Why does the 1090 ES use the same frequency for both uplink and downlink? The 1090 ES is the transponder system used in ADS-B.
Why does the 1090 ES use the same frequency (1090MHz) for uplink as well as downlink? 1090 ES is an extension of Mode S. The Mode S used 1030MHz for uplink and 1090MHz for downlink. Why did the 1090 ES change that? Having two frequency channels would be better (More space less noise due to message collisions) for communication right?
It's a broadcast protocol - devices spontaneously announce themselves for listeners to hear. There are no interrogations to put on a different channel.