Abstract: A correlator comprises a mixing stage receiving a low level signal to be correlated and a 500 KHz square wave. The output from the mixer comprises the low level signal coupled with the 500 KHz square wave signal. This output signal is fed to a multiplier for multiplying with the high level signal to be correlated. The output from this stage is fed via ac coupling to a double balanced mixer also receiving the 500 KHz square wave signal. This stage operates to decouple the square wave signal from the input to that stage to produce a dc output signal. In this output signal the effects of the square wave signal on the correlation itself have been cancelled whereas any spurious signals from within the correlator have in effect been multiplied by negative or positive values. Thus, subsequent integration of the dc output signal produces an eventual correlation output wherein the effects of the spurious signals have been substantially reduced by cancellation.

Abstract: The invention relates to a device for simulating multipath interference in order that the correction stages of a radio receiver can be tested. The device includes parallel paths, simulating the multipath environment, and a pilot tone generator for introducing pilot tone into the paths. A feedback loop continuously adjusts the phase and amplitude of segments in the paths so as to cancel pilot tone from the output whereby the loop maintains the adjustment need for maximum attenuation at the frequency of the pilot tone.

Abstract: A circuit for cancelling unwanted components in two received signals has a first input for one of the signals and a second input for the other. The first input is connected by a first circuit path to an output and the second input by a second circuit path to an output. Each circuit path has an associated feedback which includes a correlating device which is arranged to receive fractions of both output signals. Each correlating device forms a control signal which is applied to a mixer. Each mixer operates under the control of the control signal to feed to its associated circuit path a signal which tends to cancel the unwanted component.