TDI SL Around Old Foundations?

[kac 637]

How good would the TDI SL work for sniffing out coins around old foundations that have a lot of iron but low to moderate aluminum? I have been looking at various coil and detector options out there for the vlfs whether a new machine or for the machines I have and have a feeling they aren't going do do anything significant performance wise.

Trouble is some of the old coins I suspect are in the areas are near foundations and where land was disturbed when the buildings were constructed. Conditions have heavy brush so a smaller coil is needed to sniff around and tons of iron that mask out even my little concentric. Smaller coils aren't going to hit the depths I want to get to 12"+ on small silver.

Aluminum that is there is fairly shallow and not a big deal. I dig all the ring tabs as they have the same signal and vdi as flying eagles here. Can's I can identify with my eardrums 🙂

[coinhunterseth 29]

PI's lack much in the way of iron disc, and the TDI has none at all, so that would be one of the worst possible locations to use one.

[Steve Herschbach 22,580]

The TDI actually does have the ability to discriminate iron, although to retain depth you have to choose between detecting non-ferrous low conductors plus small ferrous items, or non-ferrous high conductors plus large ferrous items. It is possible to tune a TDI to completely reject iron, but when set up like that it is basically no better than most VLF detectors for depth.

White's TDI Coin Settings

Iron Discrimination with a White's TDI

White's TDI For Coin Detecting

In general however I'd not recommend a PI for foundation type areas unless you really like "out-of-the-box" type detecting.

[kac 637]

I wouldn't expect it to reject all iron, my impression is I could reject the flat nails and rusty halos. Coins I am chasing are copper based and silver though could go back over and search for gold and nickel. The non motion and power of the coil for its size is appealing. When you do reject iron does iron still mask the other objects?

[Steve Herschbach 22,580]

4 hours ago, kac said:

When you do reject iron does iron still mask the other objects?

Yes.

[kac 637]

So no benefit of using a pi then. That saves me about a grand and a lot of digging.

Thanks.

[Steve Herschbach 22,580]

The selling point for PI is more depth in mineralized ground once you can’t find anything else good anymore with a VLF. If you have a great location where lots of finds were made, but a VLF no longer produces anything, then a PI can turn up more good finds. The price paid is minimal discrimination capability.

This is why virtually all serious gold prospectors and many relic hunters end up going PI. The VLF detectors eventually tap out completely and so to stay in the game you either go somewhere else or go PI.

The main thing is the targets have to be worth it. I dig trash all day long looking for just one gold nugget. I prefer PI detecting for beaches for the same reason. Many relic hunters feel the same way. But is it worth digging a ton of trash around a foundation for an Indian Head penny? Not for me. If I thought a gold coin was there however that might be a different deal.

[kac 637]

Was doing some iron tests with my seahunter and the larger coil. Had a medium iron nail raised about 4" next to larger and smaller with a dime in between and surprisingly Ithe disc on the SH seemed to cut out the iron with setting around 3. Could hear the dime about 7-8" up. I am guessing I will get better results in the real world as the Pi air tests are junk imo.

With the  same test I was able to pick up on the dime about 6-7" away with my ATP stock coil by setting the iron disc to just scratch out but still audible. I was able to squeeze out a beep.

The Tejon with 10x12 widescan struggled on the same test.

In the field I do pretty well with the Tejon but finding some of these beat up spots tricky to sift through. If I get a break in the weather I will do some scouting with the Pi and have a buddy tag along with his Nox800 to double over on targets. See if I am hitting more duds or not.

Too bad the SH doesn't have a gb. Lastly the stock 8" coil with discrim doesn't seem as effective. Not sure why the larger coil does better, maybe the there is too much gain on the smaller coil? Bugs me because last I tried the big coil I dug about 4lb of iron at the beach with the bigger coil because I had the disc at 0 assuming it really wasn't functional.

[RickUK 356]

In situations like you have described although i do own a TDI Pro with both small and large coils,the TDI would be in my mind the very last machine that i would use.If i wanted both supreme depth and also discrimination on high mineral content soil then my weapon of choice would be my Nexus MP with the small 6'' coil on it.

With the conditions that you have described ie trash and iron for the most part using a PI would be a waste of time in my opinion,it would drive me mental lol.But the depth request that you are also looking at is also another major problem as even with a larger coil on 12''+ targets is pushing it on small targets,this is why i love using my Nexus with the small coil on,when on clear pasture sites then i use one of my larger coils for extreme depth.

Its a tough request and finding a machine/coil combination that ticks all your needs will be greatly reduced,you can find a machine that can get the depth but then struggle with the iron etc,so perhaps try and clean the foundations out with a smaller coil or iron and non desirables first then possibly use a larger coil for the depth,no easy way around it unfortunately.