A communications system which enables enhanced services to be provided over cable TV systems. The design of the system is such that amplification is not required. Therefore, two-way transmission is possible on the low band of "two-way capable" cable systems and intermediate power failures do not affect...http://www.google.com.tw/patents/US4677686?utm_source=gb-gplus-share專利 US4677686 - Passive transmission of data over cable TV systems
