Patent GB-215323-A (GB)
Title: Improvements in telephone repeater and like systems
IPC: H04B3/14
Filed: 1924-03-05
Abstract: 215,323. Western Electric Co., Ltd,, (Assignees of Quarles, D. A., and Mohr, F.). April 30, 1923, [Convention date]. Repeating and amplifying systems.-In an attenuation-compensating telephone repeater system, a repeater is fed from a transformer whereof the primary circuit contains impedances whose effect, as to resonance and damping, is so calculated as to compensate for the attenuation which arises at high and low voice frequencies from the transformer and repeater reactances, and for attenuation at the higher voice frequencies due to the line and to the undesired effect of a lowpass filter at frequencies just below its cut-off. The device also prevents singing at .those frequencies above the cut-off which are not completely suppressed. In the example shown, the amplifier T exerts a substantially infinite impedance in the secondary circuit at low frequencies, such as ringing and low voice frequencies, and the inductance of the primary 3 then has a choking effect. At high voice frequencies, however, the internal capacity of the amplifier T, secondary winding 4, and leads comes into play and is equivalent to a capacitative reactance in the primary 3. In each case undesired attenuation results. This is compensated by inserting a condenser 31 which resonates with the inductance of the primary at low frequency, and an inductance 30 which resonates with the effective capacitance at high frequency, their effects being substantially independent of one another at the frequencies in question. To broaden the resonance a resistance 32 is shunted on the condenser 31 and part of the inductance 30, the latter being adjustably tapped so that the high-frequency damping can be varied. The input voltage is taken from a potentiometer 12 by way of tappings which contain resistances 13 so calculated as to keep the total resistance of the primary circuit the same. for all tappings. A filter 5 of the type shown in Fig. 10 of Specification 186,198 may be inserted in the output circuit of the transformer, and the plate voltage is taken from a battery B with choke 8. The output transformer is shown at 7. In Fig. 2 the abscissµ represent frequencies and the ordinates the " gain " of the repeater system under various conditions. Curve A shows the gain for the uncompensated repeater and transformer. Curve B shows the effect of adding the filter 5, high frequencies being suppressed, while the gain at frequencies just below out-off is undesirablv reduced. Curve C shows the effect of adding the compensator 30, 31, 32, without the filter. Curve D shows the net gain with both filter and compensator, the over-compensation shown at 40 being adapted to counteract line attenuation. The curve B due to the uncompensated filter may rise again as at 28 in the region of suppressed frequencies and so tend to give rise to high-frequency singing. This is checked by arranging for the curve C to fall off substantially as the frequency in question is approached, the combined effect being shown at 29, while in cases where a region is common to the maximal humps 37 and 28 singing is checked by regulating the damping. Specifications 142,115 and 186,198, [Class 40 (v), Wireless signalling &c.], are referred to.