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Scott Howard Installation Secrets
Autopilot GPS Gain Select

by Scott Howard, Tech Rep

In the September 1996 issue of The Approach we addressed the subject of GPS tracking sensitivity. In that article we recommended using the "APR" mode in System 40, 50 and 55's for GPS tracking and a special wiring configuration for System 60's and 65's to allow for automatic gain increase when GPS is selected.

The recently introduced Systems Twenty and Thirty incorporate built-in circuitry that allows a special GPS gain enhancement when keyed by the navigation source selector switch. A ground connection is supplied to enable GPS gain.

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This feature has also been incorporated into later model System 40's and 50's as shown below:

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The System's code letter can determine the effectivity of this feature as follows: The code letter can be found at the end of the S/N. System 40, 0129-( ) & 0130-( ), code "C" and above. System 50, 0131-( ) & 0132-( ), code "E" and above. S-TEC recommends the use of this option on all installations of our autopilots that interface with a GPS System.

A GOOD REMINDER
Although S-TEC will modify autopilot roll computers for integration with compatible heading systems if you specify it on the order, the S-TEC fabricated wiring harness will not be altered from the standard version.

This means that the autopilot controller connector on all System Twenty, Thirty, 40 and 50 cables will contain a jumper that disables heading mode engagement. You should always remove the jumper when interfacing with a DG or HSI.

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Another reminder - the heading system cable supplied is wired for an S-TEC DG. This connector will mate to an EDO 52D54/52D154, but the pin configuration is different. When interfacing to this type of DG, the 5-pin plug must be rewired in accordance with the heading interconnect drawing provided. 
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