Abstract: A narrow band noise cancellor and signal correllator which obtains an increased signal to noise ratio of a received signal from a multi sensor array; the resulting output signal is at double the input frequency. A pair of narrow band similar input signals are added, and subtracted, and the resulting signals are multiplied together. The positive and negative product terms of the signal are separated and the positive term inverted, and the resulting separated signals are individually added with the squared representation of one of the input signals. The resulting added signals are summed and the sum is passed through a narrow band filter having its center frequency at double the input frequency.

Abstract: A time averaging circuit which increases significantly the signal to noise ratio of a received signal. The output of a multiplier which provides near D.C. signals with the noise is fed to a metal core transformer through an operational amplifier. The secondary winding output of the transformer is partly subtracted from the input in the operational amplifier, enhancing the D.C.-like signal components. Time integration via the feed back loop results in the A.C. noise components being relatively reduced in amplitude. The A.C. noise components from the secondary of the transformer and the output of the operational amplifier are subtracted in a second operational amplifier, the output signal of which has substantially increased signal to noise ratio. A pre-processing circuit includes a multiplier which multiplies the received signal with a narrow band-width portion thereof, tuned to the signal frequency, which enriches the near D.C. energy.

Abstract: In sound target detection equipment, at least three microphones are used in a broadside array manner to ascertain the presence of a selected sound source. The outputs of the three microphones all include the sought signal S and respectively contain noise components X, U and Y. These outputs are combined to provide X-U and X-Y. These two signals are then applied as separate inputs to a discriminator which applies the rules:(a) when the input signals are both of the same polarity, the discriminator selects the input closer to zero and presents it as the output;(b) when the input signals are of opposite polarity, the device presents zero as the output.The output from the discriminator is then subtracted from one of the original microphone outputs in a manner tending to cancel out the noise contents, and the resulting signal examined for the presence of the sought signal S. The invention is applicable also to non-aural signal detection equipment.