Whites TDI Classroom

Thanks too all for the sharing of experiences and knowledge. I am purchasing a TDI SL for coin and relic hunting. I would appreciate your opinions on my explanation of the Ground Balance features of the TDI. The information I am presenting is not mine but a compilation of all post on the TDI. I fully understand this is just one adjustment of the TDI and that the delay, tone selection and gain are all related.

Ground Balance Turned Off: increases depth but all targets produce a high tone. No discrimination at all.

Ground Balance Turned ON: small loss of depth, ferrous targets (iron, nails) produce a high tone and non ferrous (brass and silver) produce a low tone (generally). Bullets can fall in between based on GB setting.

Ground Balance Adjustment: With a VLF you set the GB base line based on the soil matrix, with the TDI and GB Turned On, you can adjust GB to change the base line to cause some targets to be below or above the base line causing the target to sound high (ferrous) or low (non ferrous).
More manipulation of the base line is possible with milder soil. The closer a target is to the GB baseline, where the target signal transitions, the greater the potential loss of depth.

Posted by Detectorguru
The higher the ground balance setting the more effective the machine is at eliminating signals from small iron.

Posted by Reg
Hi tone signals (smaller iron like, ferrous) will reduce in depth as the GB is advanced. Low tone signals (silver and brass non ferrous) will reduce in signal strength as the GB is reduced. Also, the opposite is true, meaning high tone signals will increase as the GB is reduced and low tone signals will increase as the GB is advanced. Keep these basic statements in mind at all times when adjusting the GB to target a specific object.

Am I understanding and explaining the features of the ground balance on the TDI?

HH
Fred



Edited 1 time(s). Last edit at 05/02/2012 11:43PM by WTnFred.

Hi Fred,

The GB (ground balance) control has taken on different functions and even though they are related should be thought of separately.

First, the GB is mainly designed to minimize the ground signal. This is done by carefully adjusting the control until the ground signal is minimized as the coil is slowly pumped up and down above the ground. This usually happens around 8 or 9 on the control depending upon the detector and the ground conditions.

Now, at the setting where the ground signal is minimal, there will be other targets that have high tones, low tones, or maybe even minimal signals. Those with minimal signals will have responses that sort of mimic the ground signal, thus their signals are minimized just like the ground signal is.

Now, one thing found out about this detector is if the GB is adjusted to a different setting, signals from different objects are minimized and (this is important) some object's signals change tones. A good example as to what happens can be observed by watching what happens to the ground signal. Reduce the GB setting and the ground signal becomes a high tone as the coil is lowered towards the ground. Raise the GB setting and the ground signal changes to a low tone as the coil is lowered. So, changing the GB can minimize the ground signal, make that ground signal change to a high tone or a low tone just by the setting.

Now, at the normal GB setting, a large piece of iron such as a larger nail will cause a low tone. Silver and copper coins dime or penny size or larger also create low tones. Smaller pieces of ferrous junk such as a small piece of an old tin can or maybe a bottle cap, or even a boot tack will usually create a high tone. Other objects that create a high tone will be small gold objects or anything else that has a decay curve that decays faster than the ground signal. Such objects are generally referred to as low conductor objects. Objects that create a low tone are commonly referred to as high conductive objects. High conductive objects create signals that last much longer than the ground signal, so their decay curve is longer than that of the ground signal.

Now, what was discovered was other objects can also change tones if the GB is adjusted. An example is the signal from a large nail. At the normal GB setting, the signal from the nail is a low tone. Reduce the GB setting slowly and you will find a setting with the signal from that same nail becomes almost minimal. Further reduce the GB and that same nail now creates a high tone. So, at a particular setting, maybe 3 or maybe 4 or so on the GB control both the ground and a nail cause a high tone response. Thus both the nail and the ground signal changed tones simply by changing the GB setting.

At this particular setting of a GB of 3 or 4, still other objects such as a silver dime or a copper penny will still generate a low tone response. So, there will be objects that remain a low tone even through most or all of the range of the GB adjustment.

