The Garmin GTX-330D is a solid-state Diversity Mode S Transponder that operates on radar frequencies, receiving ground radar or TCAS interrogations at 1030 MHz and transmitting a coded response of pulses to ground-based radar on a frequency of 1090 MHz. The GTX-330D is equipped with IDENT capability that activates the Special Position Identification pulse for 18 seconds. The GTX-330D replies to ATCRBS Mode A, Mode C and Mode S All-Call interrogation. Mode A replies with any one of 4,096 codes. Mode C replies with framing pulses and encoded altitude. Mode S replies with selective identification codes, aircraft type, aircraft id, Comm-A and Comm-B.

The GTX-330D has variations available with either a black or gray bezel as well as variations available with Extended Squitter (ES) for ADS-B out capability. The GTX-330D operates at a maximum altitude of +55,000 feet and a temperature range of -45°C to +70°C. The GTX-330D is 1.65 inches high, 11.25 inches deep, 6.25 inches wide and weighs 4.20 pounds.