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Rambling a bit about: Ground Balance ... Target ID ... Search Coils.

November 07, 2020 11:42AM avatar
I've related this story a few times here or there, but it 'fits' so here I go again.

Ground Balance and Search Mode Effects:

It's late 1987 or very early '88 and I was the Marketing Director & Dealer Coordinator at Compass Electronics in Forest Grove, Oregon. They were trying to push production of the new, just released Scanner XP Pro, but still had some sample/test units out for review and input. My office was in the lobby right next to Ron Mack, the company President, and he had a call from an experienced fellow in Alabama, I believe. He talked with him a while, and I could hear him explain that half-dollars were not out there in abundance to be found. The guy called maybe three times and Ron stepped around the corner to my doorway and told me this guy was driving him nuts with phones calls about how the XP Pro wasn't finding silver coins. He asked if I'd take the next call from the guy and set him straight.

The guy called the next day and I was away from my desk back in the shop and Penny directed the call to Ron. I go back and hear the repeated conversation and hear Rod tell him, something like "there are not that many 50¢ pieces out there to be found." I asked Ron to ask the caller: "Is it that he can't find them, or that they are not responding in a test?'

I heard the answer, turned around and headed back to the Shipping Department and asked Myrna to stop boxing the XP Pro on the carts that were sent down. I rolled the cart to a table and pulled 10 XP Pro's with their coils off the rack to check them. I was ready because almost all the time, from about 1961 until a seminar around 2003 or so, I carried a Morgan Silver Dollar in my pocket. I always liked them, and still do, naturally, and in the early '60s when I took my lawn-mowing or berry-picking money to the bank, I'd always get a Silver Dollar in change before I left. I liked them and carried one sort of for 'Good Luck.'

I used it, and had a 50¢ piece handy as well, and checked all th detectors that came out-of-production. I told Myrna to leave them and I'd be right back and headed to the front office, stopping to let the design engineer, John Earle, know we had a problem. I then got Ron and had him follow me and John to the table of detectors. Almost all of them would not respond to a Silver Dollar, Seven wouldn't beep on a 50¢ piece, and a couple had difficulty with a clad Quarter. I knew what the problem likely was, and John watched as I demonstrated them all and said,"I know what the problem is." Production stopped until John re-rote the calibration, aka tuning, procedures for the internally-set GB trimmer. Why? The GB was way too positive.

I explained to Ron the fellow wasn't saying he couldn't 'find' a Fifty Cent piece, he was saying the detector would't Beep or Respond to a Fifty Cent piece, and the reason was an errant GB adjustment.

Remember, that was way back 32 or 33 years ago, and 1988 was only 5 years after George Payne brought us our first visual Target ID detectors with the new Teknetics Coin Computer. Back then there were a lot of 50¢ pieces still in use and circulation, and while the big Silver Dollars were not in regular circulation, there was a few more out there to be found ... back then. Fast-forward to our modern era and we don't use, see or spend those big $1 coins, and many detectors over the past ten-to-twenty years have been designed such that the highest indicated target on the visual Display is a 50¢ piece. No $1 are shown because we don't use them thus we don't lose them.

Additionally, remember that most metal detecting Hobbyists, especially here in the US, are really just the casual, now-and-then urban Coin Hunters. They want to find coins, modern but older if they can, and thy, as a whole, do not want to hear or deal with trash. They are also not very Avid Detectorists or all that active at learning how to make adjustments, or what they are for ... especially, Ground Balance. Therefore, many detectors have been made for Coin Hunters to make it easy, and to do so, the majority of the detectors we grab today rely on a preset GB, especially for the motion-based Discriminate mode.

If the GB is too negative for the ground mineralization level, there will be falsing. Manufacturers don't want consumers complaining about falsing, so they design a lot of detectors with a preset GB in the Discriminate mode, or one controlled so as not to go too negative, Thus, by design, countless detectors are produced such that the GB is preset or controlled, but set too high in the Disc. mod. The consumer doesn't have to learn how to GB a detector, and they go hunt wherever they want and do not have to listen to and deal with false signals from a too-negative GB.

I have been using Tesoro's since July of '83, and back then I used a few of their 'turn-on-and-go' models (that means factory preset GB ) but mainly those with Manual Ground Balance. I was also a Dealer for them so I made sure I tweaked the GB on all of my units as well as those on friends or customers models. I didn't want them to false, but I also didn't want them to be calibrated too high to the point a detector wouldn't respond to a Silver Dollar. I have seen some, such as at Compass, so positive they wouldn't hit on a 50¢ piece, a few not on a 25¢ piece, and two wouldn't respond on a 10¢ piece.

