Patent GB-784114-A (GB)
Title: Color-telcvision signal-translating apparatus
IPC: H04N11/14
Filed: 1955-12-13
Abstract: 784,114. Television. HAZELTINE CORPORATION. Dec. 13, 1955 [Jan. 27, 1955], No. 35781/55. Class 40 (3). In a colour television system employing separate luminance and chrominance channels the inherent different transmission. times of which are equalized by means of suitable delay networks, the signals translated by the latter are combined with signals derived from the source supplying the delay networks via filter circuits having the same phase-shift characteristic as the delay networks such that the frequency translating characteristics of the channels are modified in a desired manner. Fig. 1 shows one embodiment in which the frequency translating characteristic of the luminance channel in a colour television receiver is modified so as to accentuate the highfrequency components relatively to the lowfrequency components of the luminance signal. In this arrangement the signals translated by the delay line 30, which serves to equalize the transmission times of the luminance and chrominance channels, are combined in adding device 38 with signals selected by means of a low-pass filter 33 from signals of opposite polarity to those supplied to the line 30, the inputs to the line 30 and the filter 33 being derived from the cathode and anode respectively of valve 32 to the control grid of which the luminance signal is supplied. By suitably selecting the cut-off frequency of filter 33 (the phase-shift characteristic of which, over the range of signal passed, is arranged to be similar to that of line 30) and the relative values of the resistors 39 and 40 in adding circuit 38, the desired overall frequency translating characteristic in which the high-frequency components of the luminance signals are translated at a relatively higher level than the low-frequency components selected by filter 33. This results in the reproduced picture having an improved definition. In a second embodiment (Fig. 5), the desired frequency translating characteristic of the luminance channel is such that signals of the frequency of the chrominance sub-carrier wave are prevented from reaching the luminance amplifier 17 whilst a characteristic similar to that employed in the luminance channel of the Fig. 1, embodiment is, in the present embodiment, employed in the I-section of the chrominance channel. The luminance channel characteristic is realized by combining, subtractively, the signals translated by delay line 30 With signals occupying a narrow band centred around the chrominance sub-carrier frequency and derived by means of the tuned transformer 60 and the desired chrominance characteristic by the arrangement shown in block 56 which is similar to the arrangement described in connection with the embodiment of Fig. 1, and shown in block 16 with the exception of inductance 35 which is included to improve the low-pass characteristic of filter 33. In this embodiment (Fig. 5) the phaseshift characteristics of both filter 33 and of the transformer 60 are also arranged to be similar to the phase-shift characteristic of the delay lines 30 over the range of signals passed.