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The White's PulseScan TDI was released in 2008 and is still in production as the TDI SL. Prior versions have been discontinued. I was one of the original users of the TDI and still dabble with them to this day. See my story White's TDI at Moore Creek, Alaska for pictures of lots of TDI gold nugget finds. I also have extensive notes on using the TDI for coin detecting at Steve's Guide to White's TDI Coin Settings. The TDI is a unique detector and is seeing use in many applications unforeseen when it first came out. The TDI has been available in several versions but all are basically the same detector as far as how they work. October 2019 Note: White's has a model called the TDI Hi-Q, which is a TDI SL with straight rod, new coil, and tan or camo paint job. See the details here. I am a big fan of competition as I always want more and better detectors from the manufacturers personally, and I think competition is the best way to get better detectors. After Garrett got into the ground balancing pulse induction (GBPI) game with the Infinium people including myself were really after White's to make an entry into the field. I went so far as to visit White's Electronics personally to lobby for such a detector with suggestions on how to get there. Alan Holcomb, the CEO at that time, flew me down at White's expense for discussions on how to proceed with such a project. In particular, I advised that rather than developing something from scratch, it might make more sense to license the existing Goldscan technology from Eric Foster, widely known as "the father of pulse technology" for his early work in the field. Eventually White's did decide to pursue the matter, and I was therefore aware early on that White's was working on a new detector, In 2007 I was sent a prototype unit to evaluate while I was on vacation in Hawaii. I was very impressed not only with the power of the detector but more importantly for me in Hawaii I was very impressed with how stable the detector was in salt water. It was also virtually immune to electromagnetic interference (EMI) issues that had dogged my use of other detectors in Hawaii. White's TDI SL with closeup of control panel (compare to original TDI controls below) My use of previous GBPI detectors, the Minelab models and the Garrett Infinium, made me familiar with how they respond to targets with various tones. Each target generates a dual tone that varies depending on whether the target is above or below the ground balance point that has been set. You will hear either a high tone followed immediately by a low tone (hi-lo), or a low tone followed immediately by a high tone (lo-hi). This dual tone system is effective for most uses but if you get into a target rich location it in effect doubles the number of audio signals coming from the detector. I also had an opportunity in Alaska to visit with Brent Weaver, the main engineer at Garrett responsible for the development of the Infinium. While testing a prototype Infinium I asked him about the dual tones (Garrett now refers to them as "echos") and whether they could be suppressed. He told me the dual tones were integral in how the Infinium worked and that it was not practical to produce a single tone result on the circuit they were working with. White's did end up working with Eric Foster on the development of the TDI. His method is one I like because instead of the dual tone responses generated by the Minelab and Garrett models (hi-lo or lo-hi) the TDI generates one of two tones, either a low tone, or a high tone. The tone depends on whether the target is above or below the current ground balance setting, and therefore there is only a tone difference when the ground balance system is engaged. The ground balance off, straight PI mode has monotone responses. Also, because the ground balance can be set manually on the TDI, this tone "breakpoint" can be shifted by the operator. This allows targets to be separated broadly into two distinct groups. On one hand there are high conductor type targets, like most coins and large steel items, that on the TDI produce a low tone response. The other group is comprised of low conductor type targets, and includes most gold items, US nickels, aluminum, and small ferrous trash. These all produce a high tone response on the TDI. There are far more high tone targets than low tone targets in most locations. I really liked the prototype TDI that I used in Hawaii, in particular the fact that it generated half the audio responses compared to a Garrett or a Minelab. Once again I wondered if one tone or the other could be suppressed. I sent an email to Eric Foster, and was surprised when he told me that not only could it be done, but it would be a very simple thing to implement with a basic toggle switch arrangement. This came about very late in the TDI development, and I lobbied hard for just such a feature to be added. A last second vote was taken by those involved, and probably the last major change on the TDI before it went into production was the Target Conductivity switch. There was no such switch on the tan prototype models. Prototype White's TDI Used by Steve Herschbach in Hawaii Now, I do not want to give the impression I was some kind of major player in the development of the TDI. I was just one of many voices pushing at White's for years to develop a ground balancing pulse induction (GBPI) detector. I am pretty sure though my last second inquiry and little push was what made the tipping point to getting the Target Conductivity switch included, and I think to this day it is one of the most useful and intriguing features on the TDI. It allows for a vast reduction in the number of audio responses in certain situations and in conjunction with the manual ground balance and pulse delay offers a degree of discrimination on the TDI not seen on any other pulse induction detector made today. This makes the TDI a pulse induction machine that can be used effectively for coin detecting, if the operator knows what they