STX 165 :: What is the Strobe Line? Jul 23, 2014 | What is the Strobe Line? 1 Comment admin on July 23, 2014 at 6:47 pm Older transponders”Strobed” encoders whenever they wanted an altitude update. This is not required in newer transponder systems. When the STX 165 altitude output is being used by another system that does not require a strobe, a ground on the STX 165 Strobe line is usually required.