I am seeing this in a simulator, so I don't have a manual for it…
On the Bendix King KR87 NDB receiver, the leftmost button labelled “ADF” switches an indicator above it from “ANT”
When pushed, the needle on the direction indicator indicates towards the NDB (if in range). When popped, it does not, at least for the NDB stations.
So I am wondering, what does this switch change and why it is needed?
(screenshots taken from FlightGear simulator by me)