How does a non directional beacon work?

Answer 1

Any directional system have two components, one on ground and one in the air i.e. in the aircraft.

For a NDB the ground station consist of vertical wires(aerials) hanging on the horizontal wire installed on the vertical poles(too much of vertical and horizontal:)).So the transmitted waves are vertically polarized.

Inside the aircraft we have two aerials.First a loop aerial whose vertical members are used to pick up these vertically polarized signals.if the plane of the loop is perpendicular to the incoming signal then the voltage generated in both the ends of the loop is equal and cancel out each other.If the plane of this loop is at any other position than the normal there would a voltage generated which depends upon the cos of the angle shifted from the normal.Thus the voltage generated in the loop is varies with the cos of the angle. A polar diagram representation of the same would generate a figure of eight with one circle of 8 for positive values of cos and one for negative value of cos.Now the meeting points of these two circles are the one where the value of the signal is zero.So from two circles we have now two zeroes or null or the direction from where the signal is coming.to resolve this ambiguity of two direction we position another wire which is known as sense aerial which continues to generate some voltage irrespective of the position of the aerial.if the value of the voltage generated in this wire is represented it would give a circle whose values are all positive.

Now if these two polar diagram are superimposed what we get is cardiod where in the two positive ie one half of figure of eight and circle itself adds and the negative half of figure of eight and this circle brings the so called edge or null of this cardiod, which in turn now tell us the direction of the ground aerial.

if u find it bit complicated , let me know, i would simplify it further.suggestions are always welcomed.

By

Manish Gulia

(manishgulia2008@gmail.com)