The Lilley & Gillie GS820 is an advanced Transmitting Magnetic Compass (TMC) sensor system manufactured by John Lilley & Gillie Ltd. in the United Kingdom. Designed to digitize traditional magnetic compass readings, the GS820 attaches to the base of a Class A magnetic compass bowl (such as the Lilley & Gillie SR4) to convert physical compass card orientation into high-precision NMEA 0183 digital heading data.

By delivering digital heading signals directly to vessel bridge equipment—including radar, ECDIS, autopilots, off-course alarms, and digital repeaters—the GS820 fulfills IMO SOLAS requirements for Transmitting Heading Devices (THD). Featuring solid-state magnetic detection, electronic deviation correction, and rugged marine construction, it provides continuous digital heading transmission without interfering with the mechanical movement of the primary magnetic compass.

Key Features:
• Converts Magnetic Compass to Digital Heading: Transmits real-time digital heading from a mechanical magnetic compass to vessel electronic networks.
• NMEA 0183 Serial Output: Generates standard IEC 61162-1 serial data ($HCHDG, $HCHDT) for universal bridge system compatibility.
• Non-Interfering Sensing Coil: Mounts externally underneath the compass bowl without affecting magnetic card balance or fluid stability.
• Integrated Deviation Correction: Features electronic calibration to compensate for residual vessel deviation and deliver accurate heading outputs.
• High Resolution & Responsiveness: Provides fine angular resolution down to 0.1° for precise autopilot steering and responsive heading displays.
• SOLAS Transmitting Heading Device (THD): Complies with international IMO performance standards for electronic magnetic heading transmission systems.