Here's a line from the KTB of U-466 from June-August 1943:
Dived for detection on 134 cm wave, 2 second impulses, recurring. Skilled operator. [Used radar] sparingly.
http://www.uboatarchive.net/KTB466-3.htm
The allied started switching their radars off now and then while approaching the U-boat to lessen the possibility of getting detected by RWR. Maybe this could be randomized somehow in order to have the crewmen sometimes miss the approaching airplane/destroyer altogether?