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White's TDI


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OK, so I'm just starting out with the GB2 and think this will be good for me for a while but was curious about the TDI. Is this a true PI like he Minelabs? I'm guessing it can't compare to a Minelab because a GPX is 5K and the TDI is $1500. I'm just checking it out maybe for the future.

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OK, so I'm just starting out with the GB2 and think this will be good for me for a while but was curious about the TDI. Is this a true PI like he Minelabs? I'm guessing it can't compare to a Minelab because a GPX is 5K and the TDI is $1500. I'm just checking it out maybe for the future.

It is indeed a good entry level PI from all the reports and has some interesting features and I am sure some users will chime in here, I have not tested the final version as yet myself.

If you are asking if it a step up from a VLF as well the answer it a definite yes if you will be hunting in highly mineralized soils.

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Hi wjbell,

Yes, the TDI is a true PI. No, it will not compete depth wise with the more expensive ML's, but it is no slouch either. In some places and under certain circumstances it will really excel when comparing PI's, but at other times, the TDI will look like it fails terribly. This can occur on a very specific size nugget and an associated ground balance setting. The trick is to know why and what to do to minimize any problems.

Now, as a PI, the TDI ignores many of the hotrocks or most black sand that plague the VLF's. Yes, there will be a few rocks that will generate a signal, but overall, many if not most will be ignored.

Keep in mind the TDI is noisier than the more expensive ML's when set at max sensitivity, and the max sensitivity is no where near the sensitivity of the more expensive PI's. As a general rule, PI's are more susceptible to external noise signals. On the plus side, the TDI doesn't experience nearly as much of a problem with certain EM noises as many other PI's. As an example, hunting under power lines is something that can be done with the TDI with no special adjustments. There is a manual adjustment called the frequency control on the TDI that allows the operator to minimize EM noise signals.

Now, a person can simply adjust the TDI to some recommended settings and begin hunting away. So, it can be a turn on and go type detector. However, to fully appreciate the capabilities, it pays to learn more about the detector since it can make a big difference in depth of detection of certain size or type gold. So, it is a turn on and go detector, but works best when specifically adjusted for the conditions. As a perfect example, lets say you head for an area where most gold is relatively small, but there are tons of nails. If the TDI is set up as typically recommended for a beginner, determining nails can be a problem. Nails, as well as about all other forms of metals including any gold nuggets will create a response. As such, it is up to the operator to either dig all signals or try to guess as to which are good and which are not. So, you hear signals from nails as well as from gold.

Now, with a flip of a switch, most nail signals are gone (yes, no signal at all, or at the worst level maybe only an intermittent signal) but small gold signals are still nice smooth signals at the original level before the switch was changed. Actually, the gold signals may be a little easier to hear since switching to low conductor mode will reduce the noise level also, making it easier to hear the very weak signals.

BTW, there is minimal discussion of the single tone mode in the manual. The reason is simple, it was a brand new feature added at the last minute to the TDI and not much was known about it at the time the manual was written. Even today, many experienced users fail to use the feature for one reason or another. Probably, the big reason is lack of knowledge of just what to expect or what should be done to assure or minimize the the possibility of ignoring desirable signals.

I personally use my TDI for other types of hunting including coin hunting for silver or older copper coins. In this case, I select high conductor mode, adjust the ground balance control to ignore nails and hunt away. No, I do not hear signals from things like nails, bottle caps, tin foil, pull tabs, etc but still get decent signals from the desired objects. So, I can hunt a park and basically ignore most junk.

Getting back to gold hunting, it pays to know more about the gold coming from the area where one is hunting. As a good example, I recently found a nice nugget (over 1/2 oz) that sounded off on the TDI as a low conductor. In many places a similar size nugget would sound as a high conductor type object. However, in the location I was hunting, the gold was rough and was alloyed such that even many of the larger nuggets responded more like a smaller nugget (sound wise) as far as the signal is concerned.

In this type of hunting conditions, the simple adjustment to make is to set the detector to detect low conductor objects only, adjust the ground balance, and hunt away. Setting the detector to this type of setting will allow the operator to ignore most nails but still get a decent signal from the local gold. When I say ignore nails, I mean you will not get a signal or not get a typical target signal from most nails. Instead, they are simply ignored or may respond intermittently as the coil has passed the object. This type of intermittent signal is easy to distinguish if it exists at all. Nugget signals, or signals from other non ferrous low conductive objects will usually be a nice smooth repeatable response. Now, one should realize that at this setting, you will also ignore any lost silver coins that may be in the area. Also, if there happens to be other gold that responds as a high conductor, it will be ignored also. Usually, the gold from a particular area is reasonably consistent so knowing more about it can make it easier to make certain adjustments.