It's usually the big $1 coin that causes the problem, but it can also include not hitting on a combined amount of higher-conductive coins, all together and touching, such as my Short-Stack of 5 Silver Halves on top of a Silver Dollar. Since we don't luck upon Silver Dollars as often as we used to, I can get along OK with most preset detectors. However, as I stated in the above post, I make sure I DO have some models on-hand that allow me to control the Discriminate mode's GB reference. There are times and locations where that works to my favor. I mentioned I had four models that provide operator control of GB in the Disc. mod, and one of those is my back-up / spare Tesoro Bandido II µMAX I have listed in the Classifieds.

The types of coins we generally might find are what we need to be aware of, and I pointed out some problems with detectors of the past that had a GB related issue by design. It was more important to me at the time, because from fall of '71 until the summer of '93 I had a lot of very good opportunities to search some old home-sites that dated from about 1900 to 1940, and that period included some tough times going into the Depression Era. A period when a lot of people didn't trust banks and often they would secret money around the home or property. That is one reason I have my 'Short-Stack' to replicate a Silver Coin Stash. Not a larger-size Cache, but just a smaller amount that people could Stash-away in case their pockets ran empty but they needed bread or milk or potatoes or something.

Then, too, I believe a few small coin-stashes I found were due to kids playing around and slipping coins in a slot or crack around a window. Those were mainly smaller-size coins, such as Pennies and Dimes, and I have good memories of chancing upon a dump of silver dimes that fell out when they moved one of the old houses off the foundation to relocate it. I was living in the Portland, Oregon area where it rains all too often and that worked to my advantage,

The rock and dirt driveways had numerous water puddles in low spots and that was exactly where the corner of the house passed over when moved off the foundation, dumping a good handful of silver Mercury Dimes in the puddle close beside the house. Out of site of any workers, but they 'beeped' quite well when I swept over that puddle of water. Thanks to all the water that helped to make sure they were rinsed and clean and shiny as each was removed, but it was a messy recovery for me to clean myself up. Maybe the best muddy mess I ever enjoyed, however.

Most of the 'stashes' we located were outside the houses that were removed, and the amounts were small, but usually all or mostly silver coins, especially Halves and Dollars. Thus my 'Short-Stack' for evaluation purposes. Still today I will use a big ol' Silver Dollar when I check out any detector of interest, just to be certain their engineering design or assembly calibration hasn't exceeded the limit. The productive era for Coin Hunting saw a lot of Silver Halves recovered and a fair number of Silver Dollars, and while we are far less likely to find them today, I don't want to miss out because a detector was poorly designed or because I didn't do my part in adjusting a detector's Ground Balance.

And of all the models I have on-hand, all of mine and the new models I bought for the evaluation, I checked every one of them using a lonely 1900 Morgan Silver Dollar and, as expected, each of them gave a good, clean signal. And with the exception of the V-540 and Midi Hoard, all of the VDI readouts were a lock-on' of '95 at 5", with one model registering '93' / '94' and one showed a locked '96.' Now, to find some new location that had ld coins.thinking

Target ID ... from Then to Now:

Our earliest visual TID models, for here in the USA, showed the lower-conductive 5¢, then 1¢ and 10¢ coins were shown together using a / mark, then 25¢, 50¢ and $1 coins to depict the big, silver $1. In '82 they changed over to the modern Zinc 1¢ and TID came out in '83, with stragglers to adopt the new feature in '84 and '85. The long-minted Copper 1¢ were still in use and very abundant and I guess they hadn't realized the new Zinc 1¢ was noticeably lower-conductive.

Soon, Coin Hunters using these new-featured detectors complained that many of the 'modern' 'Pennies' were not reporting as 'Pennies' and the engineers updated to a display that showed 1¢ Zn for a Zinc Penny and 1¢ Cu for a Copper Penny. Well, that was nice, but not for the ambitious Hobbyists to wanted some older coins and didn't like the Zinc Penny because the would quickly corrode and get eaten-away and pitted. So, they started searching older-use sites while increasing the Disc. level to reject Zinc 1¢. Then the 'average' Hobbyists learned what the savvy Avid Detectorists had figured out when TID first came out, and that was that the Indian Head 1¢, and many early Wheat-Back 1¢ from about 1909 to ±1920, ALSO generally gave a lower VDI read-out similar to the modern Zinc 1¢ !! They were shown to be made out of the same copper and alloy mix as the latter Copper 1¢ coins, but the problem was the quality or purity of the copper ore used and the processing to make it resulted in lower-conductive metal.

