The E6 Negative Impedance Repeater

1483 1483 1485 1485 1486 1486 1491 1491 1492 1493 1493 1495 1497 1504 1504 l.i The E23 Negative Impedance Electron Tube Repeater One of the methods used to reduce the transmission losses in exchange area cable circuits employs E23* negative impedance repeaters. These repeaters, 1 first installed in 1954, represented a considerable advance over the series-type negative impedance repeaters 2 then in use. The improvement was accomplished by the addition of a shunt-type converter to the existing series-connected negat ive impedance element. Impedance discontinuities introduced into otherwise uniform loaded circuits and the resulting undesirable reflection effects were thereby avoided. The effectiveness of this technique is attested by the fact that over one million E repeater units have been installed in the Bell System since 1954. Installation of the E23 repeater is relatively complex, since the negative impedance of the repeater must be closely matched to the cable impedance in order to give the desired gain and return loss characteristic. The matching is accomplished by strapping components of complex networks included in the repeater. The required strapping varies with (a) the amount of gain required, (b) the cable facility with which the repeater is associated and (c) the length of cable end-section to which the repeater is connected. Network connections for a particular condition are specified by extensive strapping charts. This is a time-consuming operation on the initial installation and on subsequent changes, either for gain or end-section adjustment.