PAL colour TV decoder - is modified to decode NTSC colour subcarriers by frequency conversion of subcarrier and suppression of alternate line phase inversion

摘要

The decoder circuit (20) is designed to receive the colour subcarrier of a PAL colour transmission system and recover the red, green and blue primary colour signals and is adopted to decode the colour subcarrier of the NTSC system by the addition of a circuit (10) which mixes the NTSC subcarrier of about 3.58 MHz with a 8.01 MHz signal to convert it to a signal at 4.43 MHz, the PAL subcarrier frequency, the converted signal then being fed to the PAL decoder. An electromagnetic controlled switch circuit suppresses the reference wave phase inverter circuit and the line delay circuit of the PAL decoder for the period of one line and substitutes for the signal from the amplitude detector of the decoder on adjustable command voltage controlling the gain of this circuit and activating the colour suppression circuit.