A method and a device for jamming television signals

Claim 1

A method for jamming each of M (M 1) television signals of M television channels to be supplied via a controlled access medium to subscribers who are not allowed to receive at least one of said M television signals comprises a horizontal synchronization signal and being modulated onto a dedicated carrier wave, said method comprising the following steps : - generating a jamming signal ; - forming a jammed television signal by combining said jamming signal with said television signal ; - supplying said jammed television signal to said subscribers ; characterized in that a i-th (1≦i≦M) channel of said M television channels is selected and in that for said i-th channel said jamming signal is formed with a duration equaling the time duration between two successive synchronization pulses of the horizontal synchronization signal divided by M, said jammed television signal being formed by coupling the jamming signal of the i-th channel with the carrier wave of the i-th channel, and in that for said selected i-th channel there being selected among said subscribers those who are not allowed to adequately receive said i-th channel, the operations for said i-th channel being thereafter each time applied to each further (M-i)-th channel until all M channels have been considered, and thereafter said operations being each time repeated for each of said M channels.

Claim 2

A method for jamming each of M (M 1) television signals of M television channels to be supplied via a controlled access medium to subscribers who are not allowed to receive at least one of said M television signals comprises a horizontal synchronization signal and being modulated onto a dedicated carrier wave, said method comprising the following steps : - generating a jamming signal ; - forming a jammed television signal by combining said jamming signal with said television signal ; - supplying said jammed television signal to said subscribers ; characterized in that a i-th (1≦i≦M) channel of said M television channels is selected and in that for said i-th channel said jamming signal is formed with a duration equaling the time duration between two successive synchronization pulses of the horizontal synchronization signal divided by M, said jammed television signal being formed by coupling the jamming signal of the i-th channel with the carrier wave of the i-th channel, and in that for said selected i-th channel there being selected among said subscribers those who are not allowed to adequately receive said i-th channel, the operations for said i-th channel being thereafter each time applied to each further (M-i)-th channel until all M channels have been considered, and thereafter said operations being each time repeated for each of said M channels.

Claim 5

A method as claimed in claims 1, 2 or 3, charac­terized in that said jammed television signal being generated at central station provided for supplying said television signals on said controlled access medium.

Claim 6

A device for jamming each of M (M≧1) television signals of M television channels to be supplied via a controlled access medium to subscribers who are not allowed to receive at least one of said M television channels, each of said television signals comprises a horizontal synchronization signal and being modulated onto a dedicated carrier wave, said device comprising, first means for generating a jamming signal, second means for forming a jamming television signal by combining said jamming signal with said television signal and third means for supplying said jammed television signal to said subscribers, characterized in that said device further comprising selection means for selecting each time an i-th (1≦i≦M) channel of said M television channels, and wherein said first means being provided for forming for said each of said i-th channel said jamming signal with a duration which equals the time duration between two successive synchronization pulses of said horizontal synchronization signal divided by M, said second means being provided for forming said jammed television signal for each of said i-th channels by coupling said i-th jamming signal with the carrier wave of the i-th channel, said device also comprising further selecting means for selecting for each i-th channel among said subscribers those who are not allowed to adequately receive said i-th channel.

Claim 7

A device for jamming each of M (M≧1) television signals of M television channels to be supplied via a controlled access medium to subscribers who are not allowed to receive at least one of said M television channels, each of said television signals comprises a horizontal synchronization signal and being modulated onto a dedicated carrier wave, said device comprising, first means for generating a jamming signal, second means for forming a jamming television signal by combining said jamming signal with said television signal and third means for supplying said jammed television signal to said subscribers, characterized in that said device further comprising selection means for selecting each time an i-th (1≦i≦M) channel of said M television channels, and wherein said first means being provided for forming for said each of said i-th channel said jamming signal with a duration which equals the time duration between two successive synchronization pulses of said horizontal synchronization signal divided by M, said second means being provided for forming said jammed television signal for each of said i-th channels by coupling said i-th jamming signal with the carrier wave of the i-th channel, said device also comprising further selecting means for selecting for each i-th channel among said subscribers those who are not allowed to adequately receive said i-th channel.

Claim 9

A device as claimed in claims 5 or 6, characterized in that said jammed signal is a frequency modulated signal.

Claim 10

A device as claimed in anyone of claims 5-7, characterized in that said first means comprises an inductor-capacitor oscillator circuit.

Claim 11

A device as claimed in anyone of claims 5-8, characterized in that said selecting means being connected to coupling means belonging to said second means.

Claim 12

A device as claimed in anyone of claims 5-9, characterized in that said further selective means comprises a series of signal switches, an output of which being each time connected to an output of a television signal splitter circuit.