# How does an rotating loop determine direction of an station signal

1. Aug 2, 2011

### rajeshmarndi

Considering the ADF (automatic direction finding) of an aircraft.

Assuming the transmitting aerial is vertically polarised i.e mag field lies in the horizontal plane.

And it is the magnetic field of the incoming signal that induces current in the loop.

And what would be the rotating plane of the loop (ADF) ?

I'm not getting a clear picture of the working, any help is appreciable.

2. Aug 2, 2011

### xts

Actually, the detector is not a loop, but many-loops coil with ferrite rod core. But in general it works the same.
As the loop axis points towards the transmitter, no signal is induced. So you just must tune your reciver, then rotate your antenna, and the moment when signal fades is when it points towards the lighthouse.

Of course, the direction is found with 180deg ambiguity. To resolve this ambiguity additional trick must be used, e.g. comparison of signal phase received by two antennas.

3. Aug 2, 2011

### rajeshmarndi

i have little confusion about the axis of the loop. If the axis is vertical and the loop area(vertical) rotate about its axis 360 deg, if i'm right i can see the loop induces current.

But then you said the when the loop axis points towards the transmitter which means the axis is horizontal and is perpendicular to the loop. And the loop is not rotated about its axis but the axis is being rotated in the horizontal plane, because of which the loop area vary to the signal and is max when the loop axis point towards the signal and therefore max current is induced.