Polarised repeating coil for telephone lines - has improved magnetisation and return loss characteristics using diode bridge feed

摘要

The repeating coil circuit for coupling a branch extension with an exchange provides improved return-loss damping and reduction in number of bulky and expensive components. On the extension side of the repeating coils (N) the local DC supply is applied through balancing resistors (R1-2) across a blocking capacitor (C3) connected at the mid-point of the windings (W5-6). At the exchange side of the coils (A) only a single winding is used (W7) which is connected across a diode bridge (GL). The opposite arms of the bridge (g3) (g4) are connected to the line (a') (b'). DC current flowing in the line, through the action of the diode bridge, flows through the winding (W7) in one direction only, improving the initial magnetisation of the repeating coil.