An apparatus includes a down hole tool housing attached to a ranging electromagnetic field strength sensor. The ranging electromagnetic field strength sensor is to measure electromagnetic field strength components associated with an electromagnetic field originating at a first well, via at least one of direct transmission and backscatter transmission, when the down hole tool housing is disposed in a second well, to provide ranging measurements to calculate an approximate range between the first well and the second well. The apparatus includes a reference electromagnetic field strength sensor to provide a closed loop current path around the down hole tool housing, to provide distorting field strength measurements.