On the other hand, take a nickel and the signal from that object will remain a high tone throughout the GB range. Still other objects such as small gold or other low conductor type objects such as small foil, etc, will also remain high tones.

Now, if we take this information and put it to use, we can use the GB control to simply adjust to minimize the ground signal, or we can adjust the GB control to a certain setting and then use the single tone feature set by the conductivity switch to eliminate the unwanted tone.

Lets say we want to ignore nails and the nail changes tone at a GB of 4. So, at a normal GB of 8, the nail is a low tone, but at 4 the nail is a high tone, then by switching the conductivity switch to high conductor and turning the GB down to 4, most nails will be ignored.

What is nice is the fact that at a setting of 4 or so on the GB control silver and copper coins are still low tone signals while most large iron objects are now high tone signals. So, if we select the high conductor setting, which allows low tone signals to be heard but ignores high tone signals, then we only get a response from the silver and copper coins while ignoring most iron trash.

Keep in mind that as the GB is adjusted, different objects may change tones while others may not. Knowing this plus what happens to the signals of all objects as the GB is adjusted becomes important to remember if maximum depth plus some level of discrimination is desired.

So, if we experiment with different objects, we can determine as to where they may change tones or not change. Using this information, we can then use the GB control to sort of tell us what an object might or might not be. We must also keep in mind that there are a lot of factors that can influence the signal from an object, so we can't be absolutely certain about many targets. As an example, maybe a large nail has deteriorated because of rusting and as such, maybe it creates a high tone a a different setting as most other nails. This can and will happen not only to nails but to other objects. The point being, there will be reasons some target doesn't seem to fit what you have learned initially.

Well, that is about all for now.

Reg

Reg,

I think a bit more clairification is needed here, not only for others but myself as well.

When doing these adjustments to the Ground Balance, the Conductivity switch must be set to ALL. Correct?

In bad ground (highly mineralized) it is impossible to hunt with the machine that far out of GB. The tone will WAW up and down as you swing because it's out of balance. Therefore, the ID method of changing the GB works to identify a potential target within a small area, pinpointing. When you want to continue hunting, you must return the machine to the proper GB. Besides giving you the smooth quiet threshold you need to hear those weak, deep signals, it gives you the best depth potential. At least that has been my experience here in the gold fields. Correct?

Digger Bob

Hi Digger,

Normal procedure is to properly ground balance when hunting and yes, any change in the GB should be done in the All mode if you want to see how much of a change or signal you get when trying to hunt. When nugget hunting this is generally the best technique to use in your setup.

However, as for silver or copper coin hunting in a park or maybe in a ghost town, in many places, you can set the detector GB to some level other than the ideal setting such as a GB setting of 4 or so and use the high conductor mode just fine. I have yet to find any place where I can't do this. One reason it can be done is because the normal tone change is a variation of a high tone ground signal change but in the high conductor mode, this high tone is ignored. So, one doesn't hear much of a ground signal if any. Again, this is true providing one uses good sweep techniques where they try to keep the coil level over the ground.

So, the TDI's usually will work fine with the GB offset downward when operating in the high conductor mode. The TDI SL may be more temperamental depending upon whether it is one of the very early units or one with the later mod installed. In either case, a nice slow level sweep speed works best and provides the best results.

I have been ridiculed for my statements that a nice slow sweep speed is the best to use on the SL to minimize odd signals, but the truth is, the design of the detector is obviously different than the standard TDI and because of this difference the SL is much quieter. Now, on the down side, this difference has a negative effect and that is, any fast movement creates certain things to happen, none of which are in the best interest of the detection of targets.

Now, too fast of a sweep technique can cause odd signals or at the other extreme, blanking of a good signal or half of a good signal, meaning you may get a one way signal. If this occurs, simply try a little slower sweep speed to see if that is causing this to happen.

On the early SL, any rapid movement of the coil could cause an odd signal to be heard more frequently. A minor change was added that blanked this odd signal. On the down side, this blanking is there all the time, so too fast of a sweep may cause blanking part or all of a good signal, meaning one may get a one way response or worse yet, no signal if the coil is moved too quickly and one is using the single tone mode and passes over a target of the opposite tone first close to a good target.

