DCarlton Posted August 31, 2022 Report Posted August 31, 2022 The GAD-29 can provide analog heading and course error outputs for third party analog autopilots. Does anyone happen to know the specs for those various analog outputs? Guessing its + / - volts per degrees of deviation left or right. It also has an AC reference signal input. Curious if that's most often 400 hz. Appreciate anyone's time that happens to know. I doubt the Garmin docs provide those details. Thanks!
N201MKTurbo Posted September 1, 2022 Report Posted September 1, 2022 The GAD29 autopilot output simulates the differential transformer found in directional gyros. The autopilot supplies an AC reference signal and the transformer sends a signals that Varies in phase and amplitude depending on the direction and distance from the heading bug. The GAD 29 receives the reference signal and decodes it with an A/D converter and uses software to generate the AC error signal using a D/A converter. This signal is coupled back to the autopilot through a small transformer.
DCarlton Posted September 1, 2022 Author Report Posted September 1, 2022 14 hours ago, N201MKTurbo said: The GAD29 autopilot output simulates the differential transformer found in directional gyros. The autopilot supplies an AC reference signal and the transformer sends a signals that Varies in phase and amplitude depending on the direction and distance from the heading bug. The GAD 29 receives the reference signal and decodes it with an A/D converter and uses software to generate the AC error signal using a D/A converter. This signal is coupled back to the autopilot through a small transformer. Your description resonates with what I was hoping. Any idea what AC error signal looks like? Volts per degrees of deviation off the line? With my current DG, I believe 30 degrees off the line gets you around 4.5 v. Tracking the course gets you 0 v. Any idea what the little transformer does between the D/A converter and autopilot. Appreciate your time and knowledge! Thanks.
N201MKTurbo Posted September 1, 2022 Report Posted September 1, 2022 7 minutes ago, DCarlton said: Your description resonates with what I was hoping. Any idea what AC error signal looks like? Volts per degrees of deviation off the line? With my current DG, I believe 30 degrees off the line gets you around 4.5 v. Tracking the course gets you 0 v. Any idea what the little transformer does between the D/A converter and autopilot. Appreciate your time and knowledge! Thanks. There is no DC voltage error from the DG. The AC signal must be demodulated to get a DC error signal. This method has been in use for decades because it was easy to realize with simple analog parts and it was very reliable. I believe the error signal is a +- phase difference. The transformers convert the ground referenced signal from the GAD29 into a floating AC signal.
DCarlton Posted September 1, 2022 Author Report Posted September 1, 2022 3 minutes ago, N201MKTurbo said: There is no DC voltage error from the DG. The AC signal must be demodulated to get a DC error signal. This method has been in use for decades because it was easy to realize with simple analog parts and it was very reliable. I believe the error signal is a +- phase difference. The transformers convert the ground referenced signal from the GAD29 into a floating AC signal. I may have measured those voltages at test points on my Brittain DG adapter. Will chew on this. Thanks.
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