Patent GB-471548-A (GB)
Title: Improvements in and relating to electrical frequency translating devices
IPC: H03C1/58
Filed: 1936-03-06
Abstract: 471,548. Modulating systems. STANDARD TELEPHONES & CABLES, Ltd., HODGSON, K. G., JACOBSEN, B. B., ROBERTS, G. A., and TERRY, V. J. March 6, 1936, No. 6821. [Class 40 (v)] In a frequency-translating device employing one or more rectifiers as modulators, the impedances of the circuit elements are so proportioned that their sum is non-reactive and is of substantially the same value at zero frequency and at the input frequencies p, q, and at the desired output frequency. When the input frequencies are of sine-wave form the effective impedance is of the same value at frequencies zero, 2p, 4p ...., and p Œ q, 3p Œ q, 5p Œ q, ... If the carrier wave p is of square-wave form, the effective impedance is the same at frequencies zero p Œ q, 3p Œ q, .. and 3p, 5p,... The requisite impedance values are obtained by inserting compensating impedance networks. As shown in Fig. 7, two rectifiers 82, 82<1> are fed in series from one source 81 of frequency p, through a transformer 85, and are fed in parallel from the second source 83 of frequency q through a transformer 86 the secondary of which is connected between the mid-points of the input transformer 85 and the output transformer 87. In this common arm the impedance network 95 is inserted for compensating the series impedance 98 and the shunt impedance 97 associated with the rectifiers, at frequencies zero, 2p, 4p .... Closely-coupled impedances 96, 96<1> effect the compensation at frequencies q, p Œ q, 3p Œ q, .... In the form shown in Fig. 9, four rectifiers 62 are connected to form a bridge, and the carrier p is applied through a transformer with secondary coils 67 in all the bridge arms. The other source q is connected through a transformer 70 across one diagonal, and the load 64 is transformercoupled at 73 to the other diagonal. The windings of the transformers 70, 73 connected to the bridge are centre-tapped and connected through a non-reactive impedance 66 of the same magnitude as the impedances of the generators p, q and the load 64 at their respective frequencies, having regard to the several transformer ratios. Fig. 10 shows another bridge modulator with the modulating frequency q applied through a transformer 105 across one diagonal, and the load 104 connected through a transformer 107 across the other diagonal. The carrier p is applied through a transformer 106 between the midpoints of the transformers 105, 107. Each arm of the bridge includes a resistance 114 shunted by a condenser 115 ; and also a winding 116 of a transformer, the fifth coil of which is closed by a resistance 119 of a value equal to the resistive impedances of the generators and the load at their respective frequencies having regard to the transformer ratio. In any form of the invention the impedance networks may contain piezo-electric devices. Capacity in the rectifiers may be compensated by a negative capacity. If the rectifier resistance varies with current, compensation may be effected by inserting non-linear resistances the voltage-current characteristic of which is conjugate to that of the rectifier.