One other quirk that can happen on the TDI or the SL is when the sweep speed to a little too fast, one can get a short intermittent signal that may not be repeatable when using the signal tone mode. The more common reason for this is the odd blanking circuitry allows some bleed through of the trash response. At the extreme, any dramatic rapid ground signal change can cause the same thing to happen.

The key to getting the best depth regardless is to try to minimize any variation in ground signals. Even when the GB is set correctly, minor signals can occur if sloppy techniques are used when sweeping the coil. When the GB is adjusted off a certain amount from perfect ground balance, then it is even more important to minimize any sloppy sweep techniques and keep the coil as level over the ground as possible. In really bad ground, raising the coil a little helps also.

I mentioned these issues because some people are not sure where some of the intermittent odd signals come from and have questioned whether something is wrong or not with their detector. No, there are not problems with the detector, but in most cases these odd signal are telling you there probably is another target nearby or the ground signal changed significantly. They are also a good indication one may be sweeping too fast also.

So, in a long winded way, I am saying that one can operate with the GB adjusted off from the ideal setting and the detector work fine if the detector is operated under the right conditions and settings.

Reg

Thanks Reg and Digger Bob for your insights and sharing your knowledge.

I have read every post of the TDI Classroom and UNDERSTANDING THE PI METAL DETECTOR By Reg Sniff.
Y'all have provided so much information it is hard for my brain to absorb it all. LOL I have been cutting and pasting to build a reference file.

I may have over simplified the ground balance adjustment because my focus is on coin and relic hunting in relatively mild soil.
I doubt I will ever run across raw gold or silver.
I don't care to dig small targets (BB size).
I am strictly land hunting.

Part of the reason for my post was to ensure I am comprehending how a TDI works as opposed to a VLF which I have used for about 7 years.

I should have a TDI SL in my hands next week.
Then the test begins, one I am looking foward to, hope I pass.

HH
Fred

"So, the TDI's usually will work fine with the GB offset downward when operating in the high conductor mode."

So, since most nugget hunting is done in the Low mode, and sometimes All, the high conductivity trick to ID iron doesn't work that well for nugget hunting. Again, unless one wants to change settings every time to try to ID a target. Correct?

And I agree totally that slow is the way to go. I've demonstrated that in my video and in field tests under actual conditions that small targets seem to jump out better with a slow sweep. Of course, this isn't always a practical way to hunt. You need to cover ground. But for patch hunting, bedrock, or any small area, it will get you more gold.

Digger

You're welcome Fred. Reg is the real technical expert. I just use it and learn from trial and error. Also, I am not a coin hunter with it so that aspect is beyond me. I just use it for nuggets and have a regular coin machine for when I want to do that.

Digger Bob

Hi Digger,

I hunt the parks here in Colorado in the high conductor mode with the GB offset to about 4 or so and it works fine for me. I have used the same setting in AZ and in a couple of ghost towns also with success. In all places the stability was really quite good.

Now, one thing I have also done is sort of swap things. By this I mean, when hunting small gold, I have tweaked the GB up a little past the normal GB setting to help reduce some more of the iron objects while hunting in the low conductor setting. This has also worked for me in some places.

Going back to coin hunting in a park I might even advance the delay to 15 usec or so to minimize signals from tin foil type targets blanking deeper silver or copper objects. At that later delay and set in the high conductor mode, I get fewer false blips also. Since my SL is modified slightly to detect even smaller gold, I can't go quite as far on the delay as I could before. The trick when advancing the delay is to just go far enough that you can still adjust the GB to ignore nails. Remember, as you advance the delay, the GB setting that eliminates nails will drop to a lower GB setting than the one that works at the 10 usec setting.

Now, because it is difficult to pinpoint with a large coil, I sacrifice some depth and use either a Jimmy or the 7 1/2" DF coil when park hunting. I lose maybe an inch or so depth, but I still get signals deeper than I care to dig as it is.

