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Pi ( TDI ) Coin Detecting Advice Request


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I've been experiencing lower yields due to sites being detected, by me for sure and there are also signs by others previously.  SchoolofHardNox's success on a beach using the Minelab GPX 5000 reminded me to re-read Steve's treatise on using the (in his case original big box Pulsescan) TDI for coin detecting.

I just a few days ago stumbled upon a promising site where extra depth could be key.  It's a schoolyard going back at least to 1955.  Unfortunately as is the case in many of my public sites, it has a history of backfilling.  From aerial photos I see than in the 50's it was grass/sod covered but in the early 60's they put down gravel.  The person who told me about the site (a person who walked up to talk when he saw me hunting a nearby park) said he was a student there 45-50 years ago and at that time it was (again) grass/sod.  I did a one hour survey hunt with the Minelab Equinox (11" coil) and encountered a couple inch thick gravel layer about 5" down.  I did find one Wheatie below the gravel, but 7" is getting deep for my detector + soil mineralization combination so if coins remain from the 50's (pre- gravel layering) then I expect I will do better with extra depth (and that may even be required).

One thing I've found in my detecting of these older sites -- there are always nails present.  So even if my TDI/SPP can deliver in the coin category it's going to be signalling on a lot of nails.  One of the tricks Steve used was to set the conductivity switch to high conductors (low tones) but the TDI/SPP doesn't have that feature -- I will be hearing both high and low tones.  This is a dual disadvantage -- extra tones to have to mentally tune out but also extra threshold noise since both parts of the signal spectrum will be contributing to that as compared to only half when the conductivity-low switch selection is made (on all TDI's except the SPP version).

Here are some specific concerns:

1) Am I fooling myself thinking I can get extra depth with the TDI/SPP, particularly when it comes at the expense of a noisier threshold?

2) Which coil(s) should I be using (choices I'm considering are 6"x8" Nugget Finder Sadie mono, 7"x14" NF mono, and 12" round White's 'Aussie' mono)?

3) Should I flag the promising targets but double check with the Eqx 800 (and if so, should I use the 11" or 12"x15" coil on the 800)?  (Note, even if I choose this route I will likely at first dig, regardless of what the 800 says, just to get an idea of what is giving the signal and how deep the targets are.)

Any other advice (from anyone) is appreciated.

 

 

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From what I have read here and what others said you can ground balance on the iron so that tone is different than targets above that range. I don't know if that will be 100% is separating iron from non iron. Next thing you can do is use the pulse delay to trim out smaller targets.

Having only the Seahunter, depth gain is only greater where there is more mineralization when compared to an IB machine. In other words in mild ground you may see little or no difference when compared to your Nox.

Big draw back for my SeaHunter with the 10x14 coil comes when there are lots of targets that are within the coil size so separating out targets is nearly impossible. Low target density is not an issue.

Still templted to buy my buddies TDI Pro but would consider an eliptical coil with smaller footprint then it goes back to the question, how much depth will I actually gain?

Bottom line if your ground is nasty in the high 80's-90's then the pi should do better.

Sorry for the long non answer hehe.

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I'm not sure if this is the same reaction other PI's get, but on my GPX, coins hit louder and narrower than big nails do. Nails, for me, sound longer, and coins hit faster if that makes sense.  Coins are a shorter signal but ramp up and ramp down quicker.  Also coins sound the same no matter what direction I swing from. Nails can sound different from some angles. This for me has been true to about 9". After that coins are a smooth quieter sound while iron is a bit ragged and unsure and sharp. I can always get a nice sweet, quiet, even response on deep coins. Deep iron sounds unsure and iffy. Kind of like when you want to make a bad signal into a good signal. That works up to about 15" After that all bets are off. After 15" it may sound like ground noise, slight EMI, or kind of a wavy, distant ghost sounding signal. After 20" I just hear threshold 😄

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GB :  I know there are some coin/relic guys who will try to use those balls-to-the-walls pulse machines , for coins/relics.  Since, sure, you can "get a coin to 1.5 ft. deep", blah blah.  I saw a few of them guys at the Virginia relic shootout a few years ago.  And asked them "Don't nails give you fits ?"   They only gave rambling feeble replies.

 

Lo & behold, at a few cellar-home antebellum home sites (which were a THICK carpet of nails), those guys were nowhere to be found.   They steered FAR from any such area.  Meanwhile, guys with standard machines (discriminators) were able to go fish some coins and relics from the mess.

 

So I can't see the sense.   Unless you're nugget hunting, or hunting the beach (where you're not likely to have ghost-townsy-conditions ), or some such exception.  

 

And as far as what kac says:  Yes there's some "tricks" you can use to ID nails of some of those type machines.  But guess what ?  The moment you off-tune and start using those tricks, you can now kiss that fabled depth goodbye.  You are left with no-more depth than a standard coin machine. So why bother ?   Any iron-ID trick on those will only work for the top 6 or 8" or whatever (at best) .  Everything beyond that starts to sound the same.  

 

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5 hours ago, kac said:

Next thing you can do is use the pulse delay to trim out smaller targets.

That's the other thing the TDI/SPP doesn't have that the TDI/SL does -- adjustable delay.  On the SPP it's fixed at 10 microseconds (nominally -- the minimum value that the SL will operate at).  Steve's recommendation in the treatise I linked says minimum delay worked best for him, so I'm counting on 10 us not being a problem....

5 hours ago, kac said:

Bottom line if your ground is nasty in the high 80's-90's then the pi should do better.

My ground is moderate in mineralization (2-3 bars on the Fisher F75 and Gold Bug).  So there is some loss of depth with an IB/VLF (and/or loss of accurate TID with depth) but nothing like happens at some locations.

