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In Part 1, I discussed some generalities in coil performance. In Part 2, I’ll explain how I determine whether a Double-D coil might improve performance in your soil conditions.
My procedure on how to best determine whether you might gain performance by switching to a Double-D coil is the same, regardless of the model of X-TERRA you are using. And this procedure is based on a “ground phase number” representing 30% of the highest ground balance number that your detector is capable of.
This number also represents a phase angle of approximately +2 degrees on each detector. Based on that +2 degree setting, if you can properly set your ground balance on your X-TERRA, (using the stock 9-inch concentric at 7.5 kHz) and obtain a number that represents 30% or smaller of the highest ground balance number available on your X-TERRA, I consider that soil to be highly mineralized and will benefit from using a Double-D coil.
Since the ground balance scale of the X-TERRA 70 and X-TERRA 705 have a maximum ground balance number of 90, I consider 28 to be the “break point” for switching to a Double-D (Approximately 30% of 90). Therefore, when you properly set the ground balance on your X-TERRA 70 or X-TERRA 705, if the ground phase number is 28 or larger, I believe you will find that Concentric coils will provide more stable operation than a similarly sized Double-D.
If, however, the ground phase number is smaller than 28, I believe the X-TERRA 70 and X-TERRA 705 will perform better when implementing the design characteristics of a Double-D coil.
Using the same “30%” rule, since the maximum ground balance number on the X-TERRA 505 is 50; the “break point” would be a ground phase setting of 15. If when you properly ground balance your X-TERRA 505 and have a ground phase reading of less than 15, you should consider using a Double-D coil on that site.
On the X-TERRA 305 and X-TERRA 50, with a maximum ground balance number of 20, the break point would be 6. So if you properly ground balance your X-TERRA 305 or X-TERRA 50 and have a ground phase number of 6 or smaller, you should consider using a Double-D coil at that site.
The X-TERRA 30 has fixed Ground Balance and is therefore not adjustable by the user. However, based on my testing, I am of the opinion that the X-TERRA 30 is factory preset at a ground phase setting of (what would be) 6, representing a +2 degree setting.
In Part 3 of this blog post, I will discuss the differences in target response amongst the three frequencies.
Randy Horton (Digger)
You'll never know for sure......unless you dig it!