Ground Noise Or Emi ( Electromagnetic Interference )?

[Steve Herschbach]

I was offered this tidbit from the engineers at Garrett while discussing another subject. How to determine EMI versus ground noise using the stationary noise test.

"The stationary noise test is where the coil is held totally stationary, either in the air or more typically on clean ground, and then listen for noise. If the noise persists while stationary, then it’s EMI and not ground noise. If the noise disappears while stationary and then reappears only when moving the coil, then it’s ground noise and not EMI. This is an excellent test for any operator to help determine if noise/instability is caused by ground or EMI."

If the problem is EMI then of course you would want to try a ground cancel. All ground cancel does is scan all available channels for the quietest ones. It picks the five quietest, and then double checks those five, and settles on the best one. This checking and double checking takes a bit of time so be patient. The key is to not do anything to add noise when doing a ground cancel. Getting your pick too near, or waving the detector around, anything else that adds noise, will cause the channels being checked when that noise occurs to be rejected.

Since the EMI cancel looks for and attempts to eliminate noise sources, you may want to purposefully aim the coil at a nearby EMI source or detectorist in an attempt to knock out the specific noise source. If you use a pinpointer, turn it on and place 2-3 feet from the detector while doing the EMI cancel, to tune it out for use when detecting.

If all channels are noisy, you need to do something about it. Changing coils is one of the best solutions. Small coils handle EMI better than large coils, and DD coils handle EMI better than mono coils. Reducing the sensitivity helps. Trying other modes will possibly help. In my experience the Axiom handles EMI better than most PI detectors but it is still a high gain detector and that means some area will be problematic. Just the nature of the beast I am afraid, but again, Axiom is a step up in that department.

If it is actually ground noise, some of the solutions may seem similar. See these threads for the details. Most important of course is getting a proper ground balace. See the video below for that.

Axiom Sensitivity - A Must Read For All New Owners!

Axiom Detection Modes Explained

Axiom DD Coils - A Must Read For All New Owners!