Just to put the above post on power into perspective then have a read of this slide pack looking at
very low power ADS-B for drones at 0.1W and 1W:
https://www.icao.int/MID/Documents/2019 ... 090MHz.pdfI guess that EUROCONTROL have been doing their own modelling in light of some of the wild claims about 1090Mhz frequency when using lower power devices (those claims are untrue from my own viewpoint, and it is the 70W, 125W and 400W-500W transponders that cause the issues).
They predict a 98.5% probability of detection of a 0.1W ADS-B signal over a 5 second period (in an environment of 3 other small drones operating within a km of each other near either Charles De Gaulle Airport or Frankfurt Airport with lots of transmissions on 1090Mhz) - that range was 0.8nm for guaranteed detection in the worst case scenario. For the 1W ADS-B signal in a similar environment that guaranteed detection was 2.3nm. The snag being that if there many drones all equipped with 1W then the modelling predicted a reduction of all other ADS-B signals by 41%, whereas the 0.1W saw a very small reduction of less than 8%.
So, on the basis of that, I would offer that
very low power ADS-B for small drones (2-25kg in mass) using 0.1W would be ok if you could guarantee getting a warning by roughly 1 mile from it, and a 50% likelihood of detection at 3-4nm (interpolating from the graphs).
Obviously, for 20W then SkyEcho would significantly improve on those ranges - 70W shows about 21nm for 98.5% and 1W is 2.3nm, so if we take a broadly linear relation then 20W would be around 6nm for guaranteed reception between aircraft when the 1090Mhz frequency is at peak use. Again, I’ll accept that for what it is if any aircraft is going to detect mine at 6nm.
But [health warning] there is a bit of interpretation in my final conclusion.