Newps wrote:

Irrelavant. The radar computer has software that will not show any
target within the user specified distance from the radar antenna. We
set ours to 1 mile. There are also altitude filters that can be set.
There is no good reason to ever turn your transponder off or to STBY
unless ATC asks you to or you somehow know it's not working properly.

There's still another problem called FRUIT (False Replies Unsynchronised
in Time). The radar bean has a width of about 3 degrees. All the
transponders in this small area respond with their code as soon as the
radar beam hits them. A major installation can handle up to ten codes
simultaneously. But if on a nice Sunday several hundred VFR air planes
are about the situation has arisen where the targets could no longer be
properly separated, with the result that the important echoes of
commercial traffic disappeared in the maze.

The controller can erase the VFR echoes, but when the radar con not read
them anymore the legibility of the remaining echoes is not improved.
Actually, this is one of the reasons why mode S is introduced.

Stefan