| 摘要 |
1,197,575. Multiplex radio signalling. IN. TERNATIONAL STANDARD ELECTRIC CORP. 7 Sept., 1967 [9 Sept., 19661, No. 40945/67. Heading H4L. The audio IF stage of a television receiver is modified to facilitate the use of integrated circuits. Fig. 1 shows the video carrier 1 of a television signal with its video spectrum 2, the accompanying sound carrier 3 and an adjacent video carrier 4 with its spectrum 5. According to the invention the audio IF is made less than (as described, half) the frequency spacing 6 between the sound carrier 3 and the video spectrum 2, or the frequency spacing 7 between the carrier 3 and the video spectrum 5 if this spacing is the smaller. The intercarrier sound signal at a frequency of 5À5 mc/s is supplied via lead 8 to a mixer 13 the oscillator circuit 10, 11 being tuned to 5À25 mc/s so that an IF output of 250 kc/s is obtained. The coil 11 has a small inductance so that it can be made by a film technique. The IF signal is fed via a low pass filter 19 to 24 to an amplifier which supplies a counter type frequency discriminator. |
