Types of Aircraft Transponders and their Use in Aviation

What is Transponder?


There are two types of equipment used in telecommunications, one of which is a transponder. An autonomous transceiver in an aircraft that responds to an interrogated receive signal for radio frequency identification (RFID) or air navigation by sending out a coded identifying signal is known as a flying transponder. Without altering the received signal or signals, a satellite transponder in a communications satellite usually receives signals via the uplink frequency range of a satellite earth station, amplifies them, and retransmits them to receivers on Earth at a distinct set of downlink frequencies.

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An aircraft is equipped with an electronic device known as a transponder, which makes it easier for air traffic controllers to recognize it on their radar screen. This part of the secondary surveillance radar system is airborne, thus every pilot is familiar with it. An aircraft cannot display secondary data on the air traffic control radar beacon system (ATCRBS) without a transponder. It automatically detects radio signals from ground-based interrogators and only transmits a certain reply pulse or group in response to interrogators detected in the transponder’s chosen mode.

How does a Transponder Work?

A transponder functions mostly like an electrical circuit with a transmitter and receiver. Transponders are typically seen in satellites. After receiving signals from ground stations, satellite transponders retransmit or broadcast those signals to earth stations. Additionally, transponders will perform tasks like frequency conversion, noise reduction, and signal amplification.

For instance, one ground station can uplink the channels to transponders aboard satellites to enable DTH services using transponders. The signals are transmitted to Earth by these transponders.

Different types of Transponder

Because each channel in a communications satellite is an independent transceiver or repeater, they are referred to as transponders. Multiple video and audio channels can go through a single transponder on a single broadband carrier thanks to digital video data compression and multiplexing. A transponder is a component used in fiber optic communications that transmits and receives optical signals from an optical fiber. Transponders are generally distinguished by the maximum signal length and data rate that they can handle.

A different kind of transponder is used in air traffic control secondary surveillance radar (beacon radar) systems for general and commercial aircraft as well as identification friend or foe systems in military aviation. Large, all-metal aircraft are the ideal fit for primary radars, which perform less well on smaller, composite aircraft. Regardless of the size of the passenger ship, Automatic Identification Systems (AIS) must be installed on ships of 300 gross tons (GT) or more for international voyages, according to the International Convention for the Safety of Life at Sea (SOLAS) of the International Maritime Organization (IMO). The transponder in many contemporary automobiles is concealed inside the plastic key head.

Types of Aircraft Transponders

  • Transponder S: Provide the air traffic control tower with a transponder code and altitude information. Gather information from similar transponders and forward it to them.
  • Transponder A: ATC should receive the transponder codes back.
  • Transponder C: ATC should receive transponder codes and altitude information.

Passive Transponders of Aircraft Transponders

Passive integrated transponders, or PIT tags, are tracking devices that operate without the need for power. Rather, they have an internal microchip that activates upon contact with a specific antenna. The characteristics of the tag and the instant it passed by the antenna are recorded by the computer to which the antenna is attached. An example of this tag that you may be familiar with is the “E-ZPass” that your parents use when driving. An EZ-Pass doesn’t require power to operate. An enormous antenna on the toll gates connects with the tag to identify the vehicle and record the time it takes to pass the barrier.

Active Transponders of Aircraft Transponders

The active transponder, commonly referred to as an active tag, is an RFID device that has an embedded battery for longer battery life. The greater power results in a longer reading distance when compared to a passive tag. Because they broadcast their own signal continuously, active transponders are particularly useful in situations where tracking or monitoring must be done continuously. Applications for which they are commonly used include navigation, identification, and location systems for both private and commercial aircraft.

In order to aid air traffic controllers in recognizing the aircraft and preserving distance between them, the transponder provides an altitude message (Mode C) or a transponder code (commonly referred to as a “squawk code”; Mode A). Another option dubbed option S (Mode Selection) was developed to help prevent excessive transponder interrogation and to enable automatic collision avoidance because there are many radars in crowded areas.

