Secure Digital Voice Communications In World War II

mercury7 writes: "Saw this one on Memepool. A very interesting paper from the U.S. National Security Agency site on the first digital encyrpted voice communication system. It is incredible how hard it was to manipulate data before the existence of computers."

Comments

incredible

[burris]

The system required that the key be used in twenty millisecond segments. Therefore, it was necessary for each record to be kept in synchronism within a few milliseconds for fairly long periods of time (one hour or so). This was accomplished by the use of very precisely driven turntables. The turntables themselves were remarkable machines. Each was driven by a large (about thirty-pound) synchronous electric motor with hundreds of poles. The motor was kept in constant operation, and the power for it was derived directly from dividing down the terminal's frequency standard. The frequency standard was a 100 kHz crystal oscillator. The accuracy of the standard had to be maintained within about one part in ten million so that the system would stay in synchronism for long periods of time. The system frequency standard could be corrected by comparing it to an available national frequency standard (which was WWV in the U.S.).

For reference, the clock in a high performance modern digital audio device is only accurate to within about 1-10ppm. A cheap consumer device like a CD player or walkman type DAT deck will only have about 50-100ppm accuracy. This is 0.1ppm, in 1943, for a freakin' record player. Absolutely amazing.

Burris