Then we move on to today and we still see some models that have a 1¢ Zn and a higher-reading 1¢ Cu/10¢ display, while others show the lower-reading modern coin as 1¢, or as 1¢ Zn, or simply a word Zinc, and the higher-reading coin is shown as a 10¢. It's been 38 years since we switched to the Zinc's, phased out the Copper's, and since they are not a common mintage nor as frequently carrier, detector makers zapped the Copper 1¢ from a lot of models.

Of course new TID problems crept in down in the 5¢ coin range. Those old Ring-Pull Tabs usually registers in a spread of range above a 5¢ coin, but today and in recent years there are all those rectangular Pry-Tabs (that are supposed to stay on the beverage can) that get tossed aside, and a bulk of those pests fall right there in the 5¢ range.sad smiley

Visual Target ID can be a useful tool .... sometimes, and can be fun to use .... when it works. But so often I see people out hunting with a TID model and note that they can waste a lot of time due to Target ID, and often get frustrated with Target ID, and quite often walk away from a good or potentially good targets due to TID. In the good days detecting was pretty simple:

#1.. Turn the detector On.

#2.. Tune to a proper Threshold hum.

#3.. Sweep the coil.

#4. 'Beep!' and recover the target, the get back to finding more stuff.

Today, there is often more control-fiddling, and then on to #3, the search. But when you get to #4, things change. Most Hobbyists will immediately look at the display. Not a glance, but a dedicated stare to check every display option like a numeric VDI read-out, the indicated possible target, confidence bars, Fe3O4 ground conditions, and possible depth.

Then they get back to sweeping the coil, left-and-right, faster-and-slower, short wiggles, turn partly around the target and continue with the sweeping-and-beeping over, and over, and over -----. Just trying to make their detector give them a highly accurate 'Lock-On' response, and if it doesn't lock-on solid after all that messing around, off they go, looking for some other chunk of inquisitive metal. Long, long ago I pointed out the best form of Discrimination that never fails to let you know if a target is good or bad.. See below at the top of my Signature as I made that statement and have used my quote for decades.

TID is handy to give you a quick idea of what you might be looking for in your recovery. It's also a useful tool if you have a situation such as a permission for private property that is well groomed and you want to be more selective in your recovery efforts and try to single them out for potential coins. Maybe you have a one-time access to a place you're travelling through, or a budgeted amount of time before dinner or something. Then it is a useful tool. Work a highly littered place, such as a very trashy ghost town or similar site, and visual TID is seldom going to be useful. Most of the time I am simply going by audio response because TID will be too jumpy and erratic due to so many closely-positioned pieces of junk.

So this is just a reminder to learn and understand the visual TID of your models, know the strong and weak points, and know when to and how to use it .... but never put 100% faith in it. It will often fool you. And don't find fault with a detector circuitry design just because you have a jumpy, unstable display. There can be another reason → → Keep reading.

Search Coils -- Their Size, Shape and Internal Design:

There are some basic things to know about most of the search coils used by the majority of Hobbyists and Avid Detectorists using the many VLF Discriminating detectors. Some key notes are:

TYPE: Most search coils will be Concentric design or a Double-D design. I sometimes wad a post or statement by someone saying their normal, popular Coin Hunting detector uses a Mono coil. Wrong. Mono means One and those are what work on a PI or Pulse Induction detector. Not a Transmit / Receive like most of us grab.

SEARCH COIL MATCH-UP: Just because a search coil connector fits a detector, doesn't mean they are supposed to work together. Just because two detectors operate at the same frequency doesn't mean they are going to share search coils. Just because a coil is from one brand or manufacturer doesn't mean it will fit or work on others of the same brand or manufacturer. I can't tell you how many times through the years I hear about someone wanting to try somebody elses search coil on their completely different make, model, frequency detector. It doesn't work.

COIL TYPE APPLICATION and PERFORMANCE:I also hear comments made, especially in more recent years, as kind of a blanket statement that is supposed to be 100% correct, but it isn't. One is that a Double-D coil is the best choice for use in highly mineralized ground. On some detectors and if the right size and shape they might be helpful, but I have often matched or out-performed a DD coil using a Concentric coil in some very challenging conditions. It really gets down to the size, shape and design of the specific search coil, combined with how well a particular make or model was designed to work and sometimes the operating frequency can play a role in that.

