Patent GB-437452-A (GB)
Title: Arrangement adapted for maintaining a constant transmission equivalent in a transmission system
IPC: D06M23/00
Filed: 1934-04-30
Abstract: 437,452. Repeaters. TELEFONAKTIEBOLAGET L. M. ERICSSON, 33, Kungsgatan, Stockholm. April 30, 1934, No. 13022. Convention date, May 1, 1933. [Class 40 (iv)] [See also Group XL] The transmission efficiency of a repeating system is kept constant by causing it to oscillate weakly at a frequency outside the signal band by means of a back coupling comprising filters F2, F<1>2 and deriving an amplification or attenuation controlling voltage from the oscillation generated with the aid of detectors D, D1. The four wire system may include a radio link or may be modified for signal transmission by wire or wireless in one direction only, the back coupling for producing singing being provided by a wire channel not employed for signalling or employed for signals independent of the main signals. In a modification, Fig. 3, instead of providing a special connection between the E and W lines, the hybrid coil T is unbalanced for the oscillation frequency by providing on the line side a series resonant circuit tuned to the oscillation frequency and on the balance side a pair of series resonant circuits tuned to frequencies of which the oscillation frequency is the geometric mean. This combination acts as a very high impedance to the oscillation frequency and since the circuit on the line side has a low impedance at this frequency the hybrid coil is unbalanced and the system sings. The control voltage is derived from a circuit F2, D. Each of the amplifiers in the four wire path may be similarly controlled. The control voltage may control the amplifier gain in known manner. The Specification as open to inspection under Sect. 91 comprises also the arrangement shown in Fig. 5 (Cancelled) for controlling an adjustable attenuation network comprising a differential transformer Tk connected as shown to a resistance R and a transformer Tr having its secondary circuit shunted by metal rectifiers S. Normally, the impedance of Tr is much greater than the resistance R and signals accordingly are passed to the amplifier V. A change in conditions such that the amplitude of the oscillation current is increased increases the current through rectifiers S and so brings the impedance of Tr nearer to that of R and reduces the transmission efficiency of Tk. A reduction in the value of the oscillation current correspondingly increases the transmission efficiency. In the arrangement shown in Fig. 1 (Cancelled), the amplifier V is caused to oscillate at any desired strength at a frequency outside the signal band by means of a back-coupling circuit including filters F2 and network K2, currents from which are rectified at Det and passed through a variable network K3 to adjust the biassing voltage on the amplifier V or otherwise to ensure constant gain. This arrangement by the omission of one of the filters F2 and of both the filters F1, which in the system shown keep the control currents out of the signal circuits, is stated to be suitable for generating oscillations of a constant amplitude. This subject-matter does not appear in the Specification as accepted.