When I was selling my encoding transponder I was surprised at the number of questions asked about Mode 'C'. Yes, the transponder is sold. But here is a brief overview of a Mode 'C' transponder.
All transponders reply to the approach radar interrogation. But what makes it Mode 'C' is that your airplanes altitude is encoded in that reply. The ground based radar operator will actually see on his/her screen, your exact altitude. In order for your transponder to know its altitude, you will need to connect an Altitude Encoder or an Encoding Altimeter (very expensive) into your transponder. Ameri-King builds the AK-350 altitude encoder which is probably the most popular and value priced unit on the market today. Once you have installed the transponder/encoder and connected all the power, antenna, and encoder wires....you will need to have a aviation shop test that the encoding altimeter is calibrated to the proper altitude. Otherwise ATC will tell you that your mode C transponder's altitude is off and needs recalibrated. Good luck guys. Brant Hollensbe Des Moines, Ia bhollen...@mchsi.com
