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TDI- Pulse Settings For Relic Hunting - No Iron Switch!!!

I been very pleased with the White TDI -Pro in bad and good ground. Most all whom Relic Hunters I talked to hunt in ALL Mode. The most hottest subject that most relic hunters talked and "Don't Agree' on with is settings the the Pulse delay. White's Manual say set at 10s and maybe bump up an little if you dug nails, iron. Other such as myself seem to set at 15s-17s to knock out iron an little and few other say set at 25s. So what do exerts say about settings on TDI. The TDI would be great better machine is folk's at Whites would modified to some type 'No Iron' switch to not dig any Iron. But The Whites dealers has been bugging Whites to do such Modification to knock all iron but will not, WHY. Chuck


New member
I suspect Whites could easily add a no iron switch. Unfortunately, getting it to actually work would be the real problem since, so far, no one has been able to do that on a PI type detector that is presently for sale from a major manufacturer. One PI manufacturer uses a DD coil as part of its disc feature. Others may do the same or use similar means. Unfortunately, the DD setup is not foolproof and normally is limited in accuracy to shorter depths.

Now, if you or anyone else has a proven design, I am sure Whites would listen. So far, any accurate no iron design is not available as far as I know.

Picking the delay is sort of picking a wife. No two opinions are quite the same. To make matters worse, the iron and how it responds can change from area to area if for no other reason than the differences in deterioration of the metal. What might be rejected a little better at 10 usec, my not be rejected as well at a later delay. The same holds true for other metal where it might be ignored a little better using a later delay than using the minimum delay. Because of this, there is no perfect or consistent delay that will yield the best results as far as I know.

So, the problem is trying to figure out when to use the short delay and when to use a later delay. Add this to the personal preferences for other reasons and one is surely going to get different answers.

Sorry I can't be more specific but the facts won't allow it.



New member
After giving the question of adding a no iron switch some more thought, I thought I should add more information.

Right now, the conductivity switch along with settings of the Delay and Ground Balance control allow a person to ignore most iron objects. Unfortunately, the settings at which iron is ignored is dependent upon the three switches and they interact. So, trying to implement an iron ignore switch is not as simple as it might sound. To compound matters, some controls are in software and others are mainly hardware set. So, there would be no simple quick and easy way to do what you want.

Just as important, if you were to want such a switch, everything would have to be locked for such a switch to be implemented and this would require the lock to be at the setting to maximize the elimination of iron. This setting would not result in the greatest depth of detection of certain objects.

To both maximize the depth of detection and reduction of detection of undesirable objects takes knowledge of both the desired target and the detector itself and how it fundamentally works. Since both can interact, only the operator can determine what they feel is the best compromise. I don't believe it is possible for any other approach to work with maximum effectiveness. However, I could be wrong.

My personal opinion is the TDI is built for those people willing to take time to learn just how the TDI works, how the adjustments affect the detection of objects, and how each control interacts with others.


Seeing your quote about 'learning how the machine works,' I have a question that I hope you can answer. How does the conductivity switch affect the TDI. What changes when I switch from 'all' to 'high conductivity?' I know something changes because to balance out nails in 'high con' I have to set coarse GEB to about 2-4. To balance out the same object in 'low con' i have to set coarse GEB at about 8-9? What is happening? I'd like to know so that I understand why I am changing the settings, rather than just knowing to change the settings. Any help would be appreciated. I asked this same question on another forum and was referred to you.



New member

In simple terms that make sense, one can think of the conductivity switch as doing the following; the conductivity switch basically does nothing but shut off one of the tones when selected off the ALL position. So, if the conductivity switch is switched to HI conductivity mode, the high tones are shut off and only the low tones are heard. If LOW conductivity is selected then the low tones are shut off and only the high tones are allowed through.

Whether an object changes tones and just where it changes is determined in simple terms by how the object relates to the ground signal. The ground balance control is designed such that a secondary signal is amplified and subtracted from the main signal. When this secondary signal from the ground equals the main signal, the ground response is essentially eliminated and no response or minimal response is heard.

Now, the ground is nothing more than another target. The ground balance control is nothing more than the adjustment of the secondary signal that provides the necessary range of amplification to allow for this cancellation to occur. The range of this ground balance adjustment is such that certain other objects can be cancelled just like the ground signal. There are many objects than fall into this category and can be cancelled but there are also other objects that can't be cancelled.

