coins giving an "iron" reponse

[mojotrout]

When I swing over my 8 inch clad quarter in the year-old coin garden, I get a consistent iron grunt. This does not occur on a 6 inch dime (clad or silver). This has me a bit worried. Ive read Digger's idea about how iron can sound like silver because of "wrap around" but I didnt think about it working the other way around = silver sounding like iron. Now Im wondering how many deep coins I walked away from because the 705 was giving me a solid iron tone. I can handle digging for a coin that turns out to be iron, but having the machine tell me its iron when its really silver is unacceptable, especially when its a multi-toned.

Has anyone else had this experience and is there anything one can do with the settings to avoid this? And what about depth--how deep does an item need to be to fool the 705 into thinking its iron? for me its somewhere between 6.1 and 8 inches.

I dont want to have to start digging everything that is over 6 inches deep and gives a clean iron grunt. Any help would be appreciated!

 

[Dirt Hound]

you say at the beginning of the post "clad quarter". later in the post you talk about missing silver because of an iron grunt -- which is it? I could not ever imagine silver giving an iron grunt... clad, I could understand, though. Canadian clad at least, give a terrible response on the 705.... which doesn't bother me, because I'm not looking for clad

 

[mojotrout]

sorry, it is a clad quarter in my garden. But on my machine silver and clad give similar tone response and often similar numbers too, so i am worried about passing silver by in the field. If silver wont iron grunt when deep, them Im not that worried--I have no desire to dig 8 inches for a clad quarter!

 

[Dirt Hound]

Ya... I wouldn't worry about silver giving an iron grunt Also, do yourself a favor and upgrade to the 10.5" 7.5khz DD! Awesome coil.

 

[mojotrout]

youre the third guy who suggested the 10.5 7.5kHz coil! How much more depth than the 9 in 7.5 concentric?

 

[Dirt Hound]

Honestly, I've never bench tested or anything... but I've dug coppers in the 9-10 inch range. I'd say it's definitely deeper than the concentric, plus the added bonus of better ground coverage. Honestly, I had a hard time choosing to use the 705 over my old Teknetics Gamma (with a 13" DD) when I had the concentric on it. It wasn't until using the 10.5" DD that I really got confident in the machine, and started to love it Now I couldn't imagine using anything else!

 

[bleeohio]

The 10in dd coil in mid freq. Turns the xterras into a deep coin vacuum. I wouldn't coinshoot on grass without it.

 

[glabelle]

Well, it's funny you've seen this too. I just today, received my 705. My intention was to get a machine exclusively for deep silver dimes and wheaties.
I know the eTracs/explorers are known as the best for this, but I've had 'em and didn't like 'em (V3i too). I was hoping the 705 with 3KHz coils would be *the* machine.

My initial tests are inconclusive. I have a silver dime buried at 5" in my test garden which is moderately mineralized to make it tough and mimic the soil here in Oregon. It is "Play Sand" from Lowes.

My MXT Pro hits it fairly well with an SEF 8x6 coil (DD), pretty iffy with the Eclipse 5.3 coil (concentric). My old Classic III with Mr. Bill's mods hits it fairly well, and smooth, with a Bullseye 5.3" coil (concentric). I attribute this to the mineralization and the abilities of the 6.59 vs 14KHz frequency. I hoped the 3KHz machine would be even better.

The 705 with a 6" Digger coil (DD) would miss this dime! I get "iron" tones (no ID) also when passing over this coin. If I go real slow, there is an occasional good hit, and it IDs ~46, but if I didn't know the coin was there, I'd get a negative hit tone hit, and no ID and not dig it. The standard 9" concentric, 7.5KHz coil hits the dime fairly well, so this is encouraging.

I have a 10x5" 18KHz and 9" 3KHz concentric on the way. Hopefully the 9" 3KHz concentric will pan out.

George

 

[Mark in S.E. IA]

mojo, when you made your test garden did you first check the area for any signals in AM. If you didn't then their might be a nail or some other piece of iron close to the clad quarter.....