Since using the TDI and SL for coin hunting, I have gone back and tried several VLF's again and personally I find I dig less trash and more old silver with the TDI or SL. So, I have again, mothballed my VLF's.

The only place I didn't use my SL much was on a trip to New Mexico in search of gold nuggets where the gold at our location was fly speck size. The SL struggled to give even a whimper on the largest piece found with a drywasher, so I had to use a VLF there.

On a different note, I tried a li Ion setup on my SL that worked fine. There is one made that works on the other White's units but I didn't notice it until I built my own. I like the setup but I don't expect the batteries to last more than a couple of hours of constant use and then I will have to change them. This setup uses the same size battery, the 18650, as used in the battery pack for the TDI, but only uses three of them. This setup gives a longer solid 11V+ than other battery setups.

Now, I thought I would try something else so I tried paralleling two sets of 4 Li Ion batteries in series. I used the 14500 size which are the same size as the AA. By modifying the battery case, I was able to do this only to find that I can't find enough good 14500's for it to work right. It seems at least one of them dies quickly and as such, the pack fails. I even tried reducing this to two series packs of 3 of the 14500's and got the same results. Maybe if I could find some good batteries to begin with, this might work but that hasn't happened so far and all or most I have ordered came from China, at least on Ebay that is true.

I thought the 14500's would make building a pack much simpler, but that hasn't been the case.

So, for those of you out there who are willing to try the Li Ion pack already made that should fit fine, you can. Here is a link to them. Now, I haven't tried them specifically, but have tried a home made pack that is similar and mine works fine. If quality batteries are used, I would expect maybe 3 hours actual on time max before charging would be required.

http://rnb-innovations.com/

The TDI already uses Li Ion batteries, so a longer run time is available but at the expense of more weight. In either case, the TDI or the SL, when the batteries get low, but not low enough to trigger the low led indicator, the detector will become less stable and begin to lose depth. So, when in doubt, check or replace the batteries to minimize any extra noise or reduction in depth.

Reg

Hi Fred,

Here is something else to remember when using the TDI or SL. The GB control also adjusts the depth an object may be detected. In some cases, this is quite obvious while in others, it may not even be noticeable. The trick is to remember a couple of things as to which direction you want to adjust the GB for maximum depth.

Now, with that said, the key is to remember which tone you are hearing, high or low. If in doubt, use the single tone mode and it will tell you. Now, the tone difference between a high and a low tone may be so slight on deep targets it can be mistaken for the wrong tone. So, the use of the single tone feature is a safe way to know for sure. Always remember a low conductor will have a high tone and a high conductor will have a low tone and this means the tone will increase or decrease in pitch depending upon the type of target.

Now, some people don't understand why the tones are the way they are, but it has to do with the original design which didn't have any ground balance. On those detectors the tone was a high tone only. So, when ground balance was added, and minimal GB possible was used, the high tone was still the only tone. As the GB was increased there came a point where some objects switched tones, thus the low tone was born.

If it were possible to adjust the GB to an absolute maximum, all signals would be a low tone.

Since the GB control has a very limited range in comparison to the range from no GB to maximum GB, one can't adjust across the entire possible range, but only adjust across the range needed for ground balance with plenty of extra to spare.

So, we are limited in just how far the GB can be adjusted both maximum or minimum on the GB dial. In that range, certain objects will change tones, but all objects will not do that. Something like a silver dime or larger silver coin will always be a low tone. A nickel or a very small gold nugget, on the other hand will always be a high tone.

So, highly conductive objects that are large enough will be a low tone and low conductors that are low enough will always be a high tone. Again, this means, small gold or gold that is quite impure and/or porous will most likely be a high tone throughout the GB range.

Now, getting back to what I was originally discussing, the GB control will affect the depth of detection of a target based upon the tone and which way the control is adjusted. Here is the key to remember, a high tone will become an object that can be detected deeper by reducing the GB control but will lose some depth if the GB is increased. Keep in mind the amount of depth change may be very minimal to quite significant and depends how close the object is to the tone change setting.

