gain modifier 5 and the phase modifier 6 are responsive to the outputs of gain selector phase selector 7 gain selector phase selector 7 includes table in memory of n gains and n phases each corresponding to one of n possible signal spaces usa pseudorandom generator 8 generates pseudorandom number between 1 and n each symbol time these pseudorandom numbers are transmitter to gain selector phase selector 7 which was the pseudorandom numbers as an index into the table in memory of n signal spaces so as to generate the outputs of selector 7 after the signal has been encrypted by modifiers 5 and 6 the signal is conveyed to module 9 wherein it is pulse modulated filtered and modulated by quadrature carriers finally the signal is changed to analog form by converter 10 and is conveyed to communications channel 11 for transmission to a receiver having complementary demodulation modifiers to decode the encrypted signal a typical modem which would include all of the elements of fig1 except elements 5 6 7 and 8 has several fixed transmit functions which manipulate data prior to analog transmission complementary fixed receiver functions are provided to convert this analog transmission into the original error free digital data however in the present invention by using usa generator 8 to provide pseudorandom time varying changes to some of the.