| 摘要 |
PURPOSE:To attain complete protection of a pseudo signal and momentary termination of operation and to obtain a receiver quick in restoring the operation by applying two discrete Fourier transform (DFT) of narrow window time and by assuming a logic to remove, from the two outputs of the above, signals other than that of its own channel as well as removing the attenuation and utilizing the narrowness of the window time. CONSTITUTION:When a digital signal of 125mus-sampling is inputted, the DFT 1 executes the DFT calculation with a square-wave window of 8.25ms (66 samples), but the DFT 2 executes the DFT calculation with an inverse Hamming window. The results of said two DFT operations are compared by a selector circuit S. If the absolute values of the two values exceed a value set by a level-difference threshold-setting circuit TH1 (for instance 6dB), the signal is decided as a nonsignal, but if less, the smaller one of the two values is selected for each channel. Next, the operation results in respective frequency channels are compared with each other by a threshold comparing circuit R, and whether to receive or not to id decided as to the respective frequency channels, and the result is inputted to a 3/3-protection logical circuit P in order to execute the protection for the memontary termination and pseudo signal. |
