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GB_Amateur

Dealing With X-Terra Wrap-around

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This is primarily a coin and jewelry hunting topic, I think.  Getting more experience with different detectors, I'm wondering if I'm seeing a common (but hopefully not guaranteed) issue.  What I'm referring to is called 'wrap-around' and I'm sure it has other names.  Basically the low end of the induction balance (IB) ID scale is low conductivity iron and high end is pure silver.  But sometimes with iron you get a high ID, usually in conjunction with the low ID.  I've had this happen on three detectors but don't remember it on a 4th.  The three are:  White's DFX-300 w/ 950 concentric coil (least experience), Teknetics Gamma 6000 w/ egg-shaped conc. coil (intermediate experience), and Minelab X-Terra 705 w/ both 7.5 kHz 8.5" round conc. stock coil and Coiltek 3.0 kHz 6" round DD "Digger".  I don't remember this problem with my Gold Bug Pro with any coil.  I go into detail here with the 705 because I've used it the most in iron infested sites.

The lowest ID on the 705 is -8 and the highest is 48.  (All even numbers except 0 in between occur but never odd numbers -- by design.)  Iron is anything below 0; high conductive coins (Cu and Ag alloys) are above 35 (usually) with silver dollar being highest US coin at 46.  (Don't know what a pure silver round would read, maybe 48, but who drops those?? :smile:)  In the US Midwest we mostly have moderately low iron content (at least compared to US West) -- may be exceptions in iron mining areas like Minnesota and Michigan Upper Peninsula.  I've seen phase auto at 35 with the 7.5kHz coil and 8 or 9 with 3 kHz "Digger" (don't know why the disparity...).  I run max tones (~30 of them?) in "Coin and Jewelry" discriminate and alternate between "all metal" and notching Off below 0 and also notching Off 48.  Note: this detector has a prospect mode but that operates quite differently and I haven't used it for hunting coins, although I see that some have.

Even with the notching described above I get 46's and even 44's on iron targets.  In all metal I can hear the jumping between iron ID's and high conductive ID's, but this can (and does!) happen when you're going over a coin near a nail, for example.  The hope was that I could listen to tones and not have to look at the screen, but that doesn't seem to work well for me in the iron infested parks I hunt.  I'm sure with more experience (and, yes, I've read Randy Horton's "Understanding the X-Terra" multiple times) I'll get better, but I still find myself, even in max tones, having to look down at the screen way more than I would like.

So I guess I have a two part question:  1) is this an inherent problem in all coin hunting and multipurpose IB detectors, and if not, which ones are immune to it?  2) Do you have tricks, besides over-notching, to work around this problem?  I've found enough old coins that I don't want to notch out halves (ID=44), because I know, although rare, they are out there.  Lastly, I'm not interested in modern coins, although those come with the territory.  So far I've found old coins at shallow depths (4 inches or less) and none deeper, although I'm sure they are there.  I dig lots of pulltabs (square but mostly ring & beavertails) and don't mind that.  There are coins in that zone and I'm willing to put up with the Al in order to find them.

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Until someone smarter than me chimes in to help you out I would say that wrap around seems to increase with sensitivity.  My CTX 3030 does it real bad when you pump up the power.   I haven't experienced it much on my X-Terra although I haven't used it much.  I would say make sure your ground balanced. You might have to use manual instead of tracking and maybe try slowing down your sweep speed and cut back the sensitivity a bit.  I run the X-Terra in AM mode and don't notch anything. I use Prospect mode to check the shape of the signal.  I have also run it opposite of that and search for deep sounding coin size signals in prospect mode and check the target in AM.  Visual ID on very deep coins can be all over the place and even the tones will turn to Iron tones at the very edge of detection. 

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Thanks, CF.  All sounds like good advice / things to try.

Regarding ground balancing, I've never run in tracking.  I always use Auto (known as "Grab" by some manufacturers).  Should I be using tracking?  Interestingly, yesterday with the 6" Digger coil it ground balanced at 34, very similar to what I previously have gotten with the stock (8" 7.5kHz round concentric).  So now I'm thinking my previous observation of GB at 9 was somehow erroneous, either misreading my detector or balancing over metal or ??