So, I have mentioned low conductor objects and high conductor objects and the fact one can adjust the TDI to detect both or one or the other. So, what determines whether a target responds as a low conductor or a high conductor object? Well, that is determined by the ground balance control adjustment and the signal coming from the object being detected. Low conductor objects have a signal that stops quickly when analyzed, while a high conductor object has a signal that lingers a long time. When the detector is adjusted for proper ground balance, the objective is to balance out the ground signal so no response is heard. Now, metal objects can have a signal that is either shorter or longer than the ground signal. If the signal is shorter, then the signal is considered a low conductor object. Objects that have a signal that lingers longer, are high conductor objects. The low conductor or high conductor also refers to the ability to conduct electricity. I this case, good conductors such as silver and copper are usually high conductors, while lead, zinc, etc are normally low conductor materials.

Gold, on the other hand can be either a low conductor or a high conductor for the same size object. In other words, a 1/4 oz nugget could be either a low conductive signal or a high conductive signal, depending upon the characteristics of the gold itself. The characteristics that can influence this feature include the purity, the surface characteristics or even the actual specific mass structure. A solid lump may respond totally different than a specimen that has gold laced through a rock. Pure gold will clearly react differently than gold that has more copper or silver alloyed with it. What may seem odd is the more alloy of other metals has a tendency to reduce the conductivity even though the alloy by itself is considered a high conductor.

So, as I mentioned earlier, knowing more about the gold that comes from an area is an asset when hunting for the metal. One should also keep in mind this knowledge of the gold can make a difference with any detector and not just the TDI. What is better known is what happens on the TDI and how to maximize the adjustments.

BTW, this knowledge of strange behavior of gold and why certain signals change was not well known until fairly recently. Earlier, many people got poor depth responses from certain nuggets and blamed the ground conditions, when in reality, much of the problem was caused by this difference in conductivity and how the ground balanced worked. Yes, this strange behavior does effect other PI's. In fact, my first experience that strange things occurred happened many years ago when testing one of the earlier ML SD detectors. At that time, I noticed I had one nugget that seemed to be almost impossible to get a good signal from it. At the time, I wasn't sure why. Later I figured out that if that particular nugget had a similar response as the ground, then when the ground signal was ignored, so was the nugget. It almost feels like certain nuggets fall into a "hole" and can't be detected as well as others. This strange behavior does occur on the early SD's as well as the present TDI. So, it is something to keep in mind.

The later GP's take different ground samples and as such, reduce this strange "hole" feature that occurred on a particular size nugget. Now, certain other info seems to indicate that different "holes" still occur on later ML's depending upon the particular settings.

So, there is no perfect PI, but the latest ML's clearly do come the closest. The TDI isn't perfect, but knowing more about the limitations allows one to adjust the detector to minimize any depth losses. This may mean one may have to search an area more than once for maximum coverage. At least, this is what I have found to be true. Again, as a good example, the gold found on Rich Hill happens to be quite pure and as such, seems to change from a low conductor to a high conductor at about the 1/4 oz range. So, small gold in the few gram size or less respond like a low conductor while gold in the 1/4 oz range or larger has a tendency to be a high conductor signal.

Now, one would think that if such a condition exists then using the single tone modes would cause major problems. Yep, it can if one only searches an area once. However, lets say the area has tons of nails as well as gold. Now, one can hunt away and dig everything. To be honest, this gets old real fast after digging the umpteenth nail.

On the TDI, the trick I would use is to hunt once in the low conductor mode and then hunt again in the high conductor mode while ignoring nails regardless of the mode I was in. Yes, it can be done.

Sorry, to be so long winded in responding to your question but I thought I would toss in some info that doesn't show up as obvious in many discussions or in the manual. Nothing like adding more info to further confuse things.


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Great Post... very informative and helpfull, I have thought about another detector myself and right now can't see coming up with the cost of the latest and greatest detectors available :cry2: , like everyone else got too many bills to pay off. dang Economy...LOL but might be able to squeeze the cost of the TDI out of the ole better halfs hands :brows: and then work my way up to the big boy detectors at a later time..I have found loads of trash targets and lead but still no nuggets :inocent: . My son has already got 3 up on me right now. :grr01: (I know got to get the detector over Gold to find Gold) But I would love to have a good PI Detector to my inventory of prospecting gear to go with my Tessoro Tejon and Lobos Super Track, then my wife, son and I will all have detectors to swing.

Very Respectfully



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