Telecommunications system output switching circuit - has pilot detector with constant signal to noise ratio at output

摘要

The switching circuit, for switching a telecommunications system's outputs when a given noise level is reached, has a filter to retrieve the pilot signal monitoring the transmission path and a rectifier diode to demodulate the pilot signal and pass it to a detector. A high pass filter (HPe with a cutoff frequency of about 0.44 df, where df is the bandwidth of noise signal before demodulating, is connected between the demodulator (D) and the detector (V, G, A, a). The cutoff frequency is chosen such that the same signal to noise ratio always appears at the output of the detector irrespective of pilot amplitude, except when the pilot is absent or when there is no noise.