GB879376A - Improvements in or relating to apparatus for determining the phase and magnitude of an unknown signal relative to a reference signal - Google Patents

Abstract

879,376. Impedance and phase-angle measurements. ALFORD, A. March 10, 1958 [March 22, 1957], No. 7664/58. Class 37. In apparatus for determining the phase and magnitude of an unknown signal relative to a reference signal, Fig. 2, the output from a sweep oscillator 14 is fed via a matching tee junction 4 both to a hybrid network 3, from which is derived the unknown signal in dependence upon an unknown impedance Zx connected thereto, and also to a polar displayer D, to constitute the reference signal, and wherein it is applied both to a voltmeter-rectifier 16, the output of which is fed back to maintain a constant oscillator power supply 13, and to a phase splitter 17 to provide two orthogonal reference voltages which are fed respectively to hybrid networks 10A and 10B and therein mixed with the output from network 3 through matching tee junction 7. Known Zs and unknown Zx impedances are connected to the hybrid network 3; and the output therefrom, which is proportional to the reflective coefficient of Zx, is fed to a square wave balanced modulator 5 comprising a hybrid network the side arms of which are alternately switched at 60 c.p.s. by high-conductance germanium diodes 20; the modulated output constitutes the input to matching tee 7. The side branches of hybrid networks 10A, 10B are fed respectively to pairs of balanced rectifiers 11, 11, where the square modulation is recovered; the detected squarewave amplitudes being proportional to perpendicular components of the reflective coefficient of Zx. The hybrid networks 3, 5, 10A and 10B are each as shown in Fig. 1, and comprise four coaxial terminal pairs S, P, I, II; the outer terminal of each pair being earthed; the inner terminal of S is connected through the inner conductor of balun coil A to connecting block D, the outer conductor of coil A being connected between connecting block C and the earthed shield F. The outer conductor of a second balun coil B, or alternatively a metal rod, connects block D to shield F and may be shaped as a mirror image of coil A. The inner terminals of inputs I and II are connected respectively to blocks C and D, together with the inner terminal of P by way of parallel resistors R. When terminating load impedances Z0 = R are used, the input to each branch is matched to Z0, without compensation, provided that the characteristic impedance of the inner conductor of coil A is Z0 and that the reactances of coils A and B are large compared with Z0. Specifications 856,030 and 859,118 are referred to.