Wind Vane Dead Spots

I have a wind vane that I purchased a couple months ago or so and just deployed outside. I'm finding that it has deadspots in the readings. There are 2 arcs that read 3.3V and 2 arcs that read 0V and they are each about 15-20 degrees each. One of them is from 189 degrees to 172 degrees which is pretty much dead south. 

The angles may not be exactly right because it's a bit difficult to get the exact angles with it mounted on a pole. 

Am I doing something wrong or do I just have a faulty vane?


Thanks