Automatic direction finder antenna preamplifier processor

Claim 1

In a low noise loop antenna means for use with an automatic direction finder, wherein the loop antenna means is comprised of two orthogonal windings and two preamplifiers, one for each said winding, each said preamplifier comprising: a JFET transistor push-pull circuit having at least first and second JFET transistors having source electrodes connected together; means connecting one said winding across the gate electrodes of said transistors; a resistor feedback circuit connecting respectively the drain electrodes of each of said JFET transistors to its associated gate electrode; and output means connected between the drain electrodes of said first and second JFET transistors, the output signal of said preamplifier being taken across said output means; and including means for adjusting the gain of said preamplifiers to be equal to one another; and additionally including first means for mixing the output signal of one preamplifier with a first square wave of predetermined repetition frequency and second means for mixing the output signal of the other preamplifier with a second square wave of the same predetermined frequency but shifted by 90 degrees in phase with respect to said first square wave.