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Given that the antennae are at surface level and the aircraft are probably between 25,000ft and 40,000ft, I wonder what the ideal maximum range of the receivers would be?

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With a basic RTLSDR and a random small TV antenna (nothing optimized for this use case), from my apartment I've picked up airplanes that were at 40000ft and at a distance of ~ 100 km (62 miles).

Optimizing the antenna and the hardware (and using a lot less cable for the antenna than I have) would probably increase that significantly.

With VHF a handy formula is miles = 1.25sqrt(feet)

So 25000ft gives a range of ~190 miles, 40000ft gives ~240 miles.

Thanks! The target area is approximately 250 miles equidistant from Iceland & Norway, so it's feasible that one of these boats could cover the entire area (under ideal conditions).

ADS-B is not on a VHF frequency.

It is indeed UHF.

I should've put "VHF/UHF" in the original comment as the formula is reasonable for both. They're both Line of Sight and that's really what the approximation is about.

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