Anyone know what type of large hawk seen in NJ that has a bright white band at the base of its tail?

Answer 1

Marsh Hawk, perhaps.
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Answer 2

It is surely a Northern Harrier, or marsh hawk, assuming that you mean a large white spot on the back or top of the bird where the tail meets the body.
There are several large hawks that may have two or three white bands across the tail, but a single white area is specific to a northern harrier.

Answer 3

If it is brown with reddish wings it is a Harris hawk, or it could be a juvenile of some other species.