| 摘要 |
A cable meter for monitoring the channel selected by a converter of a television system which receives signals by means of cable. The cable is connected to the cable meter and the output of the cable meter is applied to the converter. The output of the converter is connected back to the cable meter which, in turn, provides an output to the television. During normal operation, signals received by the cable meter from the cable pass directly to the converter, and a selected channel from the converter passes through the cable meter to the television. To monitor the channel selected, an oscillator generates a substitution signal which is substituted for the television signal applied to the converter. The cable meter then monitors whether the substitution signal passes through the converter, during which period, the cable meter prohibits this substitution signal from reaching the television. By varying the frequency of the substitution signal, a search is performed for the selected channel. Techniques are employed to enhance the accuracy of the monitoring. The present invention has applicability to any communications system in which radio frequency signals are transmitted over any medium, such as televisions with internal tuners which may not even be adapted to receive cable signals or radio receivers. |
