Simrad Autopilot AP26 - Manual (Page 15)

System Description
20221586B
13
floating ring core in a fluxgate coil and transformed to a digital
signal read by the autopilot steering computer.
RFC35 can operate as a low cost back-up compass for the AP26
and AP27 autopilots.
NMEA compass (optional)
A well performing compass that outputs NMEA 0183 HDT or
HDG messages at 10 Hz can be connected directly to the AC20
or AC40 autopilot computer.
It is absolutely necessary for the autopilot that the heading rate is
minimum 10 Hz.
Simrad RGC10 and RGC50 gyrocompasses
The optional GI51 unit is needed to interface these two
gyrocompass models. Ask your Simrad dealer for information.