JPS57112142A - System for discrimination of training signal - Google Patents

Abstract

PURPOSE:To improve the durability against momentary break of the system, by detecting that the level of frequency components of a binary signal, which is included in a training signal preceding phase modulation data, is constant to discriminate the training signal. CONSTITUTION:When a training pattern having a frequency spectrum of 1.7kHz carrier and its both side-bands 0.5kHz and 2.9kHz, this training pattern is demodulated by multipliers 91 and 92 to become a signal of 1.2kHz and becomes further a signal of 2.4kHz by absolute value square circuits 111 and 112 and is multiplied by the control output of an AGC loop ina multiplying part 15 to become a signal of a constant level and becomes a DC output by an effective value detecting circuit 19. Similarly, the carrier becoms a DC output by an effective value detecting circuit 20. These DC outputs are added by an adder 27 and are integrated by a time constant circuit 28, and simultaneously, their average value is obtained by an average value detecting circuit 30; and when the average value is subtracted from the integral value by an adding part 31, an output (G) becomes a constant value A. When data is inputted, a positive value is added to the output (G) gradually.