GB842437A - Improvements in or relating to delay line arrangements - Google Patents

Abstract

842,437. Delay-lines. TELEFUNKEN G.m.b.H. Nov. 4, 1958 [Nov. 27, 1957], No. 35455/58. Class 40(8). A delay line is combined with means responsive to an applied control voltage for varying the reactances of series and shunt reactance elements included in said line to vary the delay time thereof, the relation between the variation of the reactances of the series elements and that of the shunt elements being such that the surge impedance of the line is maintained substantially constant over the range of delay time variation. The series reactances are preferably inductances consisting of coils wound on magnetic cores the magnetization of which is varied by subsidiary coils. The shunt reactances are preferably semi- conductor diodes, e.g. Zener diodes, the capacitance of which is dependent on an applied D.C. voltage. Alternatively, condensers having dielectrics whose dielectric constant depends on the applied field intensity, e.g. ferro-electric substances such as barium titanate, Seignette's salts, and certain phosphates, may be used, or idle current valves or transistors. The line shown comprises a number of # sections each consisting of a series inductance I and two shunt condensers 2. Each inductance 1 has a ferromagnetic core 3, preferably of ferrite, with a magnetizing winding 4. Input and output terminating resistances 6 and 9 are connected to input and output terminals 5 and 8 and to the line through blocking condensers 7 and 10. A control unit 11 supplies direct current to the windings 4 and. direct voltage to the condensers 2 in response to a control voltage applied to an input terminal 12 so that the input and output surge impedances of the line always equal the values of the resistances 6 and 9 respectively. The delay line may alternatively comprise a number of bridged T sections (Fig. 2, not shown). A suitable control unit is described in combination with a delay line in which the series inductances have a third winding to compensate for the effects of stray leakage and capacitance, and the shunt reactances are Zener diodes (Fig. 3, not shown). To avoid interaction in cases where the control signal contains frequency components within the frequency range of the signal to be delayed, a symmetrical delay line may be employed with a pushpull voltage supply to the Zener diodes (Fig. 4, not shown) or a symmetrical supply via T- connected sets of resistances (Fig. 5, not shown). Alternatively, undesired action of the control signal on the main signal in an unsymmetrical delay line may be prevented by utilizing a compensating voltage derived from the control unit (Fig. 6, not shown).