A typical silver coin greater than a dime is one object that won't allow cancellation with the GB control. A small gold nugget is another object that will not be cancelled completely by adjusting the GB control through the full range.

What happens is, when this secondary signal is amplified it may reach a point on something such as the ground such that such that the secondary signal is to equal the main signal, and this allows for the cancellation. If that same secondary signal is amplified more, the secondary signal will be greater than the main signal and then will be the dominant response. If this happens, the signal becomes a low tone.

So, at a normal ground balance setting of 9 on the GB control, something such as a nail will normally respond as a low tone. Change the GB control and at some point less than 9, that nail signal will be minimized. Because of the strange response of nails a true balancing of nails is really not practical, but the signal can be minimized or at least reduced dramatically. At a setting of less than this balance point, the signal from that same nail now becomes a high tone.

Keep in mind that as the GB is altered, the signal from the ground is also altered. So, at a GB of 4, the ground will respond as a positive response. A GB setting greater than 9 will cause a ground response that is negative. This negative response may be more difficult to notice but it is there.

So, in effect, the ground signal can be a positive response, little or no response, or a negative response. Just which response the ground indicates will be determined by the GB control setting. This same condition holds true for other objects such as nails or many other objects for that matter. Since the GB settings were designed only to handle the ground, there is no calibration of other objects. So, it is up to the operator to determine how other objects respond by simply testing and documenting.

What complicates the matter is there are no absolutes, so any documentation will show that most objects that are not mirror images of each other may not respond the same. Exceptions are limited and fortunately, most US coins do display a level of consistency. So, something like a dime response will change very little. There will be some minor change when going from silver to clad but that usually isn't nearly as much of a change as the penny change that occurs when testing zinc, versus copper, versus copper Indian Head.

If you are a gold hunter, this target transition from low conductor to high conductor is far more complicated because of other factors. The surface characteristics, thickness, purity, and overall shape can cause two equal weight objects to react totally differently. In other words, a half oz nugget found in one are could respond as a low conductor while a nugget found somewhere else may signal as a high conductor at a normal GB setting of 9.

There will be a range of nuggets that will always respond as a low conductor, but a similar transition to a high conductor signal may never occur or require a very huge nugget to do so.

This same characteristic variation can occur on other objects such as buttons, etc. In the case of bullets, size becomes a factor as to where they change from a low conductor to a high conductor. Shape may also be a factor. In other words, a dropped mini ball may not respond identical to a bullet that has flattened from hitting something.

So, this change from a low conductor signal to a high conductor signal is something a person should try to determine when trying to focus on finding a particular object. Something as basic as the orientation of the object in the ground can have an influence, so one shouldn't be alarmed of a target doesn't react like one might hope or expect. This is further complicated by the fact that other objects within the field of the coil can also alter a target's response.

In other words, in simple terms, there is no way to determine just how any target may respond. This especially holds true of similar type objects made by different companies or out of different materials.

I hope this helps clear up what is happening. Any further detailed explanation would probably take a book which I really don't feel like writing at this time.



New member
Chuck, This is Tex, Iron will never leave you with the pulse delay. You will only make the detector less sensitive to small non ferrous targets. The GB setting plays more off a roll.When we first started testing the prototypes in the worst of ground in central Va. we dug less small iron . I also noticed if you used a mono coil instead of the stock 12 inch coil you heard more iron. The dual field coil is the only way to go. The pulse delay will help you with ground balance when using a large coil. To make iron go away?? Not possible with a PI as of yet. Even the Minelabs dig iron .

Daniel Tn

Active member
This can be done to some degree with PI machines. On the GPX series machines, you have an iron discrimination feature that isn't exactly bomb proof but its good enough to null out nails. As a relic hunter that's all I really want knocked out anyway. Bigger iron is also pretty easy to tell; such as horseshoes and such. Can it be fooled? Yes. But it is a long ways past what you are limited to on the TDI.

I put on the Spot a post about talking to some of the high ups at Minelab about using the GPX iron disc platform and coming out with a more affordable PI machine that could disc iron. I feel this is a niche missing in what is currently available and I believe it would be a good seller.

Whomever can come out and develop such a thing, would attract the attention of a lot of people. The TDI is certainly no slouch on depth...its downfall is the inability to discriminate iron, as mentioned here. You CAN fool around with the GB settings and make it more/less sensitive to certain items but this in itself is far from discrimination AND IS LIMITED to what version of the TDI you have. Since the introduction of the original TDI (the tan one) there has been at least 3-4 upgrades to it, NOT counting the Pro version of it. Each of these machines will behave differently...they even have different audio when compared to one another.