It would seem to me that turning down sensitivity lowers response to all metals -- those I want to dig and those I don't.  So if that reduces wrap-around at the cost of losing deep (good) signals, then maybe I should learn to live with the wrap-around?  I've done air testing with a gain of 15 (factory setting) and a gain of 24 and it's clear that (at least in air) depth of all metals increases with gain more/less the same (i.e. max detectable depth increase/decrease is same for desirable metals and undesirable ones).  I usually run gain=24 but yesterday I used gain=27 and didn't notice much difference than previous trips to the same (iron-infested) location.  OTOH, I didn't find much yesterday....  :sad:

One thing I wonder aloud about:  are some detectors configured to 'protect' the user by limiting gain, while others are distributed with the "we'll give you plenty of rope and you decide how not to hang yourself" principle?  An example of the latter *might* be the Fisher f75 (which I don't own nor have ever used, but read plenty about it) where you can use things like "boost process" and turn Digital Shielding Technology (D.S.T.) off to get maximum sensitivity at the expense of an increase/decrease in noise (and possibly annoyance/frustration).

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57 minutes ago, GB_Amateur said:

Thanks, CF.  All sounds like good advice / things to try.

Regarding ground balancing, I've never run in tracking.  I always use Auto (known as "Grab" by some manufacturers).  Should I be using tracking?  Interestingly, yesterday with the 6" Digger coil it ground balanced at 34, very similar to what I previously have gotten with the stock (8" 7.5kHz round concentric).  So now I'm thinking my previous observation of GB at 9 was somehow erroneous, either misreading my detector or balancing over metal or ??

It would seem to me that turning down sensitivity lowers response to all metals -- those I want to dig and those I don't.  So if that reduces wrap-around at the cost of losing deep (good) signals, then maybe I should learn to live with the wrap-around?  I've done air testing with a gain of 15 (factory setting) and a gain of 24 and it's clear that (at least in air) depth of all metals increases with gain more/less the same (i.e. max detectable depth increase/decrease is same for desirable metals and undesirable ones).  I usually run gain=24 but yesterday I used gain=27 and didn't notice much difference than previous trips to the same (iron-infested) location.  OTOH, I didn't find much yesterday....  :sad:

One thing I wonder aloud about:  are some detectors configured to 'protect' the user by limiting gain, while others are distributed with the "we'll give you plenty of rope and you decide how not to hang yourself" principle?  An example of the latter *might* be the Fisher f75 (which I don't own nor have ever used, but read plenty about it) where you can use things like "boost process" and turn Digital Shielding Technology (D.S.T.) off to get maximum sensitivity at the expense of an increase/decrease in noise (and possibly annoyance/frustration).

It sounds like something was off on your ground balance. Like you said you might of set it over metal. If you are going to use Manual you need to constantly check it to make sure the ground under you has not changed.  Try tracking to see if that runs better for you. 

You are also correct that you may have to learn to live with some extra noise to get real deep.  I only have about 10 hours or so on my X-Terra but was surprised how quiet it ran compared to my CTX 3030.  I was running the big 15" 3kHz Coil which is real deep on silver by the way and I didn't have much problem with wrap around or ground noise. I was running sensitivity around 26 and used both tracking and manual ground balance. If you can't get it to run quieter for you and the wrap around is driving you nuts you might notch out 48. I don't think you will lose out on anything by doing that. 

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First off, my thanks to Steve for setting up these new forums.

Adding to this thread, here are a few things I have seen with the X-Terra's which has ended up being a mini field test of sorts. LOL. 

Back before the original XT 70 was released I was fortunate to have an X-T 50 on loan to try out.  After receiving the new 70 and doing some comparisons, I found that the 70 was not seeing a target in iron that the 50 would signal on.  I rechecked the ground balance and still nothing!  Going back to something I remembered about the Fisher Coinstrike's iron handling I turned on tracking GB.  To my surprise the target was now clear and a full walk around signal!  I questioned one of the field testers about this and he confirmed that the auto tracking circuit has an iron filtering affect.  Why they do not give this information in the manual has always been a puzzlement to me as it is makes a huge difference.

A big complaint filed against the X-Terra's was and still is that they do not have the fast response of the competition.  While true to a degree, when setup properly they can do very well in iron filled sites.  Unlike some others you cannot run them wide open in iron, you have to throttle them back. 

A friend that was a Sovereign user often spoke of lowering the sensitivity to reduce nulling in iron for better iron see through.  This works with the X-terra's as well.  To do this chose one of the preset patterns and accept in all iron notches then, noting which notch or notches the iron is hitting in reject them.   This will of course cause the threshold to null out on the rejected iron and allow you to find a sensitivity level that reduces the iron response for better see through.

The X-Terra's are in my opinion one of the better do it all machines out there. 

Tom

 

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Been a couple months since the last post on this thread.  In the meantime the weather has gone from unfriendly to detecting in my home region (Midwest) to springlike temps (but dry!) giving many of us several days to hunt.  Also, I've since read Tom D.'s exhaustive feedback to Makro/Nokta regarding the new Impact.  I can't speak for others, but there is a lot of info there that, IMO, applies to other detectors, not just the Impact, Racer2, and Fisher F75 which he uses for comparison.  If you haven't seen it, keep in mind it's not a quick read as it took me several sittings to reach the end.  Here's the link to the forum thread:

Back to the wraparound issue, I got a chance to try the Minelab 5 inch round DD 18.75 kHz coil this weekend (11 hours total) on the X-Terra 705 in my two standard locations (both municipal parks) where I've hunted a lot in the past 7 months with the Fisher Gold Bug Pro (5 inch round and 7x11 in^2, both DD's) and the 705 with its stock (for coins/jewelry) 8.5 inch round concentric and also the Coiltek 'Digger' 6 inch round DD 3 kHz loop.

Just for review, in both locations I've found old coins (Indian Head pennies) and 19th century military buttons.  One was previously an industrial site while the other was a farm with outbuildings prior to becoming muni parks.  In particular the former farmyard is loaded with iron bits, especially nails but also fencing, implement parts, steel cans, etc.  This one has driven me bonkers with wraparound from -8 (most ferrous) to 48 (highest conductor) and even down to 46 (large format dollar) and 44 (half dollar).

Most of my previous searching was done with the Coiltek 6 inch, but I do recall wraparound with the ML concentric as well.  To my surprise and relief, running with the ML 5 inch @18.75 kHz, even in the worst iron infested spots, resulted in very little wraparound!  There was just a bit but it was not only easy to recognize, but so infrequent that I wasn't being confused/overwhelmed.  Iron sounded iron and conductive sounded conductive.

We can all speculate on the reasons for the huge difference, but given that non-ferrous and ferrous lead to different performance at different frequencies, with associated compression and expansion of response TID regions, this is likely a big factor.  I ran at the same gains (23-25) and (for the most part) in the same ground balance phase settings (31-32) via auto ground balance (not tracking).  For most of the time I was able to run in coin&jewelry "all metal" (no notching) and with "99" tone setting.  Auto frequency shift (to minimize EMI) is almost always +1 in these two locations, independent of coil choice.  In no way am I able to compare max depth (still building my backyard test garden) but first impressions are that there isn't an obvious/significant difference in that part of the performance.

Next time out (won't be this weekend as there is still some typical February weather forecast) I'll try the stock 7.5 kHz 8.5 in. round concentric again and see if it is in-between in terms of wraparound issues.  I haven't had that one on except for a couple backyard tests (backyard is pretty iron free, by comparison) since I first got the detector in August.  That will add some more data to my growing notebook.

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The 705 is very powerful and in a lot of cases you just can't run it too high on sensitivity, back it off. I rarely run in coin mode on 99 tones. I just run it in four tones. If you are hunting in heavy iron infested areas it will help to put it on two tones. You will have improved speed to discern between iron and a good target next to each other. Also all my best coin targets had negative id's mixed with the appropriate good I'd. This is because there were nails next to every one of them. I will never pass up a signal that has both positive and negative I'd. You will also get this mixing of I'd numbers when you have a deep target and the 705 knows there is a good target but it is at the farthest point it can lock on but until you get the coil closer it cannot determine that it is a 100% good target. I.E. non-Ferris.

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