Recovery of digital information transmitted in scrambled form - is achieved by recovering signal rate frequency from sun of absolute value demodulated signal and its hilbert transform

摘要

In a digital information transmission system, such as in telephony binary signals are scrambled and coded to give the effect of a noise signal and transmitted as modulation on a carrier in single sideband transmission. In the receiver a synchronous quadrature demodulator (9) provides two demodulated signals (x, (+), x2(+) 90 deg. out of phase. The demodulated signals are rectified in respective full wave rectifiers (45, 44) and summed in a summing circuit (47). A threshold circuit (48) eliminates the effects of continuous signal components and applies the signal to a phase lock loop circuit (49) the oscillator (50) of which is held on a frequency spectrum line equal to the binary frequency rate present in the applied signal. Thus the coded and scrambled signal is recovered by summing the absolute value of the demodulated signal with its Hilbert transform. The circuit is relatively insensitive to phase errors securing in demodulation.