4. ADF's utilize a loop antenna to resolve the bearing of received signals.
The operation of an ADF is chiefly dependent upon the characteristics of the loop antenna.
The loop consists of many turns of insulated wire on a metal form. The incoming radio waves
will induce unequal and opposite voltages on the two sides of the loop. Servo motors will
rotate the antenna to a position where the voltages are equal and opposite - this is the null
A sensing element then reads the position of the antenna, corrects for 180° ambiguities and
displays the information on the #1 needle of the EHSI.
RADIO AIDS TO NAVIGATION