Abstract: Radio direction finders using the principle of periodic scanning of a circular array inherently display a bearing error related to the group delay through the receiving, detection and evaluation process. Correcting by subtracting a constant .theta..sub.o is simple but it is difficult to keep .theta..sub.o constant. The present invention cancels the group delay error instead of compensating for it with a predetermined constant. Scanning is done at angular velocities .OMEGA..sub.1 and .OMEGA..sub.2 for m turns and n turns respectively. The parameters are related by the formulae.omega..sub.2 /.omega..sub.1 =m/n (1)n-m=1 (2)Group delay errors are cancelled by computing the true bearing from the formulan.theta..sub.2 -m.theta..sub.1 =.theta.where .theta..sub.1 and .theta..sub.2 are the bearing readings at .omega..sub.1 and .omega..sub.2 respectively and .theta. is the true bearing of the radio target.

Abstract: A system comprises two kinds of multiplex stations connected by two wire lines and distinguished by two different predetermined frequency basebands each of which consists of predetermined frequencies for dividing the multiplex channels. The multiplex stations are provided with conversion means in their respective transmit paths so as to convert their own basebands to the different ones of the other multiplex stations connected and vice-versa. The system preferably provides generalized units in both kinds of multiplex stations and is simpler than a known one which uses the same basebands in all multiplex stations and converts the baseband before and after transmitting.

Abstract: A novel Direction Finding system is described, using a small aperture circular array of vertical dipoles, the outputs of which are rotated in phase by angles corresponding to their angular location on the array circle. A phased ring combiner is used to add the dipole pair outputs, giving two resultant waveforms, one advanced in phase and the other retarded by the same angle .theta., where .theta. is the relative bearing angle of the incoming signal. The phasing elements are made independent of the signal frequency either by the use of all-pass networks or by prior conversion to a fixed intermediate frequency. DF processing can be performed by a digital meter which computes the phase difference between the two resultant waveforms. In addition, an orthogonal DF display is available through a .SIGMA./.DELTA. conversion.

Abstract: Disclosed is an electronic signal processing system for an alternating voltage input signal. A phase-locked loop network has an input adapted to receive the signal and produce an intermediate signal comprising a substantially noise free sine wave with a phase equal to the average phase of the input signal. The intermediate signal is applied to an input of a variable gain amplifier which produces an output signal proportional to the intermediate signal, and an amplitude averaging loop network has the input signal and the output signal as its inputs and produces a biasing signal which is applied to a control input of the variable gain amplifier to maintain the output signal equal in amplitude to the average amplitude of said input signal. The system can be used in a Watson-Watt type radio direction finder to eliminate noise.