The non‐synchronous techniques: Collision avoidance

Abstract

SECANT is an acronym that stands for the SEparation and Control of Aircraft using Non‐synchronous Techniques. It is a cooperative transponding system which operates at L‐band, and performs the collision avoidance function by transmitting probes and receiving replies with a 1‐microsecond pulse, at 1,000 pulses/sec, on 24 different frequencies. Various discriminants are used to eliminate the undesired signals or “fruit”: different frequencies are allocated as a function of altitude of the flight of the aircraft; the fields above and below the aircraft are probed separately; analogue thresholds are established, based on the range required for the collision avoidance function, which discriminate against signals coming from aircraft too far away to be involved.

Citation

(1972), "The non‐synchronous techniques: Collision avoidance", Aircraft Engineering and Aerospace Technology, Vol. 44 No. 3, pp. 16-19. https://doi.org/10.1108/eb034879