GARMIN GAD-29 ?

[DCarlton]

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]

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]

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]

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]

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.