Reserve service channel circuit for radio relay communications station - has changeover switch selecting main or reserve path depending on usability

摘要

The service-channel circuit uses a shared demodulator (D) for both the main path (BL) and the reserve path (RL). The demodulator input is connected via a changeover switch (S) to the main path or to the reserve path. The demodulator first output passes to the shared main receiver (E3) and its second output passes to a second receiver (E) that evaluates the pilot signal and detects noise level. This second receiver controls (L) the changeover switch. An astable multivibrator is used to change the switch over repeatedly until either the main or the reserve path is found to be usuable again if at any time both become unusable.