This invention relates to time division encryption systems and methods.
Voice secrecy can be achieved by digital or analog methods. Methods which are largely digital can produce an extremely high quality encryption. Moreover, the basic encoding is relatively inexpensive. However, these digital methods require a large transmission bandwidth. As a result, if normal telephone lines are to be used, costly equipment is required, and even so good voice recognition is frequently lost in the process.
By contrast, voice secrecy systems which are largely analog can produce a scrambled signal which does not require an appreciable increase in bandwidth compared to the original voice signal. Such systems in the past have however tended to retain some residual speech character and intelligibility which rendered them relatively less secure. In addition, the operation of conventional analog voice scramblers is such that the signal is quite susceptible to degradation when sent over poor transmission lines, both as to amplitude distortion and phase delay distortion.
The present invention teaches a significant improvement of a time division encryption system and method which reduces residual intelligibility to practically zero, eliminating any voice character from the transmitted signal. Furthermore, the encryption disclosed provides an output signal which is less susceptible to distortion by a transmission line.