Patent GB-656816-A (GB)
Title: Improvements in or relating to electrical phase-shifting networks
IPC: H03C3/12
Filed: 1948-12-07
Abstract: 656,816. Phase displacing. BROWN, W. J. Dec. 7, 1948, Nos. 31694, 31695, 31696, [Convention dates, Aug. 28, 1947], and 31697, [Convention date, Oct. 15, 1947]. [Class 38 (ii)] [Also in Groups XL (b) and XL (c)] A phase shifting network comprises an inductance and capacitance in series having an output terminal between them and so arranged that as their relative values are changed the phase angle between the voltages across them remains substantially constant and the voltage of that output terminal moves round an arc of a circle in the vector diagram, there being a second output terminal so associated with further circuit elements that its voltage lies at or near the centre of the vector circle. Various circuits are shown in which the latter requirement is achieved in different ways. In some, at the point of maximum sensitivity, i.e. when the voltages across the inductance and capacity are equal in value, the output voltage is 90 degrees out of phase with the source volts (Figs. 8-18) in others, with the greatest difference between the inductance and capacity volts, the output voltage and source voltage are in phase (Figs. 1-7 and 19-23) or slightly out of phase (Figs. 24-28). Fig. 2 is the voltage vector diagram of Fig. 1 when 1 and 2 are the series connected inductance and capacity, and impedances 3 and 6 are resistance and inductive or capacitative and resistive respectively, and O, P are the output terminals. O1 is not exactly at the centre of the circle in the vector diagram around which P1 moves so that as 1 and 2 vary and P1 moves round the circle, the output volts Eout (O1, P1) change a little in magnitude as well as in phase compared with the input voltage Ein. If impedances 3, 6 are tapped inductances (Figs. 4, 5 and 6, 7, not shown), the point O1 can be brought to the centre of the circle. In Fig. 8, series inductance and capacity 1, 2 are connected across taps 14, 15 of an input transformer winding 13 from the ends of which a larger voltage is applied to impedances 16, 17 and split by them into two components at right angles to give the point O<SP>1</SP> in the vector diagram, Fig. 9. Variation of 1 or 2 causes O1 P1 to swing round with constant magnitude. The tappings 14, 15 may not be symmetrical with regard to winding 13 (Fig. 10, 11, not shown), or instead of tappings the inductance 1 and winding 13 may be inductively coupled (Fig. 12, not shown). In Fig. 14, series impedances 1, 2 and 25, 26, which latter have resistances 27, 28 in series (or in parallel, Fig. 17 and 15, not shown), are connected in parallel across the input 24, the characteristics being such as to give vector diagram, Fig. 16. The supply 24 may be inductively fed into inductances 1, 25, Fig. 17 (and Fig. 18, not shown). Fig. 29 is a schematic diagram of the generic form of a network of which Figs. 19-28 (not shown), illustrate specific examples. The rectangles indicate impedances. If 26, 34 are not used O may be the centre tap of an input transformer winding. Fig. 30 shows the application of the phase shift circuit of Fig. 8 to a phase modulated radio transmitter, (see Group XL (c)). The phase of impedances 1, 2 is taken by valves 51, 52 which are arranged to act as inductive and capacitive reactances respectively, and the impedances 54, 55 correspond to 16, 17. A signal from source 43 fed to screen grids 59, 65 of valves 51, 52 varies their impedance values and thereby phase modulates the carrier wave, which, from source 42 is fed to a load through transformer 56. Figs. 31, 32 (not shown), are of phase modulated transmitters using circuits of the kind shown in Figs. 14, 17, there being in each case one valve only to which the signal is fed, the valve acting as capacitance 2. Reference has been directed by the Comptroller to Specification 660,645.