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CliveHamy

Improving Depth Detection Tips

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I would like to understand how Depth Detection works with the Nox (I assume same for other detectors) and discover tips for improving depth detection. I've only been detecting for 1 year, using a Garrett ACE 150 with a dig-it-all attitude essential for beginners. I've now moved to the awesome Nox 800 and want to be more discriminatory in my digging. The Ace depth detector always gave a reliable indication of depth, each spade accurate to 2". I'm not so sure about the NOX, it may be that because it is detecting at such great depth (I'm finding down to at least 15")  that more items seem to be >8" or maybe this is a weakness? Anyway it is a brilliant machine, by far the best choice for someone like me moving from beginner. 

So a) what is the physics behind depth detection?. (timelag measurement?, phase change?)

b) what tips for deducing depth? (I've picked up on the triple tone for items very close to the surface, is when the nox shows 5 spades and the item is 6"down I find annoying)

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Depth meters on metal detectors are nothing more than a signal strength indicator calibrated to a certain size target. A lot of U.S. detectors are calibrated to a dime size target. As the dime gets deeper, the signal gets weaker, and the meter reflects this weakening signal strength.

Detectors designed for gold prospecting only never have depth meters, because they are useless when hunting naturally occurring objects with infinite sizes and shapes.

Items smaller or larger than that dime will not read accurately. Small targets with a weak signal will read deep but be shallow. Large items can read shallow but be deep. Even the dime will not read accurately if at an angle or on edge.

With rare exceptions changing coil size or type completely invalidates the depth reading accuracy. The White’s V3i lets you enter the coil used to compensate. Other detectors use “smart coils” with an embedded chip that tells the detector which coil is hooked up, so the machine can compensate.

Highly mineralized ground and adjacent targets can also skew depth reading meters.

Add that all up, and frankly I don’t pay much attention to depth meters, especially since I often detect for items other than coins. In my simplistic world deep items are fainter and have softer edges to the audio response. Shallow targets have louder, sharp edged responses.

Equinox maintains full signal strength on coins to several inches instead of getting weaker from the very first inch. This means the machine cannot use the signal getting weaker in that first few inches to gauge depth. The signal does not drop off for several inches. Because of this, in my mind at least I call coins as either being deep or “not deep”. I can usually call deep coins very accurately based purely on the sound, which to my ear has a nice mellow response. Coins under 4” all tend to just bang out as if they are near surface, and it’s only the coil tending to give multiple responses on the shallowest coins that adds another dimension of the “surface coin” at less than an inch.

It is the Equinox pinpoint function that really tells me more about target size and depth than the depth meter. Shallow targets are initially really loud/squeaky, deeper target much fainter. Pinpointing in conjunction with lifting the coil can both size and identify large items like sprinkler heads and beer cans.

A good simple handheld pinpointer is a great device also. If you can hit the coin type target from the surface with a handheld pinpointer, it’s shallow. If not, it’s deep.

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Thanks again Steve, several great new insights, the key being that signal strength received is used as the main depth indicator. Does that mean if you discriminate out certain tones/ID's then you may be reducing the overall signal strength received, and then the depth Indicator may show shallower than if in All Mode? - Apologies if the question is irrelevant - You've made it clear you use other techniques to judge depth.  

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Anything that affects the signal strength directly affects the depth reading. Depth meters on detectors are mostly a gimmick. They really only apply to coin detecting. If you have a detector with a good, modulated depth meter, it helps a person focus on just digging deeper coins, which in theory will be the older ones.

Assuming a detector is calibrated to a dime, and you get a dime reading at 6", if you are at 8" and still digging - it can't be a dime. It is a deeper, larger item that is tricking the meter. So give the hole up and move on.

So a good depth meter can be an aid when coin hunting for sure. Outside of that however they are superfluous to most detecting tasks.

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The Nox, IMO, doesnt have quit the information that say the CTX does that will allow you to know more about the target.   If you have a detector with good TID.... or modulated tones you can gather way more information than using a depth meter.   Like Steve said...... if you know its a dime and its not there........ more than likely its not a dime.

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