GDL90 Protocol Guide
GDL90 is the standard protocol for transmitting ADS-B traffic and GPS data from receivers like Stratux to Electronic Flight Bag apps. Learn how this Garmin-developed protocol works.
What is GDL90?
GDL90 is a data link protocol originally developed by Garmin for their portable ADS-B receivers. It has become the de facto standard for transmitting ADS-B traffic, GPS position, and AHRS attitude data from portable receivers to aviation apps running on tablets and smartphones.
The protocol uses UDP (User Datagram Protocol) to broadcast data over WiFi, typically on port 4350. This allows multiple devices to receive data simultaneously-you can connect both a pilot's and copilot's tablet to the same Stratux unit.
GDL90 Message Types
| ID | Message | Description |
|---|---|---|
| 0x00 | Heartbeat | Status message sent every second indicating system health and GPS status |
| 0x0A | Ownship Report | Your aircraft's GPS position, altitude, ground speed, and track |
| 0x0B | Ownship Geometric Altitude | GPS-derived altitude for vertical separation information |
| 0x14 | Traffic Report | Other aircraft positions from ADS-B, FLARM, or OGN signals |
| 0x4C | AHRS | Attitude data (pitch, roll, heading) for synthetic vision display |
| 0x65 | Stratux Status | Stratux-specific extension with device status and sensor information |
How GDL90 Works with Stratux
Signal Reception
Stratux SDR radios receive ADS-B (1090 MHz), FLARM (868 MHz), and other signals. The device's GPS module provides your own position. AHRS sensors measure attitude.
Data Processing
The Stratux software decodes raw signals, calculates relative positions, and formats everything into GDL90 messages. Traffic from different sources is unified into a single data stream.
WiFi Broadcast
GDL90 messages are broadcast via UDP on the Stratux WiFi network. Any connected device receives these packets automatically-no pairing or configuration required.
EFB Display
Your EFB app parses GDL90 messages and displays traffic on the moving map. AHRS data enables synthetic vision. The heartbeat message confirms connection status.
Technical Specifications
Alternative Protocols
While GDL90 is the most widely supported protocol, Stratux also outputs data in other formats for specific applications:
NMEA
Standard GPS format, used by some marine and legacy applications
FLARM (Dump1090)
Raw FLARM data stream for advanced integrations
JSON/WebSocket
Web-based interface at 192.168.10.1 for browser access
Frequently Asked Questions
Related Technology Guides
Experience GDL90 with Stratux
All Stratux devices broadcast GDL90 out of the box. Connect your EFB and experience seamless traffic integration.
Disclaimer
Stratux is not certified aviation equipment. It does not replace a transponder or relieve the pilot of traffic awareness responsibilities. Use as supplementary situational awareness only. Dross:Aviation assumes no responsibility or liability for the use of Stratux devices, firmware flashing, or hardware modifications. All DIY guides are provided without warranty-use at your own risk.