Patent GB-570203-A (GB)
Title: Improvements in phase shifting circuit arrangements
IPC: G01S3/14
Filed: 1942-02-04
Abstract: 570,203. Phase-shifting circuits for wireless systems. -JEFFERSON, H. Feb. 4, 1942, No. 1497. [Class 40 (v)] [Also in Group XXXVI] In a direction finder for determining the bearing of a wireless transmitter by comparison of the phase positions of the energy received on two spaced aerials connected respectively to channels A, B, Fig. 2, the energy in each channel is applied through tunable means such as amplifiers RFA, RFB respectively to frequency-changers FFCA, FFCR, where it is combined with oscillations from a local source. This source comprises frequency-changers IFCA, IFCB and respectively fixed and variable frequency oscillators LOC and ILOC connected to them, the connection between the fixed frequency oscillator LOC and the frequencychanger IFCA being through a phase-shifter PA. An equalizer unit EB may be inserted between LOC and the other frequency-changer IFCB. The outputs from the frequencychangers FFCA, FFCB are applied to a cathoderay oscillograph or other phase-comparator CRO. in the form shown by way of amplifiers FIA, FIB. Adjustment of the phase-shifter PA to produce a given relative phase shift between the oscillations applied from LOC to IFCA and IFCB will produce the same relative phase shift in the outputs from them, and hence in the outputs of the frequency-changers FFCA, FFCB, so that the setting of PA necessary to bring these outputs into phase indicates the phase difference of the received transmission in the two aerials. Since only constant-frequency oscillations from LOC pass through the phaseshifter PA, the frequency -shift it produces for a given setting is independent of the carrier or modulation frequencies of the received transmission, and, further, the frequency of the outputs in the two channels can be adjusted by varying the frequency of the oscillator ILOC without varying the phase-relation of these outputs. In a modification, which operates in a similar manner, the frequency-changers IFCA. and IFCB are omitted, and each channel. contains a first frequency-changer connected to the variable-frequency oscillator and a second frequency-changer connected to the fixedfrequency oscillator, in one case through a phase shifter. Either of the above circuits may be used for radiating a beam, the direction of which is determinable or variable by suitably relating or varying the relative phases of the energy radiated by the two spaced aerials, the signals passing through the channels in the opposite direction to that of the received signals and the sense of the amplifiers being reversed. Fig. 4 shows a modification providing oscillations of a common desired frequency, but of different phase, and suitable for providing a beam of desired or variable direction when employed with spaced aerials. An oscillator FLO feeds directly to the output stage OA of channel A, whilst in channel B the oscillations are combined in frequency-changer IFC with those from a variable-frequency oscillator VLO, the output from which is passed through a phase-shifter PB and is then again combined with oscillations from VLO in a second frequency-changer 2FC, thus restoring the original frequency to the phase-shifted oscillations supplied to the output stage OB. The direction of the beam may be varied by alteration of the frequency generated by VLO, which alters the phase-shift produced by PB without altering the frequency of the output from 2FC. A phase-comparator CRO and frequency meter FM are provided.