Isnt this simple math?
you get a 3 db loss every 100 meters?
and you need to go 1k meters?
But you need to be above 20db for an snr?
3 x 10 = 30 +20 = 50
So you would need 50 for an snr in order to go 1k meters if you have a 3db loss every 100 meters.
They only care about the snr though? not the Tx power? Thats weird, its a one way system?
Hope that helps.