| 摘要 |
<p>Apparatus for testing telephone instruments to detect an irregular condition therein, for example, an additional listening device or additional wiring which may cause the instrument to be "bugged". The apparatus includes a four-arm bridge network having two resistor arms, a third arm in which the telephone instrument may be connected and a fourth arm including a plurality of condition-simulating devices, such as lamps, buzzers etc. Under normal conditions when testing a telephone instrument, any particular line should be at balance when the proper condition simulating device is connected in the fourth arm but any unbalance may well be indicative of an irregular condition such as an additional listening device in circuit.</p> |
