| 摘要 |
<p>PURPOSE:To improve the detection capability by ORing between the output-side level reduction detection signal and the input-side level increase detection signal of a band-pass filter in a receiving part. CONSTITUTION:If disconnection occurs at a point P, the reflected wave from the point P passes a hybrid coil 5 and an amplifier 7 to become (L-2l-40)dB in the input side of a band-pass filter 8 and is attenuated in the filter 8 by 40dB and becomes (L-2l-80)dB in the output side. Consequently, the range where both detecting circuits 10 and 11 are operated is K<(L-2l)<40-K when detection levels of detecting circuits 10 and 11 are defined as (-40-K) and (-40+K) respectively, and either of detecting circuits 10 and 11 is always operated in case of 0<K<20. Consequently, ORing between both detection signals is executed by an OR circuit 12 to obtain a line disconnection detection signal DE, thereby detecting line disconnection independently of the loss of the line.</p> |
