Secure phones - STU3

For those of you interested in STU-III's, there was an article several years ago in "Speech Technology" Magazine (now out of business), that explained quite a bit about the Motorola Sectel 1500. The 1500 is a Type I phone (OK for classified conversations). The crypto used wasn't discussed, but there were pictures and an explanation of the speech coding used and well as the feature set. That particular phone would speech code using LPC-10e @ 2400 bps or MRELP (Modified Residual Excitation Linear Prediction) at 9600 bps. Using the 2400 bps speech coder, you could interleave data (either syncronous or async) and speech. If anyone is interested, I can look up the citation. Eric Blossom