Cable TV - Jamming

' Jamming ' is simply the injection of an interfering noise or narrow-band signal into the non-critical region of the channel being secured or the bandwidth of the channel. This signal is usually sent from the cable headend along the cable line to the subscriber's house.

The carrier frequency of the injected signal is about 2.25 MHz or 2.5 MHz higher than the carrier frequency of the picture signal, which is where sideband picture information is transmitted.

To remove this injected signal (noise) from the incoming signal before it is converted a notch filter will need to be used to filter out this unwanted portion of the signal.

Thid method is susceptible to loss in some of the video information and also reducing the contast slightly. Although this is a 'loss' in picture quality most subscribers accept it.

The 'jamming' method is not very strong when it comes to single security since notch filters can be easily made and installed without much trouble. This method is no longer used on any of the newer cable systems for obvious reason.

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