Transponders capable of operating in modes A and C can also function in mode S. Mode S is necessary in regulated airspace in several countries. Furthermore, a number of countries have mandated—or are in the process of mandating—that all aircraft, even those operating in uncontrolled airspace, be equipped with Mode S. However, general aviation is against these endeavors because to the cost, size, negligible benefit to users of uncontrolled airspace, and power requirements on long-haul flights in the case of gliders and balloons.

Key Features of Aircraft Transponders

  • A passive device does not require an external power source, unless it is an active transponder.
  • Examples of fixed information content that may be provided are ramp values, speed limit values, interval lengths, mileposts, etc.
  • A variable code transponder can provide real-time information such as through, in and out of the station, lane number, etc.
  • Low maintenance needs and a long service life can cut down on maintenance expenses.
  • Large-scale information transmission contributes to the realization of the system’s “fault a safety” potential since it is not limited by the physical limitations of the road.
  • There is no frequency band restriction while using flexible frequency.
  • If the electromagnetic field is stable, you can achieve a very high-quality transmission effect.
  • One might use a single investment to fund a variety of services.

Aircraft Transponder Settings

There are several parameters on each transponder, and these can vary significantly based on the manufacturer and installation.  The STANDBY and ON settings are both fairly obvious. A unique mode can be triggered by setting the transponder to the ALT setting.  This tells the transponder to send out a signal containing the four-digit code the pilot has selected, together with the airplane’s altitude data.  This is referred to as Mode C, and ATC finds it particularly beneficial.  Along with the transponder signal from the aircraft, radar displays in Mode C also show the aircraft’s height above sea level. It is still really astounding, even though the resolution is only accurate to 200 feet.

Aircraft flying in heavily controlled airspace need ATC to provide extra information.  Class B (Bravo) airspace encircles the busiest and largest airports, such as those in Atlanta, Los Angeles, and Chicago, among others.  When an aircraft is within 30 nautical miles of these airports, it is required to squawk in Mode C.  It is called the “mode C veil.”  All planes with transponders that are unable to squawk mode C should avoid flying over class B airports because they are just too close.

How does a Aircraft Transponder Work?

Transponder operations are standardized by ICAO Annex 10 Volume IV. Initially, the ground interrogator (or, in the case of TCAS, the aerial interrogator) broadcasts a 1030MHz interrogation sequence to every aircraft in the vicinity, either continuously for Mode A/C or selectively for Mode S. As soon as the airplane transponder receives the signal, it rapidly answers on 1090MHz. After processing, the data is sent to the display of the controller, where it is utilized by safety nets and tools, after the ground station receives the return signal.

How can one use Squawk Codes?

Whether it comes from the air or the ground, the first clearance a flight gets from air traffic control usually has a squawk code. If the flight is VFR, the pilot will either set a squawk of 1200 in the US or 7000 in much of the rest of the world.

When the controller receives a squawk code unique to that aircraft, the flight number or registration of the aircraft will show up on the screen.

Air traffic control “primary radars” show the aircraft’s bearing and separation from the radar. Secondary Surveillance Radar (SSR) will provide controllers more information gleaned from the squawk code.

Future Trend of Aircraft Transponders

The market for aviation transponders is predicted to increase significantly over the next several years, with a strong current outlook. This can be ascribed to a number of things, including the growth in air traffic around the globe, the increased need for effective air traffic control systems, and the introduction of new laws pertaining to aircraft safety and surveillance.

Furthermore, technological developments have resulted in the creation of sophisticated transponders with improved features, such as ADS-B (Automatic Dependent Surveillance-Broadcast) and Mode S. In the end, these technologies improve the efficiency and safety of the aviation sector by enabling more precise and dependable data transfer. The need for aviation transponders is being further fueled by the growing emphasis on updating airports and airspace infrastructure as well as the expanding use of unmanned aerial vehicles (UAVs) in both military and commercial applications.