Case in point...the videos I shot with my TDI showing the difference between a nail and bullet. That particular machine was one of the earlier models. It wasn't the tan one but one of them that had the original small black knobs on it. It has a more lower toned sound to it and not a somewhat motorboating threshold. With it, it was VERY easy to hear the difference in a nail and minie ball. What I didn't realize was, that the newer TDIs weren't like that. I didn't find this out until we bought my wife one of the newer ones and it came sounding TOTALLY different than mine did. It has a more higher pitch tone and the threshold runs absolutely smooth as can be on it. On that particular machine...and the others I've seen just like it, it is EXTREMELY difficult to hear the difference in a nail and bullet. I actually took my machine and her machine and ran them over a nail standing in the same exact spot. My machine would give a very distinct short double blip on the nail. Hers would only do it if you held your mouth just right, other wise it sounded like one single beep just like a bullet. Not only that, but I noticed Tex suggested once at one of the DIVs, to turn the GB control up to around 10 or so and to hold the coil a little above the ground. What this done, was pretty much eliminated nails and you were still able to hear bullets and such. On his particular machine it worked pretty good; his is one of the earlier ones that was tan. On my unit and the ones thereafter, it wont work as good as on his. They are actually almost unhuntable due to ground noise when you do that.

There was another "trick" that involved turning the GB to around 4 with pulse delay at 10. Then flipping the machine into HIGH conductive only. What this done, was made most nails start to give a high tone as if the machine was over a button or something...therefore if you put it into HIGH conductive, you simply didn't hear the nails. BUT the extreme trade off was the horrible loss of depth. On a bullet you would only pick it up about 2-3 inches. Other wise, if it were deeper than that, it too would give a high tone that you never heard if running in HIGH conductive only. I never particularly cared for that method because of that.

So addressing the original question at hand. I have no idea why the manufacturers aren't racing to get a PI machine out that can discriminate iron. Whites has a great opp to do it and as you've said, they seem content with the current TDI platform unless they are just being super quiet about it. Minelab is sure not interested...they more the less said that their current GPX machines hadn't caught on well in the US and that they were selling pretty good in other countries. And if they even looked into such a machine, it would be years from now. Because as they put it, they didn't think there was enough interest here in the US for them to develop such a machine.


New member

First, there should be no reason why the later TDI's respond differently than earlier ones. Yes, the audio may be a little different tone. Yes, the actual means at which the delay or some of the other signals are generated, but the actual results are based upon the same design. So, there are other reasons involved as to why you weren't able to duplicate the results of your earlier tests with a later model.

As a example, the double blip from a nail is the result of the actual nail signal as it is seen by the receive circuitry. Pass over that nail from the wrong direction and you will get a single blip. Pass over that same nail from the right direction from either the old design or the new design TDI and you will get a double blip.

I have both one of the early designs and one of the new designs so I will double check this but I don't expect any differences. Why? As I said, the fundamental electronic design of both is the same.

Now, as for your concern about a discriminating PI, well, are you telling me that the ML will discriminate iron when using a mono coil or does it require a DD coil? I strongly suspect it requires a DD coil, which works on the principle the signals differ between a ferrous and a non ferrous object within a certain distance from the coil. This is a well known fact. That happens on the TDI also, but it isn't maximized since the DD was primarily designed to minimize the ground signal, something the TDI does superior to the ML in most cases while using a mono coil. Stick a DD coil on a TDI and much of the near surface ferrous trash becomes easy to recognize.

Your assumption is that manufacturers are not interested in building a discriminating PI. Well, you couldn't be more wrong. The truth is, it is not as simple as you might think and most manufactures haven't figured out a means of doing it consistently.

BTW, I mentioned this before but Eric Foster built a discriminating PI back in the 80's that worked fine on a clean beach free of ground minerals. Unfortunately, take that same detector inland and it sucked about the same way an old TR type detector did. Ground signals simply made the disc feature not useable.

Dave Emery has been working on a discriminating PI for years now. Most people who have followed that history know it as the Pulse Devil. Later versions are now called the Nemesis. Does this detector exist? Yes and several people have seen a working model. Will his design really work? Yep, it will. When will it be available? Only Dave can answer that. We have been waiting for years now for reasons I won't go into. Regardless, it will be when Dave is ready and able.

