What’s the difference between ADS-B and transponder?
Mode S transponders respond to interrogation and rely on multilateration to estimate aircraft position. ADS-B Out broadcasts precise GPS position continuously, allowing ATC and nearby aircraft with ADS-B In to see traffic directly. However, the main difference lies in the amount of information transmitted. The message from a Mode C/S transponder is much less detailed than that of ADS-B. In the message from Mode C/S transponders, precise location is missing although both types will give a standard pressure altitude for the other aircraft.
What are the two types of ADS-B?
ADS–B is a performance–based surveillance technology that is more precise than radar and consists of two different services: ADS–B Out and ADS–B In. ADS-B Out works by broadcasting information about an aircraft’s GPS location, altitude, ground speed and other data to ground stations and other aircraft, once per second. ADS-B ground stations are smaller and more adaptable than radar towers and can be placed in locations not possible with radar. With ground stations in place throughout the country, even in hard to reach areas, ADS-B provides better visibility regardless of the terrain or other obstacles.