I've got two nice source of testing for my RD's, a Whistler 1793SE and a Cobra 9400... the county PD, which uses mainly constant-on Ka and a local college campus's PD, which uses constant-on Ka too, though a different type of gun. I've yet to work up the courage to ask what kind either are, but from looks and behavior they are definitely different.
One interesting phenomenon I've noticed is that the Cobra doesn't always pick up the campus PD's Ka guns. With the county PD, both my whistler and my cobra have "similar" detection range, usually the Cobra is 25% or so weaker though and strength never rises above 1/5.
However, with the campus PD, more often than not my cobra is dead silent when driving past their cruisers, sometimes only giving a momentary alert when I'm just a few feet away from the cruiser. My whistler, however, is just as perky with the campus PD signals as with any other Ka band signal, giving me alerts before I can even see the police car.
Has anyone else noticed this kind of "selective deafness"?