GB469214A - Improvements in wave transmission systems and variable equalizers therefor - Google Patents

Abstract

469,214. Volume control. STANDARD TELEPHONES & CABLES, Ltd. (Western Electric Co., Inc.) Aug. 28, 1936, No. 23645. [Class 40 (iv)] [Also in Group XL] A network for equalizing attenuation is associated with a potentiometer or bridge whereby the output energy of the attenuator is combined with a fraction of the difference between the output and the input energies. The embodiments described differ in respect of the amount of flat loss, or attenuation independent of frequency, which they produce. In a multiplex carrier telegraph or telephone system comprising an equalizer E, which may be of the kind described in Specification 202,284, [Class 40 (iv)], and may compensate for attenuation-variations such as those due to temperature or weather, the input voltage V1 and output voltage V3 of the attenuator E are applied to opposite ends of a potentiometer X, Y, and a variable fraction of the difference (V1-V3), added to the equalizer output voltage V3, is applied to the output amplifier A. In a modification., Fig. la (not shown), a condenser potentiometer replaces the resistance potentiometer XY. The potentiometer may be adjusted manually or by automatic means 16 controlled by a pilot wire. Instead of a valve, a balanced bridge B may be used, Fig. 2. The total output of an attenuator N1 having inverse arms Z1, Z2 is applied through a transformer T2 to one diagonal of the bridge, while a voltage derived from a potentiometer R1, R2 shunted upon one arm Z1, is applied through a transformer T1 to the other diagonal of the bridge. The bridge being balanced there is no reaction between the sources of potential. The outgoing line ZL forms one arm of the bridge and receives a combination of the two applied voltages. The impedances of the system are matched to the resistances of the lines. In a modification, Fig. 3 (not shown), the transformer T2 is replaced by a conductive connection. In a further modification, Fig. 4 (not shown), the potentiometer R1, R2 may, be in series with the arm Z2 instead of being in shunt with the arm Z 1. Alternatively, a differential transformer may be employed, the potentiometer R1, R2 being either in series with the impedance Z2, Fig. 6 (not shown), or in shunt with the impedance Z1, Fig. 5 (not shown), so that the flat loss is eliminated.