It should first be mentioned that some people confuse an air test with placing a coin on the ground and waving the coil over it. A true air test is actually a bench test, and should not be performed by placing a coin on the ground because the detector will be looking at ground conditions and any other objects in the ground that can cause erroneous readings.

Take a cardboard box approximately a foot high and cut a small "V" shaped section in one side to hold the rod and coil above, and extending beyond the surface of the bench or table, because most tables have metal hardware holding them together. Make sure you have no metal anywhere on your person or within 2 to 3 feet of the search coil.. In the area you're testing, first check for electrical interference that will prevent you from performing an accurate air test. Do this by placing the detector in the fixed ground balance and all-metal modes and adjust the sensitivity to about 8. Adjust the threshold to a barely audible level and listen for a constant threshold tone that should not be fluctuating or wavering badly. At this point, if the threshold tone is wavering or motor boating, you need to identify and stop the source of the electrical interference or move to another location.

Next, set the discrimination control to 3.5 and place the mode switch in disc position. Adjust the sensitivity to where it just starts to chirp (about 9), and back off just a hair. Holding a non-metallic yardstick in front of the coil, wave a coin in front of the coil and take note where it stops giving a repeatable signal as you move the coin away from the coil while continuing to wave it. Note: The audio signal will become weaker as the target is moved away from the coil. This is normal because this is the built-in audio modulation which is very useful when trying to determine deep targets vs. shallow targets, and when searching in heavy trash. Also, the coin should be held flat.

If done properly and in an optimum environment, the X5 with the 9" concentric coil or the 10 x 5 DD coil should produce an air test on a quarter at 15 to 16 inches and a nickel at 14 to 15 inches, assuming there is minimal electrical interference in the area.

Note: Inaccurate tests are caused by: 1) The presence of electrical interference 2) Any metal object within 2 feet of the search coil (hardware in the bench or table, or watches, rings, etc. on your person) 3) Improper ground balancing (this test should be done in the fixed ground balance mode or properly manually ground balanced to a ferrite ring)

Similar procedures are typically used by most manufacturers to determine the health and performance potential of the detector.

Troy