I have seen a few posts where a range map of the adsb receiver was shown, can somebody tell me how to generate this?
Please be more specific. Theoretical range outlines can be generated like this: https://discussions.flightaware.com/t/what-is-the-maximum-range-i-can-get/17248 Placing it in the html directory of whatever dump1090 webinterface you are using should make it appear on your local web interface: https://github.com/wiedehopf/tar1090#heywhatsthatcom-range-outline
Well that's the possible range related to the terrain. Your effective range depends on where exactly the antenna is and the receiving gear. Anyhow air traffic over Europe is MUCH LESS than usual at the moment.
