And neither [RDF or ADF] will indicate whether you are going toward or away from the station without the "sense antenna".
This comes up all the time, the erroneous idea that you can't resolve the "180 degree ambiguity" without a sense antenna. You can, it is easy, and every pilot knows how to do it. Let's say Earhart has been traveling directly towards Howland and listening for the "A's" (dit dah, dit dah, dit dah......) from Itasca. She is now about 200 NM from Howland according to Noonan's dead reckoning, about 1730 Z. She starts to hear them but they are still to weak for her to get a minimum. Now it is 1745 Z and the signal is loud enough for her to get a minimum. She gets two minimums, one with the loop indicator 20° to the right of the nose and the second one at 20° to the left of the tail. Which is the correct bearing? Well, duh, the one in front of the plane is the only possible correct bearing because for the bearing behind the plane to be correct they would have had to have sneaked past the Itasca without hearing anything. The DR shows them approximately 170 NM short of the Itasca so we know this isn't the case so, for this scenario, there
is no ambiguity to resolve. So just turn 20° to the right, the bearing is then right on the nose and you are on your way directly towards the Itasca. This is the most likely scenario for Earhart's approach to Howland.
But what if when you first get a null, the bearings are straight out to the side, over the wingtips? Then you do have an ambiguity since you might have missed the island either to the right or to the left so either bearing could be the correct one. Oh! what to do?
It's simple, just continue straight ahead. The bearings will change and the correct one will swing towards the tail. The incorrect one will swing towards the nose. Here is an analogy that might help you remember this. Let's say you are driving your car down the street and you see a really hot chick standing on the sidewalk on the other side of the street, about 45° degrees to your left. Which way does you head swing to follow her as you drive by? It swings counterclockwise, to the left, towards her tail.
If the original bearing is somewhere in between then just turn the plane to place the bearings over the wingtips, hold that heading for a few minutes and look for the one that swings towards the tail.
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