GDL 82 aviation surveillance device

The Garmin GDL 82 is a remote-mounted UAT transmitter for ADS-B Out, a transponder-interfaced surveillance unit that lets an aircraft broadcast its position, altitude and identity on the 978 MHz Universal Access Transceiver datalink. It is installed in-line between an existing Mode A/C transponder and the L-band antenna, so no second antenna is needed for the transmitter.

The unit contains 978 MHz and 1030 MHz transmitters and a 1090 MHz receiver. It sends ownship ADS-B Out data over the UAT link through the transponder's own L-band antenna, and uses the in-line connection to follow the transponder: through the 1030 MHz interrogations it obtains the squawk (Mode 3/A) code, the IDENT state and the pressure altitude. Installed as described in the Mooney M20 series STC manual, it satisfies the ADS-B Out equipage requirement of 14 CFR 91.225 and 91.227, following the guidance of AC 20-165B.

Position data come from a GPS/SBAS source. The GDL 82 w/ GPS version has an internal GPS receiver and a coaxial connection for a GPS antenna; the base version takes position over its RS-232 input from an approved navigator. The approved sources in that manual are the GTN 6XX/7XX series, GNS 4XXW/5XXW series, GPS 175, GNC 355 and GNS 480 navigators, or an existing approved GPS antenna installation for the internal receiver.

Physically, the unit measures 3.39 in wide, 1.48 in high and 7.99 in long. With connectors it weighs 0.99 lbs, or 1.22 lbs for the GDL 82 w/ GPS. It runs from 14 VDC or 28 VDC aircraft power. The base unit draws 0.35 A typical and 0.4 A maximum at 14 VDC, and 0.2 A typical and 0.25 A maximum at 28 VDC; the GPS version draws 0.45 A typical and 0.5 A maximum at 14 VDC, and 0.25 A typical and 0.3 A maximum at 28 VDC.

The interfaces are aircraft power and ground, the transponder coaxial connection, the L-band coaxial connection, the GPS coaxial connection (internal GPS only), one RS-232 input and output for an external GPS source, a USB port for configuration and software loading from a PC, one discrete output for an optional failure annunciator and two discrete inputs for an optional anonymous mode switch and an optional squat switch. The STC manual covers installation on the equipment shelf in the aft fuselage or under the instrument panel of Mooney M20 aircraft.

The GDL 82 is aimed at general aviation and light aircraft that need to meet ADS-B Out rules while keeping their existing transponder. Its footprint, low current draw and simple wiring also suit installation planning for other light manned aircraft platforms, subject to the approval basis of each installation.