AN AURAL-NULL DIRECTION FINDER

BY:L.A.AASHIKA

ECE A SEC

In this method, Voltage required for sense-finding is given to the loop circuit.

When metallic objects are present ,it produces undesirable voltages in the loop.

Voltages with quadrature phase broadens the null.

So , in this method we are going to introduce a quadrature voltage that is adjusted to cancel the picked up voltage.

INPUT CIRCIUT OF AN AURAL-NULL DIRECTION FINDER

Working: For loop voltage,there is a series tuned

circiut,whereas an additional voltage is introduced by a variable inductive coupling b/w L1 & L3 with switch in position 1.

With the help of C2,L5,C3 the new voltage becomes in phase quadrature with the loop voltage.

Using L1 &L3, the quadrature component from “antenna effect” can be cancelled out.

working

When the switch is in position 2,the current in L4 is in-phase with vertical antenna voltage and voltage in L2 is in phase quadrature to it.

By adjusting R1,a good sense discrimination can be obtained.

So when switch is in ‘balance’ position,L3 inductor sharpen the null whereas when it is in ‘sense’ position, the loop is turned to 90 degree and the sense can be found out.