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AssigneesL'Etat Francais, Represente par le Secre-d-Etat aux Postes et Telecommunications, La Telediffusion Centre National
InventorsYves M. Noirel, Joseph Blineau, Pierre Leray, Jean-Pierre Bauduin
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This test equipment permits a testing of the demodulator of a teletex television receiver. It consists of a digital test signal generator, the output of which is connected to the HF input of the television, and a receiver, the input of which is connected to the video output of said receiver. The generator tramsmits pseudo-random data packets having a first frequency of binary elements, with two double-intervaled binary elements at two predetermined instants t.sub.1 and t.sub.2 for each packet. The receiver has a data regeneration circuit whose threshold varies line by line from a maximum value to a minimum value. The sampling clock of the receiver is at a second frequency lower than the first by the ratio (n-2)/n, where n is equal to the integral ratio of the first frequency to the line frequency of the television. A suitable means insures resynchronization of the sampling clock at the middle of each line. A receiving circuit for the pseudo-random data detects the errors which are transmitted to the video input of the television.
Test equipment for the demodulator of a teletext television receiver said test equipment being connected to the video input of the television receiver and comprising a digital test signal generator means for delivering pseudo-random digital data packets with a first frequency of binary elements, HF modulator means responsive to said data packets, an output of said modulator means being coupled to an HF input of the television receiver, and receiver means having a data regeneration circuit means with a controllable variable threshold, the input of said receiver means being connected to a video output of the said demodulator, characterized in that said test signal generator means transmits pseudo-random data packets with two double-intervaled binary elements at two predetermined instants t.sub.1 and t.sub.2 of each packet, said data regeneration circuit means including means for varying the threshold line by line from a maximum value to a minimum value, said receiver means also comprising a sampling clock means for providing a second frequency which is lower than the first frequency in a ratio of (n-2)/n, where n is equal to the integral ratio of the first frequency to the line frequency of the teletext television receiver, pseudo-random data reception circuit means for responding to said pseudo-random data packets, and means responsive to the middle of each video picture line for ensuring a resynchronization of the sampling clock means and said pseudo-random data reception circuit means, the output of said resynchronization means providing a digital signal for each detected error.
Dependencies are inferred from the claim text.