RESTRICTED ACCESS TELEVISION TRANSMISSION SYSTEM AND THE METHOOD THEREOF

摘要

The invention resides in a Television Signal Transmission Security System which provides a higher degree of security then previously possible by utilizing encoding and decoding technology which effectively prevents pirating by amateurs or experimenters. The television signal transmitted is encoded by injecting one or more interfering carriers (24, 26) in specific frequency slots in close proximity to the video carrier (10). Interfering carriers (24, 26) can be injected either above or below the video carrier (10) between harmonics (41-44) of the horizontal frequencies. Combinations of interfering carriers (24, 26) provide coding techniques making the system virtually pirate proof. The interfering carrier (24, 26) is removed by very narrow band rejection filters (100-113) having a rejection band attenuation greater than about 40dB over bandwidth of up to 4000Hz and a 3db bandwidth of approximately 5kHz. The filters (100-113) are constructed using advanced technology to produce the quartz crystal bulk resonators or surface acoustic wave filters. Pre-compensation at the transmitter improves overall amplitude and phase response to provide a nearly perfect decoded picture.