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PUBLISHED: 17:31 01 December 2008 | UPDATED: 13:56 10 October 2012

TT21 Mode S transponder is world’s smallest and lightest

TRIG Avionics has introduced a new lightweight Mode S transponder. The TT21 transponder system meets all the Mode S transponder requirements but weighs less than 500 grams. With an ultra-compact front panel controller and a small transponder block the new TT21 will squeeze into any aircraft. Ideal for light sport and microlight aircraft, as well as conventional light aircraft where there is not much panel space, the TT21 low power design means that it can also run on batteries for gliders and balloons.The TT21 is a two part system – the front panel controller features an LCD display and conventional controls, and incorporates an altitude encoder, whilst the remote transponder box contains the power supply and the receiver/transmitter. The rear box is not much larger than a pack of cards, and can be mounted anywhere convenient in the aircraft. Despite the small size the TT21 nominal power output for reply pulses is 130 Watts, and it even supports ADS-B out using 1090MHz extended squitters, which means that it offers a path to future ADS-B based surveillance.The TT21 will initially be certified in Europe and the USA. The TT21 will be available in February 2009, and is expected to retail for around £1,295 / €1,620 (plus taxes).More information is available at

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