White's TDI Coin Settings and Target Responses

original post May 27, 2008 updated February 14, 2010

The White’s TDI is a pulse induction (PI) metal detector and as a rule these detectors are considered “dig-it-all” type detectors. The TDI, however, has a number of manual controls that can be adjusted to allow for a degree of discrimination not normally found in PI units. This method was passed on to through comment from Reg Sniff and George Kinsey so credit goes to them for turning me on to this.

This post is not a definitive end to the subject of coin detecting with the TDI. The method involves purposefully misadjusting certain controls to get results and I’m not saying these are the best settings per se. I would encourage more experimentation to see what you can coax from the Whites TDI as I have not seen a detector so prone to experimentation for some time and yet with relatively few controls.

I highly recommend the use of a PI pinpointer with the Whites TDI. You need some serious pinpointing power. The Uniprobe units are very good, but you may need to switch the TDI off when employing the Uniprobe pinpointer if the TDI interferes with the Uniprobe. Coiltek makes a 1” probe with switch box that can use the TDI itself as the pinpointer as another option.

With the unit powered off, set the TDI Gain at 12, Pulse Delay at 10uS, Ground Balance knob at 1.5, GEB switch On, Target Conductivity On, and then turn the unit Power On. Set for a faint Threshold. If you are getting any interference (uneven threshold, warbles, and funny noises) slowly run the Frequency knob through its range seeking the quietest setting. Then flip the Target Conductivity switch to High. The threshold should go extremely smooth. If you get spikes or noises breaking through the normally rock solid threshold you may need to reduce the Gain. But usually at this point the threshold will be so smooth and solid you will find you can reduce it so low as to be barely heard.

Now try waving various steel items and coins a few inches under the coil and note the responses. You will see that most steel and iron, aluminum, and bottle caps will not signal. Beyond that, there are three basic responses. First, hold a coin 6-8 inches from the coil. Note the soft, sweet tone, woo, woo. Listen to it over and over, as this is your deep coin signal.

Now run a coin or larger steel item within 1 inch of the coil. You will get an overload signal, a strong baaaaawo, baaaaawo. This is the shallow item overload signal. If you are trying a steel or iron item, increase the distance from the coil. Note that at a certain distance it abruptly cuts off. Now try a coin and slowly increase the distance from the coil. It will gradually turn into that sweet coin tone. The way you tell shallow coins from shallow junk is to slowly raise the coil. If the target just cuts off – junk. If it slowly mellows out – dig!

OK, let’s go detecting. Listen for that sweet, deep coin sound. Those are the oldies and you main goal. In some hunted out parks this may be about the only signal you get as there are no shallow targets to generate to overload tone. Just go dig coins. Walk around each target and insure it gives a good, clean response from all angles. Be sure and use proper digging practices to leave the ground undamaged. Save our hobby!

In other places you will get lots of overload signals. If all you care about is deep coins, ignore them. If you want, however, just raise the coil while sweeping, and if the signal cuts off, skip it. If it fades to the deep coin tone, use your pinpointer and there should be a coin within an inch or two of the surface you can just pop out.

The Target Conductivity switch can be set too All to investigate questionable targets and to size targets. A pipe buried horizontally will have a high tone its entire length but a low tone at each end. When you walk around these in the High setting you will only hear the low tone and think it is a coin, but they tend to fade in one direction as you walk around them. If the target seems iffy, switch to All and see if you are picking up the end of an elongated iron or steel item. This false positive can occur well off the end of the pipe and so if you dig and nothing is there you may be off the end of a pipe or rebar. This is where a top notch pinpointer comes in handy.

The Pulse Delay seems to be most critical, and if you set in much higher than 10uS the ability to ignore iron is lost. But when it is working right the iron rejection is amazing. Try walking up to a garbage can or other large steel item. You will get no signal until you get close enough to overload the unit.

Not only does the unit ignore iron, but nearly all aluminum and bottle caps. The only ferrous target I found was a very rusted bottle opener buried vertically in the ground. If flat it is rejected but the TDI does pick it up if held vertically. I never did dig a bottle cap. I did get two aluminum screw tops that gave the shallow overload and that then sounded like shallow coin when the coil was raised. I got one older aluminum screw cap that was not deep or shallow so I checked it out. I also got positives on two copper wires, two chunks of broken heavy aluminum, an aluminum grommet, and a copper screw cap.


Oh yeah, I found 39 coins. That is 39 coins to 10 trash targets using a PI detector in a turf setting. That is a four to one ratio, and when hunting the deepest targets no worse than a VLF. Better yet, the targets that fooled me were not exactly bad targets by deep detecting standards. Three weeks ago I would have said this was impossible. I really did feel most of the junk was iffy but I wanted to check as I am learning. Coins sound oh so sweet and when I’m 100% sure it is a coin it almost always is.

What else to say? The GB control is in effect the discrimination control. It is all about setting the Pulse Delay, the GB control, and the all new Target Conductivity switch to get the best balance of depth and iron rejection. The iron rejection tends to be best at low GB settings, and in high mineral settings best depth is at high GB control settings. If you have no clue what I’m trying to say, you are not ready for the Whites Pulsescan TDI. In high mineral conditions you are trading max depth for max iron rejection. You have to set the unit for the best balance for your conditions. But if you get it right, hold on. This detector is like no PI you've ever used.

I have been able to run the Gain very high. I’m sure not everyone can based on where they are. So experiment, experiment, experiment! What about coils? Things might change depending on the coil you use.

I do not want to give the impression I am pushing the TDI as a coin detector. If you want a detector strictly for coin detecting I suggest you get one to do just that. One real drawback to this method is it gives up a portion of the depth one would expect of the TDI if tuned properly for depth. By setting the detector to reject junk items you end up with depth no better than a good coin detector. The real point of this post is to highlight that the TDI is a unique detector prone to experimentation. It is a machine for more serious detectorists willing to think outside the box.

The main use for the TDI is still nugget, beach, and relic detecting, make no mistake about that. But if you have one, it can pay to experiment with it as there is really nothing else quite like it on the market. Thanks to White’s Electronics and Eric Foster!