Now, for high conductor objects, the opposite is true meaning an object that is a low tone will increase in depth as the GB is increased but will decrease as the GB is reduced. This is why a silver dime may increase in depth of detection when the GB control is adjusted from a GB setting of 4 to one of 8 or so. So, at normal GB setting, a silver dime will give a strong low tone response, but so will many trash items such as nails. Reduce the GB to the point where nails are not heard and dimes will still give a low tone but will lose depth of detection.

Given the above information one might wonder why if most gold is small, why I would decide to adjust the GB more towards maximum rather than the other way. Well, the answer is simple, the depth loss isn't that much on most small gold and only becomes a big problem as the gold becomes large enough and the purity is high enough that the gold can change tones within the GB range.

On very pure gold, this tone change range is somewhere between 1/4 oz and 3/8 oz. Anything less than 1/4 oz usually won't lose much depth. At the same time, some small iron junk may be a high tone at the normal GB setting, but may change tones very close to the normal setting, so increasing the GB a little just might help reduce some of the junk I find and since there is a lot more junk than gold targets out there, I prefer to minimize the junk I need to dig.

Now, to be safe, one should experiment with what I just said in this post so they better understand what can and will happen. Simply taking my word for something can leave a person in a position where they may miss a good target and not know why.

Also, keep in mind there are other telltale tricks and things to remember that will also help in determining more about a buried target and these tricks should be used also, but before than can be used, they have to be discovered. That is where practice and experience comes into play.

Reg

Reg,

I plan on setting the delay around 16, I don't want to dig BB sized targets, but will I loss much depth? 10 to 12 inches should be more than enough. Small targets that would be great to save are percussion caps, 3 cent pieces, and cuff buttons. These all should be low tones. The 1$ gold piece I will need to test, it might be a high tone. Lead bullets of various sizes will also have to be tested with various GBs for tone and depth.

I have been collecting posts about changing the delay and conductivity once over a target to help determine ferrous vs non. Also your tip to use the coil's edge to determine depth.

Real world experinece will be the only way to learn the full potential but the posts and forum sure does make the learning curve shorter and more fun.

HH
Fred

Fred,

I suspect the three objects you mentioned, the three cent piece, the percussion cap and at least some buttons will be low conductor type signals and therefore will be high tones at normal ground balance. The $1 gold coin will be a low conductor target also. Three ringers should be high conductors or low tone signals.

A silver coin will become a low conductor if small enough. This is true of other more typical highly conductive objects. This is why gold, whether it is a coin or a nugget can be either a low conductor or a high conductor depending upon its size, weight, purity and other factors such as shape and the structural characteristics. On coins, the results are more standard, with a $5 gold coin generally a low conductor but the $10 being a high conductor. Since the $10 gold coin is basically a half oz of gold one would think that most gold nuggets in the half oz range would be low tone signals also, but that isn't necessarily the case.

The point I am trying to make is one should test each and every target one might be looking for to get an idea of what to expect, but at the same time, don't be upset or confused if a target simply doesn't seem to fit. A large nail may respond as a low conductor but one similar that has rusted dramatically may respond differently.

One should also evaluate a signal width as well as lifted coil signal intensity if they want a better idea of what might be hidden. Again, when it comes to ferrous junk the amount of rusting can influence what one might think would be the norm.

Sometimes using a straight mono coil can help also, but again, this takes practice. Then there is the testing of a target by approaching the buried object from different directions and listening to the signal response.

Regardless, the best determination as to what is hidden is to simply dig it up and look at it.

So, the learning curve of the TDI, the SL or any other detector for that matter is much more thorough than many people realize. All this is further complicated by multiple objects very close to each other. In such cases, a good target could be masked by a piece of ferrous junk. As a general rule, the signal from a ferrous object is much stronger than one from a similar size, shape and weight of a non ferrous object.

The bottom line is there is no perfect detector.

Reg

Reg,

I am hoping that by tweaking the delay and GB that I will be able to bring some of the low conductors into the high range. Lopsided to low tone/high conductivity, break point for GB to be determined, but positive of actual GB, delay started at 16. This is where I plan to start with some know targets.

Fred