White's TDI seems to have pretty good discrimination when using a DD coil

[AlexP]

I got my White's TDI a couple of weeks ago and had started to get desperate and was even thinking of selling it because of its lack of usable discrimination (I don't think that I will ever get used to kind of discrimination it is supposed to have, as explained on this and some other sites - by switching to high conductor and offsetting the GB). Plus, here in Bulgaria most coins a low conductor coins and if I switch to high conductor only, I'll lose the ability to detect them, not to say that when you offset the GB, the depth decreases also. But yesterday I went out to hunt for coins with a buddy who has a ML GPX-4500 and he was laughing on me how useless the TDI discrimination was and said that I should have bought a GPX instead. I was using the standard 12" concentric coil. At some point we decided to try the GPX 11" DD Commander coil on the TDI, and what a difference - with the target conductivity switch set to ALL the detector produced wavy (changing pitch) sound on every ferrous target we tried it with - various iron coins, small and medium sized nails and some others. And the signals from the non-ferrous objects were clear and stable and the pitch was not changing on them. We didn't bury the test targets. Just put them on the ground and tried sweeping the the coil at different heights over them, so I believe it should be the same as if they were buried. I am going to get a DD coil for my TDI now.

Have anyone of you tried using a DD coil on the TDI and got the same result?

 

[Reg]

Hi Alex,

Yes, I have noticed the ability to distinguish most ferrous objects from non ferrous using a DD coil. This distinction does have a depth limitation, but overall it works quite well.

Now, the nice thing about the TDI is the ease of building coils that will work on it. So, if none are available one can always make their own if they have the basic soldering skills. This is something that can be done easily on the TDI but not for the other detector you mentioned.

Don't give up on the ability to differentiate ferrous from non ferrous objects when using a mono coil. It does take time to master it but with experience one can even minimize digging ferrous junk while finding non ferrous items. Since you mentioned that most of your coins are low conductor then operating at normal ground balance and selecting low conductor should eliminate many if not most nails and other heavier ferrous items. What will be left will be the thin tin can type ferrous items. Generally, they will be a much stronger signal and wider, while non ferrous items will be a softer response.

It does take a while to fully grasp all the TDI does do when generating sounds by various metals. It isn't perfect, but it does work reasonably well.

Good luck and have fun. Keep us posted on how you do.

Reg

 

[AlexP]

Hi Reg,

Yes, the discrimination worked very well, especially with the 11" DD coil, no mater if the target was a nail or an iron coin. We also tried my friend's 15x12 DD Commander coil and I think the change in the pitch wasn't that obvious when passing that coil over ferrous targets. But it was a little less sensitive to very small nails. Very small nails weren't detected at all with that coil, which should be good for coin hunting.

I am not sure about the depth, but in the air it seemed to be about the same as with the standard 12" coil. Our soils are very highly mineralized. My Minelab Explorer SE picks up coins at just 4-6" in some places. If I can get twice that depth and have a reasonable discrimination with a DD coil, I will be happy. Next time I go out with my friend, I will do some depth tests with buried coins to compare both coils in real working conditions.

Right now, I am looking for an 11" DD Commander coil, but they are hard to find here. An alternative maybe would be the SEF coils for Minelab SD/GP/GPX. I am not sure how the discrimination will work with them, so will be happy to hear if someone tries one on the TDI.

As for the self-made coils, that's a good news. I will look for some web sites explaining how to build a coil and may have someone build one for me.

 

[prospector 55]

When you run the TDI for gold nuggett hunting and run it in the all postion it does disc out iron very well emitting a low tone on iron and a high pitch tone on a good target I have used this detector for about 8 months this guy really works like a champ and I HAVE DUG COUNTLES TARGETS TO POVE TO MY SELF THAT THE LOW TONE EMITTED WAS AN IRON TARGET the mono coil works very well and at very respectable depth two feet on a bobbie pin in mineralized soil, this machine still works better than any VLF around! there is alot of info from Whites on how to use this guy and from Steve Hersberg on another forum, I think you have to get a feel for the TDI to me it sounds just right for hunting down targets it is the way that it works it seems very natural to me compared to a VLF it is like it is an extention of what I am doing not like a foreign object in my hand, just keep on using your unit and trying different combinations of coils and settings you will eventually find some that work very well..
Happy hunting