1 hour ago, schoolofhardNox said:

That works up to about 15" After that all bets are off.

The TDI/SPP doesn't draw as much current as the GPX so I won't be able to get as deep as a GPX, but if I could get to 12 inches for a dime I expect it will do really well in a couple of my sites, including this one.  Heck, even 10" if broad enough over the coil footprint would be better than I've done with the Eqx & 11" coil.  Maybe I should try the Eqx with 12"x15" coil first and see if it finds anything deeper.  I expect to have lots of time this year to detect this site and it's not huge (maybe 60 m X 80 m).

 

18 minutes ago, Tom_in_CA said:

(I) asked them "Don't nails give you fits ?"   They only gave rambling feeble replies.

Well, that is likely a limiting factor.  I don't recall too many iron hits on my first pass over this site.  But maybe my brain was just tuning them out, and I was using earbuds which make it harder to hear the faint iron compared to using the over-ear headphones (Sunray Pro Golds in my case).

Thanks to all three of you for your replies.  I think I'll just have to try it out and see what I find.  It will probably be obvious pretty quickly if this has a chance of producing the deep targets I'm hoping for.  Either way another lesson will be learned.

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If you only have a 2-3 bars on your ground phase then depth is probably similar to your nox. Why not snag a nice old fashioned analog machine for those sites? Tejon will give a flat tone and most often a little pop on aluminum so it makes going through moderate and low trash areas a breeze. I say that because the machine is just not chattery as my vid machines. I can crank the sensitivity to nearly max and have clean signals. In rare cases where there is high trash areas the modern machines can squeak out a signal with the faster recovery speeds. The Vista X is supposed to be close to the tejon with the benefit of iron audio. Sometimes its just nice to think less.

As for headphones with an analog machine you really need good ones. Garrett MS-2's or Gray Ghosts etc. Earbuds you won't hear the nuances.

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2 hours ago, schoolofhardNox said:

I'm not sure if this is the same reaction other PI's get, but on my GPX, coins hit louder and narrower than big nails do. Nails, for me, sound longer, and coins hit faster if that makes sense.  Coins are a shorter signal but ramp up and ramp down quicker.  Also coins sound the same no matter what direction I swing from. Nails can sound different from some angles. This for me has been true to about 9". After that coins are a smooth quieter sound while iron is a bit ragged and unsure and sharp. I can always get a nice sweet, quiet, even response on deep coins. Deep iron sounds unsure and iffy. Kind of like when you want to make a bad signal into a good signal. That works up to about 15" After that all bets are off. After 15" it may sound like ground noise, slight EMI, or kind of a wavy, distant ghost sounding signal. After 20" I just hear threshold 😄

The SeaHunter you can sort of tell iron from non iron as the signal is a bit louder and slightly different but if I use the regular waterproof headphones I can't tell. Other problem is it has a mono coil so multiple targets are really tough to pick through. I use it on the regular beaches along the water line or in local swim holes that don't have a lot of trash. Areas I want to use it is in the old river here to bust through the bog iron but we have power lines on either side that drive it crazy. One the reasons I wanted the TDI was for the river banks but think EMI will be a problem for that as well.

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Quote "From aerial photos I see than in the 50's it was grass/sod covered but in the early 60's they put down gravel.  The person who told me about the site (a person who walked up to talk when he saw me hunting a nearby park) said he was a student there 45-50 years ago and at that time it was (again) grass/sod.  I did a one hour survey hunt with the Minelab Equinox (11" coil) and encountered a couple inch thick gravel layer about 5" down.  I did find one Wheatie below the gravel, but 7" is getting deep for my detector + soil mineralization combination"

I think the best option for depth and mineralization is to go for a larger coil size, but for me the gravel would be my concern as far as digging goes. As stated by others VLF is a better choice with a lower frequency design or option. They go deep and can discriminate saving a lot of holes that need to be dug. As the land is rezoned leaving no trace is less required.

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Hey GBA, 

As I've posted about, I have a similar site that I am hunting.  Old ground (early 1900's), lower yields due to massive detection over the years, over fill (old coins recovered at Depth with a capital D - 10 -11").  I have attempted the PI run a few times, but discovered I need to work more at clearing the upper layer of trash before attempting it again. 

No question in my mind that the PI will go deeper than my coin machines, but it does find every small bit and bob in the soil... so be ready to dig.  There was an incredible post by Tom D. on his site years back, talking about clearing a turf site with a pi machine, and his finds... it was fascinating and worth a read if you haven't already.  I am about ready to take another run at my site with the ATX after spending some time with other machines clearing trash.  

When I fire up the ATX on the turf, I'm not thinking about conventional discrimination - even though the ATX does have the ferrous/non-ferrous tones (it is only accurate to a certain depth, which is actually above the layer I'm trying to punch down into) , so really what I try to do is set the sensitivity where the 12" target will give me a faint signal... and I use that to "manually discriminate" the digs.  I don't mind digging iron... when I'm in the mood for digging iron... so I need to be in the mood for the ATX on the turf.  I may be in the mood again soon.  I'll post my finds.

I don't know the TDI too well, but speaking strictly PI, I think there is a place for it if you are up to a long day with maybe a good find or two.  I am interested to hear how you do at your old site (both with the large coil on the EQX and with the TDI if you decide to give it a go).    

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I too think the gravel layers are going to cause havoc for the VLF/ Multi's. Kind of like disturbed ground did on my E trac and CTX.  I would pick a small area and go over it with the large EQ coil, then go over it with the Tdi and see how many targets it can hear (without digging them all). That will tell you everything you need to know about conditions. Cherry pick certain signals and see how it goes.

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