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Aural-Null Direction Finder Guide

A crossed-field amplifier (CFA) is a specialized vacuum tube, first introduced in the mid-1950s and frequently used as a microwave amplifier in very-high-power

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Adrian Sagun
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612 views2 pages

Aural-Null Direction Finder Guide

A crossed-field amplifier (CFA) is a specialized vacuum tube, first introduced in the mid-1950s and frequently used as a microwave amplifier in very-high-power

Uploaded by

Adrian Sagun
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Aural-Null Direction Finder

• 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.

• In this method adjusted quadrature voltage are going to introduce to cancel the picked-up
voltage.

Process of Aural-Null Finder

Continuous Wave Signal

• Carried out by means of the non-directional vertical antenna alone or the loop may be used at
or near its operation.

Bilateral Operation

• The signal is picked up on the loop which has course two directions of null pick up.

• Result is an accurate bearing but with 180° ambiguity.

Unilateral Reception

• Also refer as sense determination or operation with cardioid pattern.

• Signals from the loop and the vertical antennas are combined in proper phase relationship to
give a single null pattern.

Circuit of Shipboard Direction Finder Showing Balancer and Sense Connections


Circuit Operation

• For loop-voltage, there is a series tuned circuit, 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.

• 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.

• 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.

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