Of course Pongo. But I meant that in actual WW2 the device was handy although, AFAIK, it was pretty rare even as tank equipment. The advantage of it lies in a belief (or fact) that the enemy does not have similar equipment.
BTW, to those who have not thought about it, the radar has the same problem of passive detection. If you switch on your radar you can be detected by longer ranges that you can actually see by yourself while using the radar.
-C+