are doing and employs some smarts in site selection. I wrote an article entitled Steve's Guide to White's TDI Coin Settings on this very subject. I will not repeat the information here in the interest of keeping this page from getting too long so check out the link. Suffice it to say the TDI has the ability to play tricks and discern targets far beyond what most PI detectors can achieve. Another major feature on the TDI is the ability for the ground balance system to be shut off. The method used to ground balance the TDI in effect subtracts the ground reading from the total readings returned by the detector. This subtractive method does actually steal some depth, which is easily shown in air tests on targets with the ground balance turned on and the ground balance turned off. The closer the target is in relation to the ground balance setting, the more depth is lost. People find this very confusing, as the whole point of ground balancing a PI is to get better depth, right? Original White's TDI Control Panel The way it works is this. In low mineral ground a PI gets maximum depth without using any ground balancing. However, as mineralization increases, depth is affected. The more mineralization, the more depth is lost. Also, ground effects increase. In low mineral ground, the coil may be raised off the ground with little response. In highly mineralized ground, raising the coil even slightly off the ground produces a false signal. Nearly all PI detectors have an audio retune circuit that slowly retunes the audio response to keep it at the set threshold level. Otherwise circuit drift and minor ground variances would require constant retuning. In high mineral ground, the ground produces a response, but the detector compensates as long as the coil is kept at an exact height over or on the ground. If the coil is raised quickly, the audio overshoots when the ground signal is removed and a false signal occurs. This can be a real problem in even ground or in the water where it is difficult to maintain a steady distance above the ground or sea bottom. Hot rocks or wildly varying ground mineralization present an even greater issue. Again, the detector does well as long as the conditions are constant, but when a hot rock or mineralized ground condition like a clay seam enter the picture, a false signal is heard. In areas with lots of hot rocks PI detectors that cannot ground balance are almost useless due to the overwhelming number of false signals. So imagine a PI with no ground balance in low mineral soil. All is well, maximum depth is achieved. Pretend we have the ability via a magic dial to turn up the ground minerals and/or hot rocks in the ground. A point is reached where performance and efficiency is greatly impacted. It becomes impossible to discern good targets from ground signals and false hot rock signals. At such a point, engaging the ground balance circuit gains back the lost performance and efficiency. It does this by eliminating the ground signal and hot rock signals. White's search coils for TDI (from 2018 product catalog) This leads to situations occurring where people use a GBPI detector in low mineral ground and decide they are no better than a VLF. That actually often is true, in that a good VLF in all metal mode will do about as well as a Ground Balancing PI in low mineral ground, if both have similar coil sizes. A GBPI does not come into its own until the ground conditions or hot rocks are such that a VLF operator wants to toss the detector in a gully in frustration. This has been a very long lead explanation to the TDI secret weapon. In low mineral ground, turn the ground balance off! The detector will become extremely stable with a very smooth threshold and become more resistant to electrical interference. Gain may be boosted and a great deal of extra depth achieved in situations that allow for this type of operation, and they are actually very common. This would be the preferred beach mode on most beaches, the exception being beaches with a lot of black sands. The White's TDI in pure PI mode is one of the most powerful straight PI detectors available. The tone differences between targets disappear, and sometimes the ability to differentiate targets is more important than the depth gained by shutting the ground balance system off. But do not overlook this ability to run without ground balance in situations that warrant doing just that as it can really pay dividends to the knowledgeable operator. In 2018 White's responded to long standing demand from customers and released a version of the TDI that is waterproof to 25 feet - the TDI Beachhunter. This is basically a TDI SL in a Beachhunter ID control box. The model weighs more at 5.2 lbs for obvious reasons. The TDI Beachhunter has all the same controls as the TDI SL with the exception of the conductivity switch. This means the TDI Beachhunter signals on all targets, but the dual tone scheme remains to allow the operator to differentiate targets by the sounds. In order to help insure waterproof integrity the coil on the TDI Beachhunter (12" Dual Field coil) has been hardwired into the control box. Forum thread with more information on TDI Beachhunter. White's Electronics TDI Beachhunter - new for 2018 ~ Steve Herschbach Copyright © 2010 Herschbach Enterprises Official White's TDI SL Page White's TDI SL Data & Reviews White's TDI SL Instruction Manual White's TDI SL Special Edition Data & Reviews White's TDI BeachHunter Data & Reviews White's TDI Pro Instruction Manual White's Original TDI Instruction Manual White's TDI Field Manual Forum Threads Tagged "whites tdi" White's Metal Detector Forum Great Post on Batteries For the TDI SL White's TDI Coin Settings Some Commentary On TDI Tuning & Discrimination White's TDI Technical Specifications* Internet Price TDI SL $1189 (Special Edition $1049) (Beachhunter $1199) Technology Ground Balancing Pulse Induction (GBPI) Frequency 3250 - 3370 Pulses Per Second Autotune Mode(s) Slow Motion Ground Rejection Manual, one turn control Soil Adjust Ground Balance