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E.. Problem Common Trash; so-called 'False Signals'; Useful Search Techniques.

May 11, 2021 06:26AM avatar
Problem Common Trash:

If you are just starting out in this great hobby, you'll find out soon, if not already, that the crimp-on, crown-type Bottle Caps are one of those very pesky items. If you have been detecting for many years you'll know Bottle Caps are troubling..But if you have followed my series of Posts starting with 'A', then you'll we we didn't have a lot of problems in those earliest days with the detectors we used.

Another similar-shape problem object that Relic Hunters tend to encounter more frequently than urban Coin Hunters are round washers. Those round, often rusty, Iron Washers of various sizes can 'misbehave' like the Bottle Caps. A man-made object that can give us fits by producing a high numeric VDI read-out similar to a Penny, Dime or Quarter, with an accompanying Tone ID, if your detector has that.

All detecting activities, urban or remote, Coins or Relics, are going to present us with Bottle Caps and similar trash targets that, unfortunately, often 'sound good'. There are ways to deal with the issue by simply learning some techniques. They are useful, easy-to-employ, and all we need to do is appreciate why we have some differences in performance based on the circuitry design, and also on the search coil type. Double-D coils tend to not handle a lot of trash as well, but most manufacturers have shifted away from a functional Concentric coil, sadly, and it's now up to us to make the best of the site environment because the circuitry or coil can't. Or at least not as well.

so-called 'False Signals':

We might ask, just what is a "False Signal?' It can be a tough question to answer because some examples, or most examples, could be argued. For example, if you sweep over a US Indian Head Cent or an early Wheat-back Cent prior to about 1920, and you get a visual response with a VDI read-out and audio Tone ID suggesting it is a modern Zinc Cent, would that be a 'False Signal'? They were made out of 95% copper and 5% tin and zinc like the other Lincoln Cents that followed, but they produce a lower response like a lesser-conductive Zinc coin.

How about the modern Pry-Tabs that usually have a VDI response very similar to the US 5¢ coin range. I have a same-looking Pry-Tab found at a park picnic area that responds almost exactly like a more-conductive US Zinc Cent. Is that, therefore, a 'False Signal'?

I often hear or read about people who have a noisy detector from EMI, but they describe that as 'False Signals'. I guess, to them, it is. Beeping audio when nothing is being swept over, so they call that a 'False Signal'.

Then there are the times when we increase the Discrimination level to reject unwanted lower-conductive targets, but still get a 'Beep' from something we thought ought-to-be rejected. Are those 'False Signals'? I believe this is one of the issues we have that might qualify as a 'False Signal'. And one of the best examples might be the crimp-on 'Bottle Cap'. A round, rusty washer also fits that category because both of those objects just might produce a good-sounding higher-tone and worthy-target VDI.

But why? How about all those Iron Nails our early detectors simply ignored, but today we have people complaining about a lot of them producing a good audio / visual response? Why? In this and similar cases, I'll suggest five reasons:

One.. We are referring to Iron / Ferrous-based metals.

Two.. They are also a man-made or man-shaped object .... and that can make a difference in conductivity.

Three.. The Iron objects orientation to the search coil.

Four.. The metal detector's circuitry design.

Five.. The search coil type as well as size and shape.

Let's discuss Two for a moment, referring to "Man-Shaped". This is an example I have used in club or group presentations, my seminars, or when I had a shop as a dealer. It is a simple way to demonstrate several things, and in this case we'll use it as an example for this topic. You will need your detector with a practical search coil for hunting in trashier sites, and then find one (1) old-fashioned Paperclip. Not a modern plastic type, or a metal one that is painted or coated. Just a bare-metal Paperclip that is Iron, and you can check to see that it sticks-to / is attracted-to a magnet.

Then follow these steps as it becomes 'Man-Shaped' and you check it with your detector. Have the Discrimination set at '0' or at its lowest Disc. setting. Now, follow these steps:

#1.. Open the Paperclip so it is a straight piece of Iron metal. Place it on the ground and sweep across it lengthwise and cross-wise and note the audio response and a VDI read-out.

#2.. Next, bend that straight Irn wire to form a 90° angle. Again, place it on the ground and sweep the center-axis of the coi across it from any angle. Note the audio response and visual VDI read-out.

#3.. Now let's straighten the Paperclip out again, but bent a small 'hook' or 'U' shape at each end of the straightened Iron wire. Sweep over it again and listen and look at the target response.

→→→ Learning anything yet? ←←←

Okay, just two more 'tests.' using one single Paperclip.

#4.. Bend the straightened Paperclip to form a 'U' shape and place that on the ground. Sweep across it from the sides, the bottom or the open end and note both audio and visual responses. Is it producing a good low-tone, Iron Audio sound and a lower Iron range VDI read-out?

