| 摘要 |
PROBLEM TO BE SOLVED: To adopt a reception method by converting frequencies of a check signal received from a terminal end of a loop line, an foremost signal and a rearmost signal into low frequencies, softwarewise analyzing the check signal, the foremost signal and the rearmost signal, then extracting the same, and comparing the same. SOLUTION: A conversion circuit 14 to convert a high frequency signal inputted from a terminal end of a loop line L into a low frequency is provided between a reception level control circuit 11 and a band-pass filter 12. In an analyzing part 20, after signals whose frequencies are converted into low frequencies at a pre-processing part 10 are respectively converted into digital signals at an A/D conversion circuits 21a, 21b, they are subjected to a detection processing by a specified software at dual analyzing circuits 22a, 22b. With this constitution, the foremost signal fIN and the rearmost singal fOUT modulated are detected, whereby an improved S/N ratio and an excellent noise resistant characteristic are attained.
|
