Line Protection Switching for the L5 Coaxial System

A new 1-for-10 line protection switching system called LPSS-3 has been developed for the L5 coaxial system. Reliability and economic considerations dictate maximum switching spans of 150 mi. Control is primarily by integrated-circuit logic. The line switches use microwave switching diodes to achieve the required pass, modulation, and isolation characteristics. Switching is initiated when temperature pilot levels deviate ± 5 dB from nominal or when the total system energy increases 9 dB above nominal (system overload is imminent). For release, the pilot must be within ± 2 dB of nominal and total energy must be less than +5 dB above nominal. Interstation signaling is accomplished by pulse code modulating complementary channels. Checking complements and parity lends immunity to error. Retransmission of failed codes is automatic. Complete manual control, both local and via telemetry, is provided.