Found an article on Don Hings WS27, WS58, seems it might have had something to do with the modulation(not that I understand what that is) but he mentions it was what made the sets possible in the first place, perhaps that is why it required a unique type power source. Battery consumption was greatly reduced, as well as the weight of the equipment, ranges seem to be greater than similar USA and British equipment.
Geoff
http://www.hyperstealth.com/DonHings...evelopment.PDF