On or Off (two position switch) Discrimination Conductivity switch*, 10 - 25 Pulse Delay Volume Control No Threshold Control One turn control Tone Adjust No Audio Boost No Frequency Offset One turn control Pinpoint Mode No Audio Output Speaker, 1/4" headphone socket Hip Mount No (TDI Beachhunter - Yes) Standard Coil(s) 12" Round Dual Field Optional Search Coils Over 100 accessory coils available (TDI Beachhunter has hardwired coil) Battery Rechargeable NiMH & AA Operating Time Up to 6 hours Weight TDI SL 3.5 pounds ( TDI Beachhunter 5.2 lbs) Additional Technology The TDI was designed specifically to be able to use Minelab SD/GP compatible coils. However, performance can vary and the pulse delay may have to be advanced to compensate for coil differences that result in overload readings. TDI Beachhunter is waterproof to 25 feet. Notes *The TDI is unique in that it can suppress audio responses into two different classes. Targets have a high tone or low tone audio depending on how the target relates to the ground balance setting. In general high conductive targets give a low tone and low conductive targets a high tone. The TDI can be set to allow for one response or the other. See White's TDI Coin Settings for more details on this control. *Notes on Technical Specifications - Detailed notes about the specifications listed in this chart. White's TDI SL High-Q Tan metal detector

The two best-selling professional metal detectors in Alaska over the last twenty years are probably the White’s Electronics GMT and White’s Electronics MXT. This is because a set of local circumstances favored these two detectors. These two machines are based on the same circuitry, but have very different design goals and therefore features which determine which might be the best choice. Since the sole purpose of the GMT is prospecting, it operates at a high 48 kHz for extreme sensitivity to small metal items... hopefully gold nuggets. It is not a "gold-only" machine in that it picks up all metals. The "gold-only" detector has yet to be invented. It does however have a very efficient system for separating ferrous (iron or steel) items from non-ferrous items (gold, copper, silver, lead, aluminum, etc.) In theory the GMT could be used for other types of detecting, but it has a couple serious problems. First is the fact that it is so sensitive to small metal! Any attempt to use it for typical coin detecting would leave a detectorist quickly frustrated. Imagine a foil gum wrapper sucked into a lawn mower, shredded, and spread about. Parks and other areas popular with coin hunters are full of tiny aluminum trash. Every one of these items will sing out loudly on the GMT. Coin detectors are purposely designed not to pick up these tiny non-ferrous items as 99% of the time they are trash. The GMT also is very sensitive to wet salt sand, and so is useless for most beach detecting. It would not be impossible to use the GMT for other detecting tasks, but in general it really should not be considered for anything other than nugget detecting. The MXT was built using the GMT circuitry. An advanced LCD readout discrimination system similar to that on top-of-the-line coin detectors was added. The frequency was lowered to 14.7 kHz to increase the sensitivity to coin type targets and to moderate the problem of being too sensitive to tiny trash. But the frequency is still well above that of standard coin detectors which work around 6 kHz so the MXT retains much of the GMT ability to hit gold targets. The MXT has three distinct modes: Coin & Jewelry, Relic, and Prospecting. Each mode dramatically changes both the sounds and the LCD readouts generated by different targets. The Coin & Jewelry mode is very much like any standard coin detector, but with a better than normal sensitivity to gold coins and gold jewelry. The Relic mode is a rather unique dual tone mode that operates in both all-metal and discriminate modes at the same time. That alone is subject for another article! The Prospecting mode in effect turns the detector into a GMT, but one that runs at a lower frequency and that lacks a manual ground balance. And the MXT has a special Salt setting to allow it to work on those beaches. White's GMT versus White's MXT The GMT is admittedly superior when it comes to picking up small gold. It can hit specks weighing less than 1/10th of a grain (480 grains per Troy ounce) while the MXT will need nuggets weighing 2-3 grains to get a decent signal. But on the flip side, the MXT may very well be the superior unit for large nugget detecting. The lower frequency actually is smoother in mineralized ground, and in particular does not produce as many weak variations in the threshold in mixed cobbles as the GMT. The drawback of higher frequencies is that while small gold produces a sharper response, so do hot rocks. The manual ground balance on the GMT is very helpful for hitting those tiniest specks, but less useful for larger gold. If larger gold nuggets are the goal, then the MXT is every bit equal, if not better than the GMT in overall performance due to the smoother ground handling capability. It’s not that the MXT goes deeper, it just has less issues with hot rocks while still being able to hit those larger nuggets. In milder ground the GMT reigns supreme. For Alaska those wanting to go places like Crow Creek or Mills Creek and have a chance of getting gold, any gold at all, will be best served by the GMT, especially if paired with the little 4” x 6” Shooter coil. It will get the gold in these heavily hunted areas, and will hit gold the MXT will miss. But if versatility is important, or chasing large gold nuggets in tailing piles at Ganes Creek is the goal, the MXT is the way to go in my opinion. It is simply one of the best all-around detectors I have ever used. The White’s MXT Engineering Guide is full of interesting information on the development of the GMT and MXT and provides a rare look at what goes on behind the scenes at a metal detector company. ~ Steve Herschbach Copyright © 2010 Herschbach Enterprises