Metal Detector Discrimination Really Sucks

[Steve Herschbach]

I am primarily a prospector but have also been coin and jewelry detecting since 1972. Like most people when in parks I use discrimination to pick targets but when prospecting I usually dig it all. Not always though, sometimes I am tired or an area is just too trashy so I crank in a little VLF discrimination to sort things out.

The problem is when prospecting I have seen some pretty scary things. It is one thing to walk away from a dime because your detector called it a nail. Think about walking away from a solid multi ounce chunk of gold because your detector called it a nail. Not likely, you say? Far too likely, I am afraid. I and others dig big nuggets other people leave behind on a regular basis, and I know I have missed some very big ones myself in the past. It gets your attention to realize you may have walked away from $40,000.00.

I have this pile of detectors headed my way to check out. One, the Nokta Fors Gold, showed up yesterday. Good first impression out of the box, but that is another story. The main thing is today I got it out along with a Gold Bug 2, Gold Bug Pro, F75, White's GMT, and CTX 3030. I rounded up a 1 gram gold nugget and a collection of nails and hot rocks and did a little playing around this afternoon.

I am still waiting for the XP Deus to show up and a V3i so this was more about coming up with some methodology more than anything. My interests run more towards hot rocks and magnetite sand than would be the case with most people. So the particulars do not matter at the moment, except this.

Discrimination sucks! You fire these babies up in all metal and they are all powerful detectors that do the job, with some amazing depth for VLF units (not counting the CTX which lacks a true all metal mode). It is pretty easy to compare units as it really just boils down to depth and how well they handle hot rocks, which is mostly a function of frequency and ground balance. EMI is a big factor in urban areas also but much less so when prospecting.

So then I put the detectors in disc mode and I just cut the legs out from under them. Bam, instant lost depth. Also, target masking or so-called reactivity is usually a non-issue in pure all metal modes. Not so at all in disc modes, and disc modes that lack true zero discrimination settings mask targets immediately even when set to zero.

Anyway, all I can say is playing around for awhile with these units and my pile of hot rocks and little nails was rather disheartening. It was just so darn easy to get that little nugget to bang out loud in all metal, then disappear entirely in disc modes. Or get detected but called ferrous. Or get masked by a nearby hot rock or nail. It just hammered home with me once again the huge difference in raw power between something like a GPX 5000 and even the best VLF detectors in all metal mode, and how that huge difference becomes an almost impossibly large gulf once you turn to disc modes. When you just go detecting in a park you do not see what you are missing. But in my case it was all to visible and really kind of bummed me out seeing just how far we have to go when it comes to metal detector discrimination.

The only icing on this cake is that there is a huge amount of fantastic stuff in the ground, and not deep at all. It is there, quite shallow, just under or near that thing you discriminated out. If we could see through discriminated items rather than be blocked by them an amazing amount of stuff would come to light.

Beneath The Mask by Thomas Dankowski

The Painful Truth by Thomas Dankowski

More Reasons Discrimination Sucks by Steve Herschbach

[deathray]

Very good and important write up Steve. Looking forward to your results with the Deus.

[Northeast]

Hi Steve.  I'm slowly making my way through the links you put up to my other question.  They have all been interesting and I am learning!! 

So, your thoughts above were disheartening for you. Has that ALL changed with the Equinox or is it just a decent step in the right direction?  

Thanks 

[Steve Herschbach]

All VLF detectors suffer the same problem when trying to employ discrimination. In simple terms it is a target signal to ground signal ratio thing. You want to find a tiny item in the middle of a large volume of ground the detector is seeing. The ground reads ferrous and the desired target non-ferrous. In bad ground, it is easy for the ground signal to overwhelm the target signal causing it to be detected but to read ferrous.

All Equinox does is improve on that situation, but it only does so by pushing the depth at which these changes occur back a little further. But if the target is deep enough, or the ground bad enough, Equinox can still make a wrong call. This is the number one reason I prefer to hunt with tones identifying ferrous items instead of blocking out ferrous items entirely.

An old tip from my White's MXT page (edited)...

"There are four things to know. 1. Target ID numbers increase as the nugget size increases. So a 1/4 oz nugget may read around 25 whereas a 1 oz nugget may read around 40 and a 2 oz nugget may read around 50 on the meter. 2. The larger a nugget, the deeper you can detect it. 3. Certain steel items can give positive target ID numbers and 4. Target id numbers are pulled down the deeper the nugget is buried. A 1/4 oz nugget near the surface will read 25, but at depth might read 10, and at max depth may finally read at 0 or lower and actually be identified as iron.

This last point is very important, for if you run a Fisher Gold Bug 2, or Tesoro Lobo, or Troy X5 in disc mode to tune out iron, as is common, deep nuggets may read as iron. If they are, the machines will reject them; you will get no signal, and walk past the nugget. You will never know it is there. Or at best you have to search in all metal mode, then constantly switch to the discriminate mode to check the target. With the MXT employing tones to separate ferrous from non-ferrous, there is no switching and you hunt completely by ear.

With the MXT I like to run the detector in relic mode, with the disc set precisely at 2. Non-ferrous items will give a high tone, and ferrous junk a low tone. If you get a faint low tone, the first thing you do is kick and inch or two off the surface until you get a honk or a chirp. Now dig a little deeper. If the VDI number rises, keep digging. Targets that read iron initially and rise will often turn into non-ferrous readings, hopefully gold. If the VDI number stays the same or goes even lower, you have an iron target."

[DSMITH]

I started using 0 discrimination with the XTERRA 705 while living in Ohio I always felt when in 0 discrimination and prospecting mode I gained quite a bit of depth with the 705 I also would run with 4 tones or 2 tone when I would run in coin mode I always had a feeling that when you ran in the 99 tones the 705 also lost depth but I don't know if that is true or just my own thoughts and the 99 tones always drove me nuts so I would always end up switching back to 2 or 4 tones,one thing that convinced me to run with 0 discrim was while in my back yard in Ohio I had went over an area next to a big oak tree with discrim and 99 tones set and was getting no signals what so ever so I stopped and set discrim to zero and went to 4 tones re scanned the same area again around the tree and ended up getting a signal which ended up being a 1941 merc down about 10 inches so since then I always run with zero discrim and 2 or 4 tones set    

[Steve Herschbach]

Thanks phrunt, I am glad the information is helping people.

On 1/3/2018 at 3:45 AM, Northeast said:

So, your thoughts above were disheartening for you. Has that ALL changed with the Equinox or is it just a decent step in the right direction?  

Thanks 

Sorry, I missed this bit earlier. No, Equinox changes nothing. The issues appear to be inherent in the basic technology itself. There are clearly good targets, clearly bad targets... and then the mess in the middle where everything overlaps. No matter how you slice it, discrimination is unreliable at best, and robs machines of significant depth.

Yet I use discrimination quite often!  The trick is understanding the trades that are made when doing so.