.1THz and extends from 191.7 THz to 196.1 THz with...
for DWDM communication). As such, transponders can be considered as two transceivers placed back-to-back. This view also seems to be held by e.g. FujitsuFujitsuis a Japanese multinational information technology equipment and services company headquartered in Tokyo, Japan. It is the world's third-largest IT services provider measured by revenues....
As a result, difference in transponder functionality also might influence the functional description of related optical modules like transceivers and muxponder
Muxponder
- Optical communications:In optical fiber communications, a muxponder is the element that sends and receives the optical signal on a fiber in much the same way as a transponder except that the muxponder has the additional functionality of multiplexing multiple sub-rate client interfaces onto the...
s.
Aviation
Another type of transponder occurs in identification friend or foeIdentification friend or foe
In telecommunications, identification, friend or foe is an identification system designed for command and control. It is a system that enables military and national interrogation systems to identify aircraft, vehicles, or forces as friendly and to determine their bearing and range from the...
systems in military aviation and in air traffic control
Air traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...
secondary surveillance radar
Secondary surveillance radar
Secondary surveillance radar is a radar system used in air traffic control , that not only detects and measures the position of aircraft i.e. range and bearing, but also requests additional information from the aircraft itself such as its identity and altitude...
(beacon radar) systems for general aviation
General aviation
General aviation is one of the two categories of civil aviation. It refers to all flights other than military and scheduled airline and regular cargo flights, both private and commercial. General aviation flights range from gliders and powered parachutes to large, non-scheduled cargo jet flights...
and commercial aviation
Commercial aviation
Commercial aviation is the part of civil aviation that involves operating aircraft for hire to transport passengers or cargo...
. Primary radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
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.
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. Another mode called Mode S (Mode Select) is designed to help avoiding overinterogation of the transponder (having many radars in busy areas) and to allow automatic collision avoidance. Mode S transponders are 'backwards compatible' with Modes A & C. Mode S is mandatory in controlled airspace in many countries. Some countries have also required, or are moving towards requiring, that all aircraft be equipped with Mode S, even in uncontrolled airspace. However in the field of general aviation
General aviation
General aviation is one of the two categories of civil aviation. It refers to all flights other than military and scheduled airline and regular cargo flights, both private and commercial. General aviation flights range from gliders and powered parachutes to large, non-scheduled cargo jet flights...
, 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
Glider (sailplane)
A glider or sailplane is a type of glider aircraft used in the sport of gliding. Some gliders, known as motor gliders are used for gliding and soaring as well, but have engines which can, in some cases, be used for take-off or for extending a flight...
, the power requirements during long flights.
Marine
Navigational aids often have transponders called RACONRacon
A racon is a radar transponder commonly used to mark maritime navigational hazards. The word is a portmanteau of RAdar and beaCON.When a racon receives a radar pulse, it responds with a signal on the same frequency which puts an image on the radar display...
designed to make them stand out on a ship's radar screen.
Automotive
Many modern automobiles (especially the more expensive models) have keys with transponders hidden inside the plastic head of the key. The owner 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 radio 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 radio signal itself.Road
The E-ZPassE-ZPass
E-ZPass is an electronic toll-collection system used on most tolled roads, bridges, and tunnels in the northeastern US, south to Virginia and West Virginia, and west to Illinois. Currently, there are 25 agencies spread across 14 states that make up the . All member agencies use the same technology,...
system in the eastern United States is one of many systems for paying bridge and road tolls by a RFID transponder in the car. The Highway 407 in Ontario is one of the world's first completely automated toll highways.
Motorsport
Transponders are used in motorsport for lap timing purposes. A cable loop is dug into the race circuit near to the start/finish line. Each car has an active transponder with a unique id code. When the racing car passes the start/finish line the lap time and the racing position is shown on the score board.Passive and active RFID systems are used in off road events such as Enduro
Enduro
Enduro is a form of motorcycle sport run on courses that are predominantly off-road. Enduro consists of many different obstacles and challenges...
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. The Casimo Group Ltd make a system which does this.
NASCAR
NASCAR
The National Association for Stock Car Auto Racing is a family-owned and -operated business venture that sanctions and governs multiple auto racing sports events. It was founded by Bill France Sr. in 1947–48. As of 2009, the CEO for the company is Brian France, grandson of the late Bill France Sr...
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
Racing back to the caution
In automobile racing, specifically NASCAR stock car racing, "racing back to the caution" is a term used to describe a procedure about what drivers did after a caution flag was displayed.-NASCAR usage:...
.
Underwater
SonarSonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...
transponders operate under water and are used to measure distance and form the basis of underwater location marking, position tracking and navigation
Navigation
Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...
.
Gated communities
Transponders may also be used by residents to enter their gated communitiesGated community
In its modern form, a gated community is a form of residential community or housing estate containing strictly-controlled entrances for pedestrians, bicycles, and automobiles, and often characterized by a closed perimeter of walls and fences. Gated communities usually consist of small residential...
. However, having more than one transponder causes problems.
External links
- Transponding with DCC - Transponding in model railroading.