| 摘要 |
PURPOSE:To secure the pilot signal transmission time shorter than the call signal transmission time and thus ensure a steady transmission to the crosstalk, by transmitting intermittently several types of monitor current having different frequencies in case the picture signal is transmitted to the base band. CONSTITUTION:The marker signal M of the frequency f4 is superposed on the 10th line within the vertical flyback time in the odd field of the TV signal; and the pilot signal P of the frequency f5 is superposed on the 11th line each. The frequency f5 is selected at the level near 4-5MHz, and the frequency f4 is set at about 1/10 f5 or less respectively. With application of this signal to the input terminal 10, the signals M and P are extracted at the output terminal 14 through the M/P extracting transformer 15 plus the M/P detecting circuit 16 and 21. The signal P is compared with the reference value at the comparator 9 after receiving a rectification and then applied to the sample pulse generating circuit 20. Thus the signal P is sample-held 23 by the pulse supplied from the circuit 20, and this output and the comparison signal of the reference value control the variable equivalent unit 12 to apply the AGC. The monitor current is just 0.2% of the TV signal, thus reducing much the effect of the crosstalk. |
