Abstract: An adapter is provided for insertion between a conventional DME airborne interrogator and antenna. The adpater converts conventional interrogations into phase-coded or amplitude coded signals which are received by new Microwave Landing System (MLS) transponders. Each transponder will process interrogations having the correct code and frequency and will respond with precision reply signals. The precision replies are then received by the airborne equipment, converted back to standard reply pulses and processed to provide distance measurement. Also provided is a new transponder for use at MLS sites.