encoding altimeter

The normal altimeter but with the additional capability for sending digitalized output to the transponder for transmission to ATC (air traffic control). The encoding altimeter, in conjunction with a transponder, transmits the aircraft altitude in hundreds of ft to the radar of the air traffic control radar beacon system.

An encoded altimeter transmits the aircraft altitude to the radar of the attached radar beacon system. It essentially consists of an encoding disc which rotates as per altimeter reading. This rotation of the disc is sensed by photo cells. These digital signals are amplified and transmitted. The transponder receives these as pressure altitude. The computer converts these signals on the basis of local altimeter setting. This ensures that there is uniform information in respect of all aircraft in the region.