Abstract: A secure communication system comprising:a first cyclical pseudo-random noise generator comprising determinable vable starting point means and an output;transmitting means for transmitting said pseudo-random noise generator output;receiving means for receiving said transmitting means transmissions, said receiving means having an output;recycling storage means for storing said receiving means output;a second cyclical pseudo-random noise generator identical to said first pseudo-random noise generator having an output and a reset input, said receiving means output connected to said reset input;a correlator having a first input connected to said storage means and a second input connected to said second pseudo-random noise generator output and an output from said correlator; andtiming means connected to said receiving means output and said correlator output for measuring time elapsed between any output of said receiver and said correlator.

Abstract: Longitudinal shocks and longitudinal emotional disturbances are reduced between members attached to opposite ends of a vibration isolation module. An elongate, essentially cylindrically shaped cord extends the length of the module and is fabricated from a compliant and dissipative material. At least one cord-like essentially nonextensible member is wound about the core in a helical fashion with at least one symmetrically located pitch reversal, and with attachment to the core at least at the ends and pitch reversal points. Longitudinal shocks and motional disturbances are translated by the essentially nonextensible cord-like member into torsional shear strains in the compliant core. The dissipative characteristics of the core material coupled with the nonlinear relationship between longitudinal and torsional strain produce a tensile shock absorber with both damping and a spring constant that increases with longitudinal strain.

Abstract: 1. An encoded echo-ranging signal generator comprising in combination;A digital shift register having a plurality of binary encoded stages,A shift pulse generator coupled to said digital shift register for the tiy shifting thereof,An anti-coincidence circuit having a pair of inputs and an output with one of said inputs being connected to a predetermined stage of said digital shaft register and the other input thereof coupled to the output of said digital shift register and with the output thereof connected to the input of said digital shaft register, to randomly recirculate through said register the binary contents of said encoded stages,An echo-ranging system coupled to the output of said digital shift register,And a digital message encoder coupled to said digital shift register for the respective binary bit encoding of each stage thereof.