Abstract: 1.

Abstract: A secure sonar communication system for transmitting and receiving intellnce signals within an aqueous medium comprising in combination means for generating an electrical pseudo random noise signal within a predetermined bandwidth, means connected to said pseudo random noise generating means for selectively driving same at one of a plurality of predetermined frequencies, keying oscillator means adapted to selectively produce an output of one of a plurality of predetermined frequency signals, a balanced modulator means coupled to said pseudo random noise signal generating means and said keying oscillator means for mixing the output signals therefrom, bandpass filter means connected to the output of said balanced modulator means for passing the upper sideband thereof, means for receiving an electrical pseudo random noise signal, transducer means, said transducer means being capable of broadcasting acoustical energy upon excitation by the upper sideband from the aforesaid bandpass filter means and in proportion

Abstract: A digitally controlled oscillator is provided with a memory, storing the half periods T.sub.i (i=1, 2, ..., n) of corresponding frequencies f.sub.i =1/(2T.sub.i) to be generated, and with a digital feedback circuit, in which circuit the half periods taken from memory are decreased by a fixed time value .tau. on a time sharing basis, and in which circuit, as soon as the residual values .DELTA..sub.i,1 =T.sub.i -k.sub.i,1 .tau.<.tau. are obtained, these residual values are increased by the corresponding half periods T.sub.i also on a time sharing basis, and each value so increased is repeatedly decreased by the fixed time .tau.. On repeating this process j times, the residual values can be expressed by: .DELTA..sub.i,j =T.sub.i +.DELTA..sub.i,j-1 -k.sub.i,j .tau., where each k.sub.i,j is so large that 0.ltoreq..DELTA..sub.i,j <.tau.. The digital feedback circuit is connected to n residual value counters, which are each supplied with a series of residual values .DELTA..sub.