Now, getting back to your statement that depth is lost when using the TDI disc function. Yep that is correct. It has to do with the concept of how the disc feature works. Keep in mind the disc feature is really the ground balance circuitry and that was designed with the intent to minimize ground signals, and not to discriminate. Also, keep in mind the TDI was originally designed for gold hunting. Set the GB at the normal 9 on the control and the depth on something such as a bullet is quite decent. So, it just so happens the design allows for what is available but wasn't ever designed to be a discriminating PI. In fact the concept of using the TDI with a form of discrimination didn't exist except in what some people had noticed. The single tone feature was added just before the introduction of the TDI and was never part of the original design.

Can the TDI be modified to go deeper? Yep. Can the depth come closer to that of the much more expensive PI? Yep, but in doing so, the ground balance suffers as does any disc feature that is presently available. Is it possible to maintain some of the disc feature and get more depth through mods? I think it can and I may try working on that concept using a few ideas I have. Unfortunately, too many personal problems have gotten in the way with some still pending that have to be resolved first.


Daniel Tn

Active member
"Your assumption is that manufacturers are not interested in building a discriminating PI. Well, you couldn't be more wrong."

That is a big negative Reg. That isn't my assumption. Those are the direct words that were used in my emails back and forth to Minelab.

First, there should be no reason why the later TDI's respond differently than earlier ones.

That would be correct. There SHOULDN'T be a reason why they respond differently but THEY DO. I have personally owned 3 different TDIs over the past couple of years. All three of them behaved differently. Not only that, but shoot Carl an email about them and you'll see there have been several minor upgrades since the first release of them. If they are upgrading them to make them better as they go along, via software updates, etc, then they are going to behave different to one extent or the other. I wont base my findings on this from just 3 machines though. When I did the TDI videos it put me on the map so to speak as a "goto" guy for help on them. I attend the DIV relic hunts in Virginia and in the last few years, pulse machines have taken over up there. Out of 300 participants, I would estimate 225 of them have pulse machines now and most of them have TDIs. Since those guys and gals know me from the videos, I would get stopped quite frequently by folks that had questions about the TDI. So over the past 6 hunts or so, I have handled a bunch of other TDIs in showing their owners how to set them up right and trying to show the differences from target to target. From one machine to the other, they do vary...and in some cases, pretty big differences. Of the three I've personally owned, if you put them all on Pulse Delay 10, they all three would GB in the same spot at different places on the dial. I had one that would GB at 7 at 10 pulse delay....had one that would GB at 8 1/2 at 10 pulse delay, and the last one would GB at 9 right on the dot. Some simply ran smoother than the others too; this last one we had would run smooth threshold no matter what you done to it. The other two were wavery.

"Stick a DD coil on a TDI and much of the near surface ferrous trash becomes easy to recognize."

That is also a negative. I own the GPX 5000 and have had the opportunity to put several DD coils on the TDI now. Believe me I have played around. I've put the 11" DD Commander coil on the TDI, have put the 5x10 CoilTek Joey DD on the TDI, have tried the 8x5x11 CoilTek Platypus DD on the TDI, and also another of the Commander coils that was the 15x12 DD. So there you have 4 different DD coils of various sizes and manufacturers that I've tried on the TDI. In my test garden and in the field, there was no difference in audio on the TDI per targets. I actually was hoping there would be but at least on these 4 coils there was not. The only difference I saw was the 15x12 DD made it somewhat less sensitive to the square nail but the weight was the horrible trade off.

On a side note, I have also tried a couple of Mono coils on the TDI and was truly impressed with the overall depth gain of the RazorBack coils. I put a 8.5x11 RazorBack mono on there and it made the TDI come to life on depth to smaller things like buttons and such. It actually bests the 12" stock coil and is smaller and lighter weight. A friend of mine recently bought a 5" mono coil by RazorBack and it too is something to behold. BUT it was just a gain in depth/ground coverage vs the DD coils of the same size. If you put a straight mono coil on the GPX machines, they too will perform better in sensitivity and depth.

As you noted though, the GPX will only work in discriminate mode with DD coils. But that is no problem to me. The stock 11" DD coil on the GPX will blow a TDI with its 12" stock coil away in depth and signal strength. I've never dug a bullet at 18+ inches with the TDI but I sure have done so with the GPX. I will take a depth loss over the mono coils though, for the ability to discriminate iron out. After you dig 100+ bullets beyond 12 inches in a weekend, it makes the body tired :)

I have ran into a big slow down at work and have had to try and sell my GPX but as soon as things pick back up I will own another one. Unless something better comes along between now and then, they are the pinnacle of PI machines right now. Everybody that has one don't want anything less, and everybody that has anything else and has seen what the GPXs can do, they want one.