Other things to consider is that if two search coils are of the same or very similar size, a Concentric coil will usually get slightly better depth-of-detection, and a Concentric coil generally produces a tighter Target ID, thus a tighter or narrower spread in the VDI numeric read-out. That is because they have a much more consistent or uniform EMF going all around the outer Transmit winding. That also means the reverse is true on ID consistency.

The Double-D coil (sometimes also referred to as a 'Wide-Scan') uses opposing Transmit and Receive windings so as the coil is swept from the left and then from the right, the different coil will be engaging the target than the other direction. To add to that, the overlapped Tx and Rx windings are the working portion, but also influenced by the remaining outer portions of the coil. The result is a non-uniform EMF with both approaches, thus more inconsistency. Since the popular trend the last several years has been to offer new detectors with a DD coil rather than a Concentric, the result is a more jumpy of inconsistent display read-out, so the erratic behavior blame goes to the search coil in use.

Hey, it's starting to get colder and we have shorter daylight hours now, so maybe a few comments made here will help some of us give more thought to our detectors of choice and get to know them better. We can do that even when stuck indoors and away from the cold outside.


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

Stinkwater Wells Trading Post
Metal Detector Evaluations and Product Reviews
I'm now located in Clyde, Texas
monte@ahrps.org ... or ... monte@stinkwaterwells.com
Detector Outfit: A selection of my favorite makes and models, with the best coils mounted for the tasks I'll take on.
Apex .. FORS CoRe .. FORS Relic .. Impact .. Inca .. Bandido II µMAX .. Silver Sabre µMAX .. MX-5
Pinpointers: Pulse-Dive Pointer and AT Pro-Pointer .. Headphones: 'Hornet' & 'Wasp' .. MS-3 Z-Lynk
*** All working well today to make memories for tomorrow. ***
Subject Author Views Posted

Some fun evaluations of 10 Brand New Detectors you can buy for $550 or Less.

Monte 538 November 01, 2020 07:56AM

#4→→ The Compass Coin Hustler and why the '42' Point high score?

Monte 258 November 05, 2020 04:55AM

Re: #4→→ The Compass Coin Hustler and why the '42' Point high score?

D&P-OR 221 November 05, 2020 10:50AM

#3→→ GROUND BALANCE --- Some can be, some can't. ... Another Lengthy Post.

Monte 283 November 04, 2020 11:03AM

Rambling a bit about: Ground Balance ... Target ID ... Search Coils.

Monte 228 November 07, 2020 11:42AM

GB, Target ID, Search Coils.

UtahRich 188 November 07, 2020 05:08PM

Re: GB, Target ID, Search Coils.

Monte 217 November 08, 2020 07:32AM

Great Post

OregonGregg 234 November 05, 2020 06:40AM

Re: #3→→ GROUND BALANCE --- Some can be, some can't. ... Another Lengthy Post.

EL NINO 212 November 05, 2020 03:36AM

'Thank You' for the kind comments. ---- I put 'SAT' on my to-do list.thumbs up N/T

Monte 199 November 05, 2020 03:50AM

Re: #3 another Lengthy Post. Great post Monte thumbs up Thanks for that informative lesson!!!!! N/T

Hombre 242 November 04, 2020 10:26PM

Randy, my pleasure. As always, I learned things myself.

Monte 196 November 05, 2020 03:47AM

#2→→ My comments on the 10 New Detector Models Tested ... Very Lengthy..

Monte 266 November 03, 2020 04:17PM

Re: Some fun evaluations of 10 Brand New Detectors you can buy for $550 or Less.

WM6 179 November 02, 2020 06:03AM

Re: Some fun evaluations of 10 Brand New Detectors you can buy for $550 or Less.

diggindeep 209 November 01, 2020 11:02AM

Back to you, Andrew.

Monte 231 November 01, 2020 02:30PM

Re: Some fun evaluations of 10 Brand New Detectors you can buy for $550 or Less.

Timbertodd 228 November 01, 2020 10:35AM

A quick reply to you 'Timbertodd.'

Monte 214 November 01, 2020 12:46PM

#1→→ Evaluation Scores w/Detectors and Coils ... plus the 100% performer.

Monte 288 November 01, 2020 09:38AM

Re: Follow-up #1.. Evaluation Scores w/Detectors and Coils

Kickindirt 206 November 02, 2020 12:31PM

Joel, an interesting guess .... but wrong. Let me comment.

Monte 242 November 02, 2020 01:37PM

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