GB1177707A - Circuit Arrangement for Preventing Short-Duration Dropouts of a Carrier Frequency Television Signal - Google Patents

Abstract

1,177,707. Television. FERNSEH G.m.b.H. 31 Aug., 1967 [10 Sept., 1966], No. 39934/67. Heading H4F. Specification describes apparatus for avoiding signal drop-outs in the carrier, frequency read out of a video tape recorder and enables the detection of drop-outs of durations less than a carrier period. In the embodiment of Fig. 1, the frequency-modulated carrier read out signal is applied at F and passes to an output 17, either directly or via a one-line period delay 20 depending on switch 30. The " direct " position of switch 30, as shown, is used when no drop-outs are detected, whereas detection of drop-outs by means 40 and 50 cause the switch to move to the delayed (previous line) signal. Means 40 includes a tapped delay line 10 of relay T, where T, Fig. 2, is the carrier period and n the number of tappings. Half-wave diodes rectify the signals S 0 , S 1 , S 2 , S 3 at the tappings such that the signal applied to threshold means 50 is normally formed from the successive peaks of the signals S 0 &c., as shown in solid line in Fig. 2. Means 50 produces a signal, moving switch 30 to its upper position, when its input signal falls below a threshold S. This will happen on occurrence of a drop-out-possibly less than T in duration. In the embodiment of Fig. 3, drop-outs less than a period T in duration are detected by threshold means 50, by converting up the carrier in mixer 12 to a much higher frequency, and detecting absences of peaks in said higher frequency signal.