I am getting a Compadre with the 5.75" coil and found someone with a 8" brown round concentric coil. I am going to put the 8" coil on the Compadre and give it a test, been curious to see if depth would be increased and sensitivity remains as good as with the smaller coil. When I get the Compadre and the other coil and get the time to get the bigger coil installed I will post a picture and let you's know my thoughts on how well it works.