| 摘要 |
551,664. Party-line systems. STANDARD TELEPHONES & CABLES, Ltd. Aug. 22, 1941, No. 10734. Convention date, Aug. 29, 1940. [Class 40 (iv)] [Also in Groups XL and XX] A party-line substation includes a gas-filled discharge tube TT having an electrode 4, Fig. 1, made as a vibratile magnetic reed, which, when a coil 7 is supplied with current at its natural frequency, vibrates with sufficient amplitude to allow a discharge between electrodes 4 and 5. A ringer R, Fig. 5, gravity switch GS. and tube TT are placed in series across a party line A, B. When current of the frequency appropriate to the tube TT is applied to the line. it passes through coil 7 and condenser C, causing the tube to break down and operate ringer R. When gravity switch GS is raised by removal of receiver, an operator can verify the identity of the answering station by again applying the ringing frequency, when tube TT will earth the B line if correct. |
