SYSTEM METHOD, TEST SIGNAL, TRANSMITTER AND RECEIVER FOR REDUCING EFFECT OF DIFFERENTIAL DISTORTION OF THE COMPOUND TELEVISION SIGNALS

摘要

A broadcast system is provided in which the effects of differential distortions on composite television signals are reduced. At predetermined intervals, the broadcast signal includes a test signal having high frequency components at at least three average video signal levels. In a suitably equipped receiver, following demodulation by the receivers vision demodulator (20), a test signal is identified by a test signal detector (34). Measurement apparatus (24) then measures the distortion of the test signal at a number of different average video signal levels, calculates the correction required to minimise the effect of distortion at each measured signal level, and stores the corrections in a memory (28) at address locations derived from the demodulated signal by a filter circuit (32). The stored corrections are applied to an interpolator (40) which derives further corrections for other average video signal levels, the derived corrections being applied to subsequently received television signals by a controllable equaliser (38). IMAGE