Hi Allen & all

This is dredged up from a distant memory, but it worked by splitting
incoming bees and out going bees.

The entrance was three parallel sheets of thin ply with  bee spaces between.
The upper space was "incoming" and was fitted with a dozen or so porter
escapes to allow bees in, but not out.

The topmost and lowest sheet of ply were 50 mm shorter than the middle one
and the outgoing slot was painted with matt black "blackboard" paint.

Entry to the outgoing slot from inside the hive was through a piece of round
hole pollen stripper grid.

It worked as all bees arriving back from foraging were descending and landed
on the projecting "shelf"

Any orienting bee on its first flight would rise about 150 mm before taking
it's first "fix" and so would return to the top slot.
The projection hid the bottom slot from sight.

Regards From:- Dave Cushman, G8MZY
Beekeeping and Bee Breeding, http://website.lineone.net/~dave.cushman
IBList Archives, http://website.lineone.net/~d.cushman