Nulling in bad ground...Technical question

[Anonymous]

Here's one for Cody or anyone else who may be able to help. I have been using my XS for 3 years and twice now this condition has come up, the latest being this weekend. In certain large parts of ground my sweeps would completly null out except at the end of my sweep. When I would move say around 20 feet away it wouldnt be as bad. Then another 20 feet it would completly null out again. Im thinking it was bad soil, highly mineralized. I would still get a few signals but dug nothing deeper than 4 inches. I know there should be much deeper coins there as I have dug coins at 10 inches at this site.
First question: Is the nulling out masking deeper coins? And second: Is there anything I can do with the settings to overcome this condition? I did fool around with the sensitivity and that did not help. I did not fool around with iron mask. Maybe I should have but it was frustrating so I moved on to other productive areas. Sure hope someone has a suggestion because it sure could mean reaching the deep old silver that I'm sure is there.
Thanks,
Marc

 

[Anonymous]

Nulling is caused when the signal tries to hit in the blackened portion of your screen. You must be going over a large area with lots of nails or high mineralization which is causing it to try to hit in the blacked out area. Yes, that nulling out may be masking deeper coins.
First, I would try IM at -16, just to see what's there. At IM-16 there shouldn't be any silence. Either background hum or target noise. The target noise will likely be a buzzing due to the iron if you're running ferrous sounds.
Then, if you hear higher pitched targets mixed in with the iron sounds, you're onto some coins possibly. When the detector blanks the sound because it hit in the blackened areas, it waits a small amount of time before it either recovers to the threshold hum or reports another target. If that other target is also in the black zone, it continues to blank the sound and waits again. IM-16 lets all of the sounds through.
If hearing all the sounds still drives you nuts, try using Fast recovery, and swing a lot slower.
Good Luck, and let us know what you find!
- Rhoderman

 

[Anonymous]

Marc,
Threshold null discrimination will null just as you describe when there is a geological area that is very different from the other soil in the area. The sound at the end of the sweep is very common in those areas and is mostly due to the arch of the coil at the ends of the sweep. Since the soil is highly mineralized even a slight tilt will cause what use to be called "overshoot". This is a common problem for any VLF. I agree with your assessments completely in that most likely it is highly mineralized soil unless there is a lot of fill dirt. Fill soil is often very different than the soil common to the area where the fill has been dumped so will also causes this problem.
Question #1 Does null decrease depth or mask deep coins?
Yes, null does mask deeper coins to some extent. That area of the soil is in effect a large rejected target. Ground balance is actually ground discrimination. It would be difficult to detect a deep target because the circuits are being told to reject that large target, the soil, so is similar to a large co-located iron target next to a coin. Many VLF detector have circuitry to try and keep the null from going too negative such as in a silent threshold design. However, it does cause a loss of depth if you go over a good target while in null.
Question #2 Is there anything I can do with the setting to overcome this condition?
Yes, <span style="background-color:#ffff00;">iron mask at

 

[Anonymous]

Rhoderman, I just looked at your suggestions to see how we compare. You have some pretty tough ground to deal with in your area and it looks like you have an excellent understanding of the Explorer and experience with the detector.
Do you use the small coil and stock coil and if so how much difference do you notice in the way they respond to external noise, stray RF and hot soil?
HH, Cody

 

[Anonymous]

Everything cody said plus you might try audio 1-3 instead of the default, I hear it grabs on to a target and holds on longer so if you creep over a coin and it gets a lock it might be enough to get your attention verses just a peep.
I don't like fast on, it might work but the machine is less accurate in its assessment of the target with fast on, it has less information to work with and if its already reading a huge mineralization target I would think the longer the explorer has to see a coin mixed in that mess the better but thats only a theory. I'd try it both ways.
One thing for sure, when you think you might have found a target, before you dig it try a lot of different settings and see which combination works best, then run those for a while and if you find another do it again. Thats probably the best way to figure out what setup will work best in that soil.
I also agree with the gain, some sites I hunt just absolutely hate the gain any higher than 7, I get so many false high signals I could not hear a deep silver mixed in that noise as they sound about the same.

 

[Anonymous]

Out in Oregon they have a lot of heavy black sand, it was tough to get any depth at all and I was running wide open IM -16 with my sens manual at 25 with the machine sort of stable. I got pretty irritated to the point that I tore off my coil cover (black sand and water between coil and cover is a bad thing), cranked the sens to 32, it was noisy and unstable as all get out but it did lock onto several wheats and a couple silvers around this statue I had already hunted. Trouble is I could only hunt that way for about 30 minutes before my ears gave out.

 

[Anonymous]

While hunting in the orange dirt of Virginia and other states, I found that using Auto Sensitivity actually helped getting depth in that nasty dirt... If you havent tried that yet....
Its the only time I use auto when the ground is just plain bad, and its not iron causing the nulling...
Opening it up to iron mask -16 isnt a bad way to see how bad the ground is either..
One thing for sure you need to hunt slow in a null... By the way I was getting minnies at 8 to 10 inches in that orange dirt in auto, but was having trouble getting them at 4 in manual

 

[Anonymous]

Cody wrote:
<span style="background-color:#ffff00;">The electronic footprint of the stock coil will see about 5 gallons of soil at any given point in time. The small coil will cut that volume down so the cirucits can more easily deal with the high minerals. </span>
If one lives in Canada there's just no way a Minelab can see about 5 gallons of soil because they use litres over there!
Canadians Minelabs can see only about 19 litres of soil whereas (and this gets tricky) Minelab users in the U.K., since they are under the Metric system, their Minelabs see only about 4.18 metric gallons to our 5.02 gallons.
So you see, Cody, I am an expert on this and you should have conferred that PhD. on me and not C.C.