#5.. The last thing to do is now bend the Paperclip around to form an 'O' and hook those two 'hook' ends together so they are making good contact. Same single Iron paperclip. Place it on the ground and, once again, sweep across this now 'Man-Shaped' piece of Iron. Note the audio response and visual VDI read-out.

Any difference? You didn't change the detector or settings or search coil so you can't blame them. You didn't use a different test piece, only the same magnetic Paperclip so it isn't the Paperclip's fault. It was simply YOUR fault for taking a piece of Man-Made Iron and then 'Man-Shape' it such that it is now a problem target to deal with. So, it's YOUR fault. The target object's metal make-up didn't change, but due to the new shape the effects it has on the EMF is different because it now has an enhanced conductivity simply due to its shape, as well as the orientation to the coil.

Leave it in the new connected 'O' shape but stand it 'on-end' and sweep across it from different directions with the center-axis of the coil and note the responses. Interesting, isn't it? Now, wouldn't you say that might qualify as a 'False Signal'? I wouldn't, and in a bit I'll explain why.

Let's continue. Now that you learned how YOU can mess up a a bad-target and make it appear to be a good-target, let's correct that situation so that YOU can now 'classify' a probable Iron-based piece of trash. Even the ones that Man-Made and Shaped that give you fits.

Useful Search Techniques:

We are not through with this new, enhanced conductivity Paperclip yet. Just hang onto it for a few minutes.

Grab a newer crimp-on Bottle Cap as well and older flattened-out Bottle Cap. We are going to take these 'test samples' along with the 'O'-shaped Iron Paperclip to a metal-free patch of ground. Once again, we will have your detector settings with the Discrimination at 'O' or the lowest allowable setting. If your detector has automated or manual Ground Balance, you will do so over that metal-free patch of ground so we can rule out any ground mineral related issues.

► But first, a quick look at another long-used technique that I named ... 'Edge-Pass Rejection'. or simply 'EPR'.

There were actually two 'techniques' I named, and both were used to help 'classify' probable ferrous trash. The first, 'EPR' was something I started using by the mid-'70s with Threshold-based Discriminators, and I've used it and instructed this technique right up to the present with our modern equipment. The other 'technique' I named 'Quick-Out !, which I also still use in some locations based on the density of trash. I started using this 'technique' in '83 when we got the good slow-motion Discriminators, and it works best with those 2-Filter circuitry but can with some of the 3-Filter and other newer detector designs that are also engineered to work well with a slow sweep speed.

Remember when in the earlier posts I related how it was easy to audibly 'classify' a lot of ferrous junk with those TR and TR-Disc. detectors we had? That was simply due to the natural ability of a Metal / Mineral Locator, aka metal detector, to produce an increased loudness for a Non-Ferrous target, while most Ferrous objects would cause the Threshold audio to null-out or go silent.

As detector designs moved along and we got Discrimination, and then moved to the VLF range with VLF / TR-Disc. models, most had a higher Disc. level at the minimum setting than we enjoyed with the conventional TR's. That meant lower-conductive good target loss, but we also started to experience some issues with Bottle Caps. Some models would produce a 'Beep' when they could have been ignored / rejected as a 'mineral' or 'ferrous-based' object. That was in the mid-'70s, and then when we moved on to the VLF-Disc. or fast-motion type Discriminators from '78 on, those blasted Bottle Caps created even more of a challenge because they would often sound like a good target. And that was before we had visual Target ID. It was audio, only, until 1983 to the present.

For me, it wasn't a problem because I was still devoting 85% of my avid detecting time to Coin & Jewelry sites that did include all the routine urban locations as well as vacant lots and renovation work where I did encounter more ferrous debris. Some was easily dealt with by the circuitry design, but Bottle Caps, with some models, started to present some problems with readings above where the Discrimination was set, and that was usually enough to knock out Iron Nails. No problem, I just used my 'EPR' technique and that quickly 'classified' most Iron trash so I didn't have to make any recoveries. I just kept hunting for the better stuff.smiling smiley

Okay, Okay ... I'll explain E.P.R.. Once we started getting favorable audio responses from ferrous objects that should have been ignored or Discriminated like they used to be, I knew it had to have something to do with the effects of those Man-Made objects on the EMF (Electro-Magnetic Field) and remembered that from the earlier days, I could hear the effects of an Iron object away from the search coil's EMF farther than the response from a non-ferrous object. That confirmed the fact that Iron had a greater affect on the EMF than Non-Iron. Thus, there must be something going on at the outer-portion of the EMF that could help qualify (classify) the type of metal of the object.

I had a Bottle Cap on the ground near where I located a non-ferrous coin, so I swept over the coin directly with the center-axis of the coil and heard the loud audio response. Then, slowly, I swept the coil back-and-forth across the coin while slowly drawing the coil back towards me. The audio started to get weaker from the coin until I was just in slightly toward the center of the coil, but was still hearing a solid 'Beep' until I reached the point where there was no positive response and I was back near a proper Threshold audio. That was with the earlier detectors that relied on a slight audio Threshold 'hum'.

