| 摘要 |
A off-premises CATV system includes a compensation control including a picture carrier controlled automatic gain control and an automatic slope control. A broadband television signal output from a variable gain device is distributed by a radio frequency signal splitter to a number of subscribers for interdiction by the generation of a number of jamming signals. The variable gain device and a variable impedance device which is frequency dependent are connected in series for automatic gain control and automatic slope control, respectively. A first feedback control is used to compare a first portion of the broadband television signal to a reference power level and to control the variable gain device to null the error. A second feedback control is used to compare a second portion of the broadband signal to a second reference power level and to control the variable impedance device to null the error. A second embodiment of the second feedback control differences the first and second portions of the broadband television signal. The first predetermined portion is a band of frequencies (high band) between 250 MHz. and 310 MHz. and the second predetermined portion is a band of frequencies (low band) between 54 MHz. and 150 MHz. The predetermined power level reference for automatic gain control is set equal to the attenuation between the off-premises equipment and the subscriber premises plus the desired level at the subscriber premises. The power level of the jamming signals for denying access to unauthorized television programs is set to fall within a predetermined range of power levels related to the first predetermined power level reference.
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