Transponder ( transponder from trans mitter-res ponder "transmitter-responder") or radio transceiver - a transceiver device that sends a signal in response to a received signal , for example:
- an automatic device that receives , amplifies and further transmits a signal at a different frequency , for example, a digital cable television transponder ( DVB-C ).
- an automatic device that transmits a predetermined message in response to a predetermined received signal;
- a transceiver that always generates a response signal with the correct electronic request.
Content
Use
Satellite communication channels are formed using transponders - this is usually a transceiver ( transceiver ) or a repeater ( repeater ).
In cable television, an analogue of an on - air transmitter is called a transponder, but it transmits a signal to a viewer through a cable. There are also transponders acting as a multi-signal television cable television signal meter.
When using digital compression and multiplexing of signals, several audio and video streams can be transmitted through one transponder at the same frequency. Initially, analog video signals were transmitted over a single channel to a transponder - with subcarriers for audio tracks and the Automatic Transmission Identification Service ( ATIS ).
Identification systems in secondary radar and identification of "friend or foe" . Transponders are used in aviation to recognize signals on the radar screen. Most aircraft transponders are capable of transmitting information about the type, altitude and speed of the aircraft and the 4-digit transponder identification code ( squawk code ) assigned by the ATC unit.
Transponders for finding skiers littered with snow ( beeper ), transponders for finding home keys (the transponder gives a signal to the user's whistle).
Sonar transponders operate under water and are used to measure the distance to objects.
In automobile transport, transponders are often used to quickly travel special payment points on toll roads , parking lots, etc.
Also, transponders are used in the ever-growing RFID technology . In RFID technology - radio frequency identification, transponders play the role of an identifier for an object (in warehouses, libraries, etc.)
The WDM transponder (CWDM, DWDM) allows you to convert the wavelength of the signal received from the transceiver into a wavelength that complies with the ITU-T G.692 recommendations (channel spacing 0.8-1 nm).
Civil Aviation Transponder
Transponders mounted on board an aircraft , used for identification by an air traffic controller of an aircraft. They respond to the request of the secondary locator of the dispatching service with a four-digit code. This code ( squawk code ) is preliminarily issued by the dispatcher and set by the pilot on the transponder control panel (if the dispatcher did not give the pilot a code, then the standard code is set: 7000 - flight code for Europe and 1200 - flight code for America.) The controller on the monitor the locator sees a mark on the position of the aircraft, along with the code. A transponder capable of delivering only a four-digit code is mode A.
There are several special codes ( squawk code ):
7700 - an accident or other catastrophic situation on board
7600 - loss of connection
7500 - aircraft capture
In this case, a notification is automatically turned on in the dispatching service when the code data is displayed on the radar screen, drawing the attention of the service.
A significant problem when using mode A transponders is the lack of information about the altitude of the aircraft. To solve this situation, mode C was created. It complements the four-digit code information with barometric altitude data for standard pressure without correction.
Mode A + C transponders are sometimes called RBS . In the United States, they are mandatory for flights above 10,000 feet (3 km) and within 30 miles around large airports.
More intelligent is the mode S transponder. Its main feature is the control over the air and data transfer only when it is free. This allows you to solve the problem of clogging of the air in the area with an increased number of boards (for example, in the airport area). These transponders are additionally broadcast: on-board number, call sign, serial number of the transponder, aircraft altitude, speed and GPS coordinates.
Mode S transponders come in two forms: ELS (ELementary Surveillance) and EHS (EnHanced Surveillance). ELS and EHS differ in the set of transmitted parameters. In Europe, at least ELS is required, and in the upper airspace for heavy aircraft - EHS.
The next step in development is the TCAS ( traffic collision avoidance system ) device, which combines a radar and a transponder. TCAS displays on-board aircraft radar information about the surrounding sides with transponders. He is also able, based on the information received, to give the pilot a warning about dangerous proximity with other sides and give a command on how to change the trajectory of movement to avoid a collision. For this, a transponder of at least C mode must be installed on other sides.
Operating frequency for transponders of modes A, C, S: 1090 MHz
Space Transponders
The spacecraft (SC) used to transmit television , radio , Internet and space communications transponders are used in the C, Ku, Ka bands .
A specific feature of the use of transponders in spacecraft is the limitation in power and frequency range, which is associated with the limited power of solar panels on the spacecraft. Transponders on spacecraft can be with signal processing and without processing (only re-emission at a different frequency).
On one spacecraft can be up to several tens of transponders [1] .
Cable Transponder
A digital television cable transponder transmits a multiplex of several channels at a specific frequency. A DVB-C standard digital cable receiver finds these multiplexes and tunes in them. Modern TVs support the DVB-C standard without an additional receiver.
A television cable transponder can also be used to measure the level of television channels with analog or digital modulation . For a television signal of standards DVB-T / T2 / C allows you to measure reception quality indicators - the modulation error rate of the digital stream MER, the frequency of occurrence of erroneous BER bits to the Viterbi decoder ( DVB-T standard) or LDPC ( DVB-T2 standard), as well as and after the Reed-Solomon decoder ( BCH for DVB-T2). The module provides a mode of automatic determination of modulation parameters of digital TV signals and control of executive devices at the facility by commands from a remote control panel.
The television measuring cable transponder is a DVB-T / T2 / C standard signal receiver with signal demodulation to the MPEG-2 transport stream. The input tuner is a dual-frequency superheterodyne receiver with automatic frequency tuning. The MER modulation error rate is measured during demodulation of a QAM or OFDM signal based on vector analysis . The error rate of BER bits in a digital stream is measured by analyzing the operation of Viterbi, Read-Solomon , LDPC, or BCH decoders. Measuring the voltage level of the radio signal is carried out using a meter integrated with the tuner.
The parameters of television channels are measured according to the frequency plan (table of television channels recorded in the device's memory). Measurement is carried out continuously sequentially over all frequency channels recorded in the device at a certain pace. The measurement results are stored in the memory of the device. The time when the measurement of the corresponding channel was made is also recorded. These results are then available upon request from SNMP over the Ethernet network interface.
Transponder (optical, xWDM)
Optical transponder - a device that provides an interface between terminal access equipment and the WDM line.
Optical signals are received at the inputs of the optical multiplexer , the parameters of which correspond to the standards defined by the G.692 recommendations. This compliance is achieved through the use of a special device in the DWDM equipment - a transponder. This device has a different number of optical inputs and outputs. But if an optical signal can be applied to any transponder input, the parameters of which are determined by rivers. G.957, then its output signals must correspond to the parameters of the rivers. G.692. Moreover, if m optical signals are compressed, then at the transponder output the wavelength of each channel should correspond to only one of them in accordance with the grid of the ITU frequency plan.
The optical interfaces of the DWDM equipment must be compatible with the SDH - STM - 16 equipment. However, according to ITU G.957 recommendations for SDH (SDH) systems, the allowed spectral parameters at the output optical junctions (interfaces) have the following values: spectral line width Δλ≈ ± 0.5 nm (for STM −16), and the central wavelength can be of any value within the range of 1530-1565 nm.
See also
- Transceiver
- Radar
- Aircraft radar transponder