Then I swept over the nearby Bottle Cap with a direct-approach sweep and got a positive audio response, or, depending on the VLF / TR-Disc. and settings there was sort-of a positive response. So I then swept the 'edge' or the coil past the Bottle Cap, actually about ±1" in towards the center with most coils, and, listening to the Threshold Audio 'hum', I could hear it null out and go silent. The non-ferrous coin didn't do that, but the Iron-based target did. That gave me an audio indication that I could 'classify' that target as probable Iron and simply ignore recovering it.

Brief comment about 1983. As mentioned, we got the slow-motion detectors with quick-response and fast-recovery as well as the introduction of visual Target ID. I used the latter, but not near as much as I used those slow-motion Tesoro's. However, once we had visual and audio Tone ID incorporated in a good-working, slow-motion detector, things changed. I could benefit from the slow-sweep with quick-response AND make use of the visual Target ID and Tone ID ... for searching in dense iron-contaminated Relic Hunting sites.

Not for the use of, and to put a lot of trust in, the numeric VDI read-out to identify coins correctly, because while they might in an ideal encounter, they seldom will in dense trash due to partial target-masking and / or the blended visual and audio report of two or more non-ferrous targets together, such as a Nickel and Dime, etc. Even though I still,enjoy my non-display Tesoro models for any urban or remote-site hunting, I have my favorites from today's 'modern' digital detectors with VDI & Tone ID.

Why? Because they have a very good, broad-range of Discrimination adjustment, numeric VDI read-out, and Tone ID which allows me to adjust the Discrimination to 'accept' ALL metal targets, ferrous and non-ferrous. I can also set the Discrimination to just barely 'reject' most Iron Nails if things really get annoying, or, my preference, set the Discriminate level to a point just barely below most Iron Nails so that I 'accept' them as well as the more conductive Iron, but still enjoy the visual and Low Iron-audio Tone ID.

In some cases we do encounter problem Iron junk, b it a Nail or Bottle Cap or rusty Washer, etc., that can give us a broken good-audio response or a very clean-sounding audio like a higher-conductive US coin or trade token or gold or silver jewelry or button and - - - -., and the area is quite littered to the point we can not off-sweep the object to check it out using EPR, and when that occurs with many of our newer detectors, I do employ 'Quick-Out!'

Due to the fact that most current-era detector circuity provides us with slow-motion sweep speed as well as a quick-response / fast-recovery processing (some obviously working better than others). a lot of the unwanted ferrous junk that gives us questionable or better audio response can be made to break-up or give a proper Low-Tone Iron-Audio sound and visual low numeric VDI with a very 'Quick!', but very short-length sweep directly across it and the response might kick 'Out' the trash response. Does it always work? No, but 'Quick-Out!' does help out when there is not much room to sweep the coil off-center of the located target.

My min-use 'technique' to quickly check and classify problem Iron trash is to rely on 'EPR' and, once centered, I work the coil back-and-forth as I pull the coil closer to me and near the outer edge of the coil, or I might advance the coil on the side-to-side sweep forwards and away from me to get close to the rear-edge. If you use an annoying Bottle Cap you will see that while it can give a good audio response on a direct sweep, using EPR will allow it to be properly 'classified' by audio and visual response.

Was that Bottle Cap making a 'False Signal', or was it the Detector or the Coil or the Settings? As I described above, there are different factors, but the main one is that it was a Man-Shaped problem-target. In a clean area lay a Dime and Quarter and Bottle Cap and that 'O'-shaped Paper Clip on the ground, in order, one at a time. Sweep directly across the non-ferrous coins and note the Target ID and Tone ID. Then use 'EPR' and off-sweep with the coin ± an inch or so from the coil's outer edge and working the search coil at a functional 2" height. It tells you it's probably a good target and doesn't tell you anything else using the Dime or Quarter.

Use the Bottle Cap and note that with 'EPR' you are going to get a change in the target response and now have a Low-Tone audio and low-reading VDI of an Iron target, so it now 'classifies' that as likely trash. Now it's time to put that 'O'-shaped Paper Clip on the ground and do the same thing. A direct sweep produces a higher visual and audio read-out that is not a 'proper' identity of what you just encountered. But that, as we noted earlier, was YOUR FAULT because YOU took an Iron metal object and Man-Shaped it into a higher-conductive object that also effected the EMF 'differently' ... but NOW you can properly classify it. Use 'EPR' and it will now let you know you fooled yourself because it really is an Iron trash object. 'EPR' to the rescue!

