I recently bought a software defined radio to experiment with ads-b on the 978 and 1090mhz bands. It's pretty cool to be able to independently track transponders of aircraft without an internet connection necessary. I know that at some point the holy grail of UAS is going to be the so-called sense and avoid systems that rely on various implementations of ads-b in and out. The main stumbling block right now is cost of the equipment and the size/power requirements. I know there are a few examples but they are still too large to fit on something the size of a phantom. So why not have a ground based transmitter instead? The information being broadcast is the basic position, speed, altitude, and heading. All of that is currently available in telemetry being downlinked from our drones. The DJI sdk allows you to tap into that data for 3rd party apps. Conceivably, something could be put together that would take that data in real time and broadcast it back out from the ground. With very little effort (and expense <$30), I'm pulling transponder info from over 50 miles away. Obviously transmitting from the ground would have range problems, but even if it could do 10 miles, it would be a plus. Transmitters are also more costly than receivers alone, but that's not really my point. The other shortcoming would obviously be that such a setup would stop working in a control link failure scenario, but hopefully the return to home would get you back in range. In general, this could take care of the major obstacle of size, weight, and power of the equipment since it would not need to be actually flying. What else am I missing? Why isn't this a thing?