New member

I am sorry you don't feel that I know what changes have been made on the TDI's, but it is a fact. I am aware of all including the minor ones and none of them will cause any significant differences. As an example, the TDI Pro does have a second GB control and does have a volume control, and does have a minor filter change which does make it a little more sensitive to small gold. Now, what you don't know is I installed most of those changes on my PI's way well before they were implemented on the later TDI's, so I know what they will and will not do.

Also, I tried the nail test on my surface mount TDI which is one of the later units and I got the double blip just like I expected. I also tried the DD coil and I can tell the difference in targets between ferrous and non ferrous but, again, the depth this is obvious is limited. I also know why you may not notice it but I will leave that to you. The fact is, there is a signal inversion on ferrous objects and it is there for a certain depth. It is also more obvious when using a round coil than an elliptical.

Sorry, you may be right about what ML would do or wants to do, but I really doubt they told you what they want to do. They probably told you they are not interested and did so because they can't build what you want. So, I stand by my position that if they really could build a discriminating PI they would. If they really don't want to be able to build a discriminating PI, then they are truly a strange company.

As for your $6000 detector "blowing" the TDI away depth wise, I certainly hope so. For that kind of money difference, it probably should dig your bullets also as far as I am concerned. Personally, I don't think anyone would or should expect a detector costing about 1/4 to 1/3 as much to compete directly, depth wise. Now, with that said, I personally don't believe your depth differences, but that is my opinion and that is based upon years of comparisons to different models of ML PI detectors up to and including the previous model. I have not tried to ran tests against the latest and greatest version.

What is obvious is you like your GPX and that is great. Enjoy.



New member
Regarding the ability for a (any) metal detector to eliminate iron, I personally cannot imagine that as being possible. Just today I dug up a piece of rusted iron in my back yard that signaled my TDI with the conductivity switch set to Low Conductor AND also set to High Conductor. I will try to attach a picture of it. It was approx. 1.5" x 3", and about 1/4" thick. I am sure most people have found steel and iron of different states of corrosion, registering all sorts of conductivity. So how any machine could eliminate all of these without affecting other metals of similar conductivity (like gold) would require magic.


Active member
bigchuckinva said:
The TDI would be great better machine is folk's at Whites would modified to some type 'No Iron' switch to not dig any Iron. But The Whites dealers has been bugging Whites to do such Modification to knock all iron but will not, WHY.

The WHY is simple; the TDI platform isn't easily modified for this purpose. Because the TDI GB can be adjusted to knock out some iron, people jump to the conclusion that it would be easy to somehow modify this to give both GB and iron disc. Conceptually it is easy, but when we built it, it just didn't work worth a squat.

But there are other approaches.

- Carl


Well-known member
He never went into any detail, but did say that the cost would be far beyond the budget of most any hobby detector hunters.
If there is anyone that understands all types of detectors, its George. I believe he filed a patent in 1978 for a, "discriminating time domain metal detector, also."
But you can make book, regardless of brand name, George is a "Red Shift" ahead of the pack.


Well-known member
until you hit minerals, [then the reading of the meter as to ferrous/non ferrous or not] was unreliable. You must be talking about my PPD1 non motion detector
that did not read foil, unless you really cranked up the power to just below the point to where it would pick up the ground. It only read ferr/non ferr by meter
with the triplanar concentric, and not the 11" mono. The detector had no delay or frequency control, used 8 D cell batteries {a 9 volt for the speaker}
and was a cannon on any target, regardless of composition. I remember digging 1.5" iron canister balls at close to 2 feet, and 2 piece brass buttons at 16 inches.
Thirty-two pounder spherical projectiles were close to 5 feet in the worst ground I've ever seen-VLF's of any design were totally useless, and this was using the 8" loop at,
Sabine Pass, Texas. About 8 months later Eric sent me the GS-1 prototype that ground canceled bad mineral, such as found in Central Tennessee, and it worked as
designed. It worked in extremely negative ground that produced relics like no one had ever used a detector there before. It caused quite a stir.
I wish I could have kept it, but I wrote up my synopsis, and mailed the detector back to his Stateside representative.
Would there be any advantage in a no motion design? I keep hearing there is no phase angle with a P.I., but is that an absolute? Are there other ways to go at
iron besides the current method {s}, expenses asides?