So there you go..Perhaps another lengthy post but it was meant to be helpful. To get everyone up-to-speed with some of the day-to-day annoyances we might face, and learn how to take them on. There's no magic solution for Bottle Cap Rejection today, that I know of, that works as well as some of what we have had in the past. I had BCR on my White's Pro XL and XLT and it kind of worked OK, and helped those 4-filter, fast-motion detectors with some problem Iron.

But as we moved into more of the analog/digital to just digital circuitry with comfortable slow-motion detectors, the challenges of some man-made Iron increase and it has been up to us to learn how to handle it. Now you know and just need to spend a little time with each of your detectors to learn how it might help, and see how well these techniques can work for you and places you hunt.

Just a reminder here. Most Bottle Caps are going to be found on the surface, or typically no more than surface to about 3"-4", and at those depth ranges EPR can usually work well. Sometimes a little deeper, depending on the detector and the search coil size and type. The same holds tue with rusty washers and other man-made ferrous trash, but as the coil-to-target distance increases, the intensity and size of the EMF is different and some problem just won't be able to be classified.. Iron Nails can be an issue , too, due to any bends and angles they have, their orientation, and the 90° position of a nail head. Still, I've been using 'EPR' techniques for over forty-five years and it has helped me deal with heavily-littered challenges to eliminate recovering worthless trash.

Could I have missed some good targets doing so? Certainly, but I have used 'EPR' in my favor quite often, especially on one-time hunt opportunities. When I worked for Compass Electronics and was using their new Scanner XP Pro prototype in '88, which was the first VDI model I enjoyed using with Target ID, our metal detecting club had one-day permission to hunt an out-of-use old picnic grove. It had seen heavy use in its hey-day but was only an old site with a likely abundance of discarded Bottle Caps as most use was from earlier and long before canned beverages and Pull-Tabs.

But that also meant it was site with a fair amount of older-coin potential. and we only had one day to find all we could. I wanted to check out how well the Scanner with it's segmented needle meter worked for Target ID and to classify those Bottle Caps. I started my search and would get the assortment of audio responses from whatever was there, and on two suspicious targets I used 'EPR'. They sounded like Bole Cps and the 'EPR' technique suggested they might be with the low-Iron read-out when I checked. I recovered those two just to confirm I was properly identifying or 'classifying' likely Bottle Caps, which they were, and decided I was done digging them. I hunted on finding coins and other non-ferrous targets, but checking suspicious targets with the off-centered sweeps to confirm Iron junk.

Two members, sing their different White's TID models were watching me and curious about the new model that was coming out. They saw me pause, make a few extra sweeps of a pin-pointed target, and then moving on. They then moved in, located the target and recovered it .... them. After about half-an-hour of finding coins and keepers, but no more than those first two Bottle Caps, they approached me and told me I was finding and leaving a lot of targets behind. I said: "I know, they were Bottle Caps so I left them for you two."

Thy asked,: "How did you know?" I looked down t the prototype and said: "Oh, I'm making use of 'EPR." They said: "Oh." and on I wend detecting. maybe fifteen minutes later they approached me again, after recovering a few more Bottle Caps I wandered away from, and pointed at my Scanner and asked: "What is EPR?" I chuckled a little and told them it wasn't any sort of new circuitry feature and had nothing to do with the new detector. It was simply a 'search technique' I use to help classify likely Iron trash such as Bottle Caps, and their detectors could do it also. The I asked them to place a Bottle Cap on the ground, since they had a lot in their pouches, and I demonstrated 'EPR' to them with my Scanner XP Pro and then their two different White's models.

We all went on doing what we could to pluck keepers out of that old picnic grove, and they only recovered a couple more bottle caps that were foolers, and I think part of that was due to their search coil size and the 4-Filter / fast-sweep designs they were using. Thus they did enjoy the learning and future hunting experience.

Learn what you have, employ all the patience you can, hunt slowly-and-methodically, and all the best to you in those old-use / Iron-challenged sites.


"Your EYES ... the only 100% accurate form of Discrimination!"

Stinkwater Wells Trading Post
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Subject Author Views Posted

Now we are going to take a stroll out of the urban trash.

Monte 287 May 06, 2021 10:46AM

F.. We have now arrived at Iron Nails and Rusty Tin ... What to Use and What to Do?confused smiley

Monte 104 May 14, 2021 02:37AM

E.. Problem Common Trash; so-called 'False Signals'; Useful Search Techniques.

Monte 122 May 11, 2021 06:26AM

D.... The next major advancement: VLF-Disc. and Motion-Discrimination.

Monte 102 May 09, 2021 09:22AM

C.. And then came the Discriminators, and VLF's and VLF/TR-Disc.

Monte 80 May 07, 2021 06:27PM

B.. Just what was a "Metal / Mineral Locator" I spoke about?

Monte 88 May 07, 2021 10:03AM

A.. First, let's follow the path that leads us into various Iron / Ferrous debris.

Monte 158 May 07, 2021 05:08AM

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