Patent GB-859118-A (GB)
Title: Improvements in or relating to apparatus for vectorially determining an alternating voltage
Inventor: JR CHESTER B WATTS
IPC: G01R13/20
Filed: 1957-03-19
Abstract: 859,118. Phase measurement; voltage measurement; attenuation / frequency measurements. ALFORD, A. March 19, 1957 [March 19, 1956], No. 8990/57. Class 37 Apparatus for determining the phase angle and magnitude of an unknown signal relative to a reference signal comprises first and second hybrids each having a series feed input, a parallel feed input and a pair of load terminals, such that the input voltage to the parallel feed appears at the respective load terminals in equal magnitude and phase while the input voltage to the series feed. appears thereat in equal magnitude but opposite phase when the said load terminals are terminated in equal impedances; means for applying equal magnitude quadrature components of one of said signals respectively to corresponding inputs of said first and second hybrids, means for applying equal magnitude in-phase components of the other of said signals respectively to the remaining inputs of said first and second hybrids; and means for vectorially combining the output signals from the respective pairs of load terminals of said first and second hybrids to derive signals representing mutually perpendicular vectoral components of the unknown signal. In Fig. 1, a radio frequency signal source G energizes a network D having output 1 at which a reference signal appears and output 2 at which appears an unknown signal to be vectorially compared therewith. The reference signal is divided by network L, C into two equal quadrature signals Er, Er<SP>1</SP> which are connected over outputs 80, 81 to the parallel branches P, P1 of hybrids 5, 6 which are fed with the test signal from G over their branches S, S<SP>1</SP>, so that the input signals to the parallel branches appear at load terminals I, II; I<SP>1</SP>, II<SP>1</SP> in equal magnitude and phase, while input signals to the series branches appear thereat in equal magnitude but opposite phase. The load terminals are connected respectively over similarly poled crystal rectifiers 7, 8; 9, 10 to energize opposedly the primaries of transformers 11, 12 feeding output terminals 22, 23, 22<SP>1</SP>, 231, with voltages which are shown to be respectively proportional (Figs. 3, 4 not shown) in magnitude to the inphase and quadrature components of the unknown input voltage and which may be applied to deflect the spot of a C.R. oscillograph in the X and Y directions to display the input voltage as a line representing magnitude and phase angle by its length and angular disposition. The unknown signal may be modulated (Fig. 2 not shown) by interposing a hybrid whose load terminals are alternately opened and shortcircuited by a mechanical chopper or by a pair of similarly operating D.C. controlled crystal rectifiers, whereby the signal passing through the hybrid is subjected to alternate phase reversal and the resultant signals of amplitudes proportional to the X and Y components of the unknown input at the secondaries of the transformers are shunted by relays synchronised with the modulation, so that the output voltages are zero during alternate excursions of each square wave and are proportional to the total swing of the squarewave during the remaining excursions, and are applied to the respective deflection terminals of a D.C. oscillograph to produce a first display spot at the origin and a second at the termination of the vector representing the unknown signal in magnitude and phase angle. The reference signal may be swept over a test frequency band while maintained at a constant amplitude (Fig. 2 not shown), while hybrids 5, 6 may be replaced by balanced detectors (Fig. 5 not shown). Specification 859,119 is referred to.