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configurable GPS, take 2

Posted: Wed Oct 21, 2020 10:27 pm
by rv7charlie

I have a ublox GPS puck as GPS1. I originally configured it with a stripped down 'sentence' set, because I could only run it at 9600 baud with one update per second on another system. Sentences are:
GXGGA, GXGSA, GXGSV, and GXRMC. I now have it installed as GPS1 on my Horizon HX, still at 9600 baud. The HX drives a Trio EZPilot with altitude hold module. The autopilot is a bit 'lazy' about holding a course, and not great at turning on course when intercepting. I'm reconfiguring for 115200 baud and higher update rate.

My question: Are there any GPS sentences I should add back to it's configuration, that would have any effect on (improve) the autopilot's turn anticipation, tracking, etc? Or do I already have all needed sentences, and therefore need to look only at the autopilot configuration?

Many thanks,


Re: configurable GPS, take 2

Posted: Thu Oct 22, 2020 9:51 pm
by GRT_Jeff
The EFIS mainly wants GPRMC or GNRMC. It will also use GPGGA or GNGGA for altitude and a few others for status but those don't help the autopilot. Sentences where X is not "P" are new sentences for multi-system satellite tracking that aren't part of the original standard and may not be supported by the autopilot. The autopilot wants GPRMC from the GPS. The EFIS will convert GN sentences to GP sentences to make them compatible with more autopilots.

The EFIS updates its own position information 15 times per second using AHRS data, so faster GPS updates usually don't have much of an effect on internal modes and plans.

Even if the GPS update rate is higher, the autopilot output of the EFIS may be limited to once per second.

Make sure the Autopilot Serial Output in the EFIS General Setup is set to "Normal" since your autopilot has its own GPS tracking and intercept capability.

Re: configurable GPS, take 2

Posted: Fri Oct 23, 2020 4:31 pm
by rv7charlie
Will do. Thanks for the great support! I'm really enjoying this 'old technology' EFIS. :-)