Can I use an encoder labelled “Mod. 1” in my aircraft?
The Mod. 1 unit is designed to allow Trans-Cal encoders to function with early Narco transponders. This modification removes the decoupling capacitors from the Trans-Cal ICAO altitude outputs. These capacitors normally function to prevent RFI (radio frequency interference) from disrupting the analog circuitry within the Trans-Cal digitizers. When installing a “Mod 1” device in an application without the Narco transponder it will still function; however, care must be taken when installing these units in composite structured aircraft. Conventionally manufactured aircraft present little problem due to the large amount of metal present to absorb stray RFI. Great care should be taken to insure that the Mod. 1 encoder is located away from RF emitting devices and fields. The interconnecting wiring harness must be shielded and properly grounded. Additional shielding around the encoder may be required to prevent stray RFI from disrupting the encoder operation. Mounting any altitude encoder too