Something to keep in mind when your MDing at a public park or old school. Most of the good signals have already been dug by ppl that have MDed it in the past. The old coins that are still there are being masked by something and most times it's a nail or a rusty bottle cap. When in farm fields it is really common to get a iron grunt along with coin tones. Their is a lot of iron at those old farm houses and 1RSH's.

I've been using the 10.5 MF DD coil for 7 years now and that's the only coil I use but my ground a round here is a lil on the hot side and the DD type coils work better in that type of soil and it gets GREAT depth. I've dug seated and barber dimes and also IH's at 12".

 

[Old Longhair]

Before I make any suggestions, I want to know more.

AM or C/T Mode?
What's the Sensitivity set at?
Auto GB or manual?
Tracking ON or Off?
Any Offset?
What ground phase number did you wind up with?

 

[Billium]

Mojo,
I might be able to help in person. Message sent.

 

[mojotrout]

Hi OLH, settings are as follows:

AM 99 tones
Sensitivity at 25 (can actually go to 30 w/o chatter)
GB tracking on (but manually GB'd first)
No offset
Phase = 28
9 inch 7.5 kHz coil
Noise reduction = +1

I removed all the iron I could find, but you never find everything so maybe some bits and pieces remain here and there. Its not a real trashy part of my yard. My other machines never picked up an iron signal over the quarter, but be to be honest, I dont recall them getting much of any signal over the quarter.

The machine hits an 8 inch rusty nail I have buried louder and crisper than the quarter but with the same tone and the -8 TID.

 

[mojotrout]

Looks like Jabbo is getting grunts on silver too (although his was an indoor test). That makes three of us. Maybe we can find the common thread between our experiences and figure this out.

 

[Old Longhair]

OK. The first thing that I would suggest is that you actually measure the ground minerals per the method outlined by BarnacleBill (found in the FAQFAQ pinned thread) to see whether you're dealing with magnetic or conductive minerals. You're right at the cusp of where a DD coil might make a notable difference due to the total volume of soil within the detection field containing content that the machine has to compensate for.

 

[glabelle]

Do not fear, there is a fix!

I suspected a "wrap around" type of an effect. However no amount of ground balance tweeking, even in manual would help.
I was comparing machines (MXT, Classic III, and X-terra) today on the 5" dime in moderately mineralized soil.
In this case all detectors were using effectively the same coil. 950s on the Whites machines and the 9" 7.5Khz on the X-terra.

Notably, in prospect mode, the X-terra detected the dime OK. Also in all metal or pinpoint, even IDing it correctly!
Then I noticed the +48 notch in the C&J mode, obsensibly to knock out hot rocks. But, don't forget, there is a shifting upwards of a weak target's phase due to mineralization.
I removed the +48 notch on "Pattern #1" and BINGO! Dime detected rather easily. (Not quite as good as the Classic at 6.59KHz)

I'm hoping for big things when I receive my 9" 3KHz coil!

Oh, since my primary goal is a "silver dime machine", I notched out everything from zinc penny and below, and there was no apparent loss of sensitivity to the dime.

George

 

[mojotrout]

thanks George. I will give that a try. I wonder if having that notched out messes with hearing the tone changes when coins are near iron when in the 99 tone setting.

Also, OLH-- I read BarnacleBill's post on getting a read of the ground minerials and he mentioned starting a database for mineralization readings with the X70/705. Do you know if that was created? I will be checking mine--at least the ground in my back yard-- and wanted to know what type of info the database was keeping.

I'll let you know what readings I get tomorrow when I run the test.

 

[Old Longhair]

His idea for a database never materialized.
Most of us that utilize his measuring method don't even write it down. We just use it to know what we're up against at certain sites that are known to be trouble, as it can be used to possibly make a coil/frequency decision.

 

[Neil]

When I swing over my 8 inch clad quarter in the year-old coin garden, I get a consistent iron grunt. This does not occur on a 6 inch dime (clad or silver). This has me a bit worried. Ive read Digger's idea about how iron can sound like silver because of "wrap around" but I didnt think about it working the other way around = silver sounding like iron. Now Im wondering how many deep coins I walked away from because the 705 was giving me a solid iron tone. I can handle digging for a coin that turns out to be iron, but having the machine tell me its iron when its really silver is unacceptable, especially when its a multi-toned.

