Posted: Sat Mar 29, 2008 5:38 pm Post subject: Mode C Transponders
A technical question if I may.
How does a transponder obtain altitude information prior to encoding it for an interrogation response?
Is it a separate altimeter in the transponder unit, or does it link into the altimeter? Is it the same static system in use? If it's link to the altimeter, how does changing the subscale affect it? _________________ J.
The old way was to use an encoding altimeter, which basically does what its called. It feeds altitude information to the Transponder and the transponder sends that when interogated. Often these are expensive to repair and an replacement altimeter with no encoder is mucn cheaper.
The subscale on the encoding altimeter makes no difference as what is encoded is atltude above 1013mb, all the time.
The new way is to use an altitude encoder which is basically just an electronic altimeter without a display and that feeds the transponder.
The encoder is usually connected to the Static System with a T-Piece, so the system can then feed both the encoder and the pressure instruments.
The display at the controllers end then calculates the actual level based upon the current QNH.
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum