Patent GB-1113151-A (GB)
Title: Improvements in diversity radio direction finding systems
IPC: H04B7/02
Filed: 1955-12-10
Abstract: 1,113,151. Radio direction-finding. S. H. W. BROWNING and J. BUCKINGHAM. 7 Dec., 1956 [10 Dec., 1955], No. 35537/55. Heading H4D. A diversity radio direction-finding system comprises two or more stations each having a direction-finding aerial array together with a receiver, the outputs of the receivers being brought substantially into phase alignment and combined into a single display. In one arrangement a station includes an Adcock aerial system and a twin-channel receiver which produces outputs proportional to sin # sin (wt + α) and cos # sin (wt + α), where # represents the direction of arrival of the signal. One of the signals is altered in phase by 90 degrees and then added to the other in the unit Q, Fig. 2, to produce a signal cos (wt + α - #) which is heterodyned with a local oscillator signal sin pt in modulator M1 to produce sin (pt - wt - ½ + #), the sum frequency being eliminated by a filter. This signal is then heterodyned in modulators M2 and M3 with the original input signals to give output signals sin # cos (pt + #) and cos # cos (pt + #). At a second station where the direction of arrival is # the signals are similarly treated to produce outputs sin # cos (pt + #) and cos # cos (pt + #); thus the phase difference is # - # which is normally sufficiently small to allow the signals from the two stations to be added directly and fed to a cathode-ray tube display; the output from a third station may also be added in the same way. In this system the output frequency is the local oscillator frequency and is independent of the input frequency. In another arrangement, Fig. 3, signals at number 1 station are heterodyned with a local oscillator signal in pt to produce outputs sin # cos (wt - pt + α) and cos # cos (wt - pt + α) which are combined in phase quadrature in Q 1 to produce cos (wt - pt + α + #). At station number 2 the arrangement is similar to that in Fig. 2 except that the signal cos (wt - pt + α + #) from station 1 is used in place of a local oscillator. The outputs from station 2 are sin # cos (wt - pt + α - # + # ) and cos # cos(wtpt + α - # + #) and are directly added to those of station 1 in the display E. In this system station 1 is a master station so that if it fails or fades then station 2 and any other station used will also fail or fade; the output frequency is dependent on the signal frequency which may be an advantage. Fig. 4 shows a circuit diagram of the converter unit shown in Fig. 2. The inputs are fed through cathode followers V1, V5, V7, V8 to modulators M2, M3 and to the phase quadrature addition circuit which comprises condensers C1, C2 with resistances R1, R2, the addition occurring at the grid of V2. Biased limiters D1, D2, D3, D4, following V2, V3 ensure constant levels and waveforms at modulator M1 with varying input levels. Local oscillations are fed through a phase shift circuit C6, L6 to modulator M1 the output of which is fed through a filter and valve V4 to modulators M2, M3. The outputs of modulators M2, M3 are added to the outputs of similar modulators through connections A1, A2 and fed through amplifiers V9-V12 to the deflection plates of a cathode-ray tube.