Originally Posted by
chevvron
The articles mention in several places that Russian traffic is 'invisible' to to other aircraft.
Surely there are 'raw' unprocessed primary radars (eg Mount Gabriel) which can detect the blips of ALL traffic even those which do not emit from a transponder or other types of electronic conspicuity.
I've gained the impression that Mt. Gabriel was a secondary surveillance radar only, not primary radar. I seem to recall discussions about the need to "fill in" coverage.