Broadcast system for a control signal with interference reduction

Claim 2

A broadcast system for transmitting a control signal from the sending side to the receiving side to trigger the receiving side by the control signal, comprising: elimination means for eliminating the same frequency components as the control signal from a broadcast program signal being transmitted through a transmission medium of the broadcast system; detection means coupled to the path of the broadcast program signal to detect from the broadcast program signal a false signal having the same frequency as the control signal before the receiving side is spuriously triggered by the false signal, the detection means comprising selection means for selecting the same frequency signal as the control signal from the broadcast program signal, and measuring means for measuring the duration of the same frequency signal selected to generate a control output only when the continuous duration of the same frequency signal selected exceeds a first predetermined time less than the regular duration of the control signal; and control means coupled to the elimination means and the output of the detection means to insert during only a predetermined second time said elimination means into the path of the broadcast program signal in response to the control output generated from the measuring means of the detection means.

Claim 3

A broadcast system according to claim 1, in which said measuring means comprises a capacitor, charging means for charging the capacitor from the start of the same frequency signal selected by said selection means, discharging means for discharging the capacitor from the termination of the same frequency signal selected by said selection means, and means for generating the control output when the charged voltage exceeds a reference threshold level.

Claim 4

A broadcast system according to claim 1, in which said measuring means comprises first input means for generating a first pulse train only the duration of the same frequency signal selected by the selection means, second input means for generating a second pulse train only the intermittent time of the same frequeNcy signal selected by the selection means, a counter for counting the number of pulses of the first and second pulse trains from the start of the first pulse train to generate a first output when the counter counts a first predetermined number of pulses corresponding to the first predetermined time and to generate a second output when the counter counts after the first output a second predetermined number of pulses corresponding to second predetermined time, first resetting means for resetting the counting state of the counter when the duration of the same frequency signal selected by the selection means is terminated before said generation of the first output of the counter, and second resetting means for resetting the counting state of the counter by the use of the second output of the counter, whereby the first and second outputs of the counter are applied to the control means to determine the second predetermined time so that this second predetermined time starts from the first control output and terminates at the second control output.

Claim 5

A broadcast system for transmitting a control signal from the sending side to the receiving side to trigger the receiving side by the control signal, comprising: elimination means for eliminating the same frequency components as the control signal from a broadcast program signal being transmitted through a transmission medium of the broadcast system; means for generating control pulses each having a duration more than a maximum allowable intermittent time for detecting continuity of the control signal, at the receiving side said control pulses being generated every period less than the regular duration of the control signal; and control means coupled to the elimination means and the output of the just preceding means to insert during only a predetermined time corresponding to the duration of each of the control pulses said elimination means into the path of the broadcast program signal in response to each of the control pulses.

Claim 6

A broadcast system for transmitting a control signal from the sending side to the receiving side to trigger the receiving side by the control signal, comprising: elimination means for eliminating the same frequency components as the control signal from a broadcast program signal being transmitted through a transmission medium of the broadcast system; means for generating control pulses each having a duration more than a maximum allowable intermittent time for detecting continuity of the control signal, at the receiving side said control pulses being generated every period less than the regular duration of the control signal; and control means coupled to the elimination means and the output of the just preceding means to insert during only a predetermined time corresponding to the duration of each of the control pulses said elimination means into the path of the broadcast program signal in response to each of the control pulses.