Has anyone else had this experience and is there anything one can do with the settings to avoid this? And what about depth--how deep does an item need to be to fool the 705 into thinking its iron? for me its somewhere between 6.1 and 8 inches.

I dont want to have to start digging everything that is over 6 inches deep and gives a clean iron grunt. Any help would be appreciated!

Mojo Ive not seen this on my 705 yet but its not unique to the Xterra as Ive seen it happen on CZs and Sovs also, coin targets/rings at fringe depth can give an iron signal.

 

[atomicscott]

Do not fear, there is a fix!

I suspected a "wrap around" type of an effect. However no amount of ground balance tweeking, even in manual would help.
I was comparing machines (MXT, Classic III, and X-terra) today on the 5" dime in moderately mineralized soil.
In this case all detectors were using effectively the same coil. 950s on the Whites machines and the 9" 7.5Khz on the X-terra.

Notably, in prospect mode, the X-terra detected the dime OK. Also in all metal or pinpoint, even IDing it correctly!
Then I noticed the +48 notch in the C&J mode, obsensibly to knock out hot rocks. But, don't forget, there is a shifting upwards of a weak target's phase due to mineralization.
I removed the +48 notch on "Pattern #1" and BINGO! Dime detected rather easily. (Not quite as good as the Classic at 6.59KHz)

I'm hoping for big things when I receive my 9" 3KHz coil!

Oh, since my primary goal is a "silver dime machine", I notched out everything from zinc penny and below, and there was no apparent loss of sensitivity to the dime.

George

I believe (correct me if I'm wrong, mojo) Mojo is running all metal/wide open, so opening up the 48 notch wouldn't apply here. I never have had this prob with my 505, I only use the 6" dd HF coil though.

 

[mojotrout]

I hate to make a post like this but it needs to be out there--

ok, so I collected some more data and here is the conclusion to this mystery -- Minelab X-Terras give an iron signal on deep silver or clad targets, at least they do when in moderately minerialized soil.

We had three X-terra 705s, two on my coin garden and one on another in a neighboring state. GB numbers ranged from 11 to 28. We tested five coils-- the 9". 7.5 kHz concentric, the 10.5" 7.5 kHz DD, the 6" 3 kHz (two different ones), the 9" 3 kHz concentric, and the 10x5 18.75 kHz elliptical. All of them gave an iron grunt on either an 8 inch clad quarter or a 6 1/2 in. silver dime. the Diggers could not find the 8 inch qtr. .

We tried them with tracking on and off, with manual and auto GB, with high and low sensitivity, in AM and with Disc (no signal at all once 48 and the iron TIDs notched, at least for the 10.5 DD and the 9 CC coils). The soil was fairly moist -- recent rain and/or lawn watered within 48 hours of test.

The one thing we did not check (at least the two of us on my garden) is the mineralization test. however, it doesnt really matter (to us who hunt here) what the results are on that if none of the coils will give a proper ID. If I can remember I will do that test and post the results so folks know what kinds of soil conditions we are getting these responses in. That said, the experts around SW Idaho claim this is not really minerialized soil we have here, especially in people's yards in town.

That's a pretty extensive test IMO. Three users, five coils, two sites, and consistent results. What it tells me is if you are in similar soil conditions as SW Idaho and you think you have a deep target (> 6 inches) and its giving you an iron tone, you need to dig it because it very well might be a silver coin. That's very unfortunate. I cant even being to count the times Ive walked away from an iron tone that showed 4-6 inches or more in depth. Big bummer for the 705 as a deep silver seeker.

This post isnt to start a fight, just reporting our real-world, honest to God results that I think folks should be aware of. Im not saying I dont like this machine anymore --its still a very versatile detector-- but I now see its limitations as a coinshooting tool. As always, your results may vary.