The BID 310, also known as a vocoder, did not encrypt data. Rather, it converted analogue voice (quite poorly) into digital that was then subsequently encrypted by a BID 880. Both units formed part of the UK DSSS system and in fact, the BID 310 was in use with the British Army from the 1970ís until retirement in the early 1990ís
The BID 310 was a complete pain to use. You could change the pitch of person's voice simply by pressing on the top of some of the filter cards. Our sole contributor believes "there were six cards in total with three band pass filters per card. We would often get called out to fix the 310 because someone's voice sounded really weird. Usually the 310 would check out OK on the BITE tests but reseatting the cards would usually clear the problem".