Squitter refers to random pulses, pulse-pairs and other non-solicited messages used in various aviation radio systems' signal maintenance. Squitter pulses were originally, and are still, used in the DME/

TACAN A tactical air navigation system, commonly referred to by the acronym TACAN, is a navigation system used by military aircraft. It provides the user with bearing and distance (slant-range or hypotenuse) to a ground or ship-borne station. It is a mor ...

air navigation systems. Squitter pulses, because of their randomness and identical appearance to standard reply pulse-pairs, appear the same as unsolicited/unsynchronised replies to other interrogating aircraft. Squitter was first used in the original

IFF In logic and related fields such as mathematics and philosophy, "if and only if" (shortened as "iff") is a biconditional logical connective between statements, where either both statements are true or both are false. The connective is bicon ...

systems. These used a superregenerative receiver which greatly amplified input signals using

positive feedback Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the ...

. If the

gain Gain or GAIN may refer to: Science and technology * Gain (electronics), an electronics and signal processing term * Antenna gain * Gain (laser), the amplification involved in laser emission * Gain (projection screens) * Information gain in de ...

was set too high, random radio noise like

static Static may refer to: Places *Static Nunatak, a nunatak in Antarctica United States * Static, Kentucky and Tennessee *Static Peak, a mountain in Wyoming **Static Peak Divide, a mountain pass near the peak Science and technology Physics *Static el ...

would enter the amplifier and cause it to send out a signal, creating random signals. An

automatic gain control Automatic gain control (AGC) is a closed-loop feedback regulating circuit in an amplifier or chain of amplifiers, the purpose of which is to maintain a suitable signal amplitude at its output, despite variation of the signal amplitude at the inpu ...

system on subsequent models cured this problem. Primarily, squitter is used to maintain a regular signal from the ground beacon. In the TACAN system, signal strength variation due to rotation of the transmitting beam (amplitude modulation) determines the course bearing function. This function would be lost without a constant 2700-4800 pulse-pairs per second,

carrier Carrier may refer to: Entertainment * ''Carrier'' (album), a 2013 album by The Dodos * ''Carrier'' (board game), a South Pacific World War II board game * ''Carrier'' (TV series), a ten-part documentary miniseries that aired on PBS in April 20 ...

-like signal in cases of low or no interrogating aircraft. In the Mode S

secondary surveillance radar Secondary surveillance radar (SSR)''Secondary Surveillance Radar'', Stevens M.C. Artech House, is a radar system used in air traffic control (ATC), that unlike primary radar systems that measure the bearing and distance of targets using the de ...

system, the term is used to describe messages that are unsolicited downlink transmissions from an

automatic dependent surveillance-broadcast Automatic may refer to: Music Bands * Automatic (band), Australian rock band * Automatic (American band), American rock band * The Automatic, a Welsh alternative rock band Albums * ''Automatic'' (Jack Bruce album), a 1983 electronic rock ...

(ADS-B) Mode S transponder system. Mode S

transponders In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend of ''transmitter'' and ''responder''. In air navigation or radio frequency identification, a flight trans ...

transmit acquisition squitter (unsolicited downlink transmissions) to permit passive acquisition by interrogators with broad antenna beams, where active acquisition may be hindered by all-call synchronous garble. Examples of such interrogators are an

airborne collision avoidance system An airborne collision avoidance system (ACAS, usually pronounced as ''ay-kas'') operates independently of ground-based equipment and air traffic control in warning pilots of the presence of other aircraft that may present a threat of collision. ...

and an airport surface system.

External links

SSR
a
AIS-P/TailLight
Air traffic control Radar Avionics {{comm-stub de:Sekundärradar fr:Radar secondaire no:Sekundærradar fi:Toisiotutka