On Thursday, December 14, 2017 at 7:20:02 PM UTC-8, jfitch wrote:

OK, so ADS-B information is transmitted in the blind?

Yep. Completely blind/automatic. That is what the A in ADS-B stands for.

Automatic Dependent Surveillance - Broadcast

Dependent meaning GNSS/GPS.

ADS-B Out broadcasts data messages several times per second completely autonomously, with some pseudorandom time dither to avoid correlated collisions. The mix is a bit complex with ID, status, position and velocity messages broadcast at different rates. Position and velocity are twice per second.

The ADS-B Out side of things make no response to any interrogation and cannot tell if anything is listening. 1090ES Out systems are in practice parts of Mode S transponders and so have a whole slew of other things they do including other automatic broadcasts (like acquisition squitters) and multiple different interrogation types and on high-end transponder even air-air data link for TCAS resolution coordination, etc.. Way more complex than legacy Mode A/C transponders.... and so complex you can see why the expectation back in the early days of ADS-B planning seemed to be that Mode S transponder costs were going to remain high, and why UAT might be a good idea... well no because FPGAs and fast microcontrollers happened and turned transponder hardware into a software problem...