Radio direction-finding

1,126,290. Radio direction finding. MULLARD Ltd. 15 May, 1967, No. 22538/67. Heading H4D. The Specification describes a radio direction finder of the type having two orthogonally positioned " figure-of-eight " loop aerials SL and BL mounted on a rotatable assembly S/B and a fixed omnidirectional aerial V. By adding the output of aerial V, after phase quadrature shifting at Z, to the outputs of aerials SL and BL by means of windings SC and BS, switch FV under the control of pulses V1 switching the added outputs between inphase and antiphase conditions, four mutually orthogonal cardioids SN, SS, BW, BE are produced. Thus, if, with the cardioids aligned as shown, the bearing of the incoming radio signal is +30 degrees then the bearing cardioids BE and BW give responses E2 and E3 respectively. These responses are sampled by gated amplifier AB by means of gating pulses BE and BW, Fig. 5, and a signal indicating (E2-E3) appears across indicator BI. Such a signal is ambiguous, representing (180-30 degrees) as well as 30 degrees. To remove the ambiguity, responses E4 and E5 are sampled in amplifier AS from the sense cardioids SN and SS and on determining from the resultant difference signal across indicator SI, that E4 >E5 it is evident that the bearing is 30 degrees. The aerial assembly can then be rotated until E2=E3=E1 to a position giving the bearing.