MULTILEVEL PCM SYSTEM ENABLING AGC CONTROL OF A TRANSMITTED MULTILEVEL SIGNAL IN ANY SELECTED FREQUENCY PORTION OF SAID TRANSMITTED SIGNAL

This relates to a PCM system having a substantially constant power amplitude distributed throughout the frequency spectrum of a digital signal. This enables selecting a suitable portion of the spectrum of the digital signal for operation of the AGC circuits of the system, particularly those AGC circuits contained in predetermined ones of repeater incorporated in the system. To accomplish this, the system includes, in the transmitter, a pseudo-random scrambler operating on a binary signal input to provide the substantially constant power amplitude distributed throughout the frequency spectrum of the input binary signal. The output signal of the scrambler is converted to a ternary signal prior to transmission. At the receiver the ternary input signal is converted to a binary signal. The binary signal at the output of the last converter is descrambled to compensate for the scrambling of the scrambler and to produce a replica of the binary input to the system.