 

[Anonymous]

Jim, great suggestions. The only time I have seen semi-auto do poorly is in the house where there is a lot of RF that kicks the sensitivity down or at a site where there is strong RF to kick it down. I also use semi-auto for mini and round ball hunting and see the same depths.
You can work a little slower in manual if the threshold stays solid because you remove the semi-auto adjustment feature. Most of the sites I search will not keep a solid threshold in manual due to ground noise and stray RF. On tests where there are no stray RF, semi-auto will detect a quaret at 8 inches with the sensitivity all the way down to 1 while in manual it will not detect the quarter at less than 16 in the specific soil I used for the test. The key to semi-auto is to increase the audio gain to a higher level than 5 or 6.
Semi-auto will set the SNR, signal to noise ratio, and maintain the best for the area searched. I see great deth with Semi-auto in conjunction with the audio gain between 8 to 10 and the small coil. This setup is the best I have seen in trashy ground of all the machines I have used.
HH, Cody

 

[Anonymous]

Marc,
Here is a picture of some of the soil that I detect in at some sites around this part of the world(I borrowed this picture from the P.I. forum. It was posted by a local named Tony who also hunts the beahes in this part of the world with P.I. technology.
It is what we call pea gravel. If you put a magnet to it they will stick. Therefore it must have a ferrous content.And sometimes this stiff stciks to and iron object so it is sometimes magnetic. There are areas that are basically made up of this stuff and the red dirt that surrounds it, which it to is magnetic and/or rather attracted to a magnet.
There are sites that had bricks and this stuff that had a mixture of coke, fly ash and these stones mixed with the red clay to form bricks back in the days of early Europaen settement up to about 40 years when they stoped using such mixtures for housing bricks.
Put a magnet to all of these bricks that litter some sites that were built 100 to 130 years ago and recently demolished(can't believe they did this but they did )at it will stick. I hunt these sites often with the Explorer XS and Explorer 11 and these will sound off on these bricks and gravel and even some of the other natural rocks and boulders on our beaches. So I adjust my detectors SENSATVITY to about 24 and switch to MANUAL and the problem is gone.
I have never had any of these materials cause nulling of the THRESHOLD on the EXPLORER, nor are they detectable as a LOW TONE IRON object in -16 IRONMASK. In fact they sound of high and show up as a very top right hand silver target BUT with a very thin and NOT as rounded solid repeatable sound that is more difined on a silver targets. Iv'e detected good targets through this stuff NO problem. So I guess the iron oxides have a limited effect on Explorer.
What DOES affect and claerly register on the Explorer,it seems, is MOSTLY the man made processed iron that is still yet to TOTALY oxidise. This, I have found is what will cause the THRESHOLD to null when it is passed under the coil. Saltwater dosen't do it. Bauxite and latertite laden soils around here dose'nt do it. So I ask what other sort of "mineralisation" does.
So I think that area you have passed over where the nulling of the THRESHHOLD ocurs is due to some manufactured iron.
Will the Explorer see a non ferrous target in an area where ther is a THRESHOLD null...YES, depends on whether the target is placed in relation to the coil and what coil is being use along with the the settings of the Explorer(refer to the settings suggested in previous psots to this one) . Let me assure you that if the iron mass is to big or the target is located in the wrong place you will not loacte it unless you firstly remove this mass( or small pieces lumped to gether from the site) Could be just about anything that is buried there. The other thing is that maybe the Explorer is NOT conventional VLF technology as previuosley suggested it might be. This is pobably why it is such a versatile KIKASS detector.
Hope this helps.
Hard Nosed

 

[Anonymous]

Marc,
I'm in Charlottesville & have had the same problem; I'm looking forward to giving some of these responses a try.
Where are you?

 

[Anonymous]

and, i found that a coin pattern works best in this null area.
with the IM opened up, i can't even tell some of my test coins are there.

 

[Anonymous]

I find my yard and some of the areas I hunt are pretty much the same no matter what the coil. I mainly use the WOT for large areas since I swing slow.
If I were going for the best depth I would probably use the stock coil as it has found most of the deeper targets for me. The 8" ML coil seems way too small for me, and it still has plenty of problems. The WOT seems fairly stable at around 20 sens. I can run the 10" ML coil at around 25, and pretty much max out the 8" on sens. I have the best results in my coin garden with the 10" stock coil.
What are your observations as to coil size and performance?
HH - Rhoderman

 

[Anonymous]

There are two primary reasons why I will use a smaller coil. One is problems from co-located targets in heavy trash. The electromagnetic footprint of the stock coil is about the size of a trash can lid. We all see this when we have iron that masks targets. I dig up trash iron targets and was at first amazed at how much was being masked. I have found many good coins after removing a crushed soda can or other large piece of trash metal. I also can run the audio gain and sensitivity much higher and have fewer problems with stray RF and ground noise and keep the detector's threshold solid.
However, it is the stock coil that gets that extra depth. As you know a little more depth can make a tremendous difference at an old site. So it is pretty much the small coil for trash and the stock coil for cleaner ground as a rule of thumb for me.
I have found the deepest coins and relics with an Explorer and Sovereign. I measured the length of the digging tool I use can get some idea of depth. The vast majority of coins and rings I have found that are in the 1800 to early 1900 - 1920 or so are almost right at 5.5 to 6.5". In Nebraska they were more in the 6 to 8" range. I have not often seen many coins deeper than 8 to 10" in all these years of detecting. I have found some at 12 to 13' but not many. Relics seem to go all the way down to 1.5 to 3 2.5 feet.
However, 6 to 7" are magic numbers for the small and stock coils for me. If I could go to a larger coil then I would expect to get more depth but find it difficult at my age to horse one around. <span style="background-color:#ffff00;">At this point in time I am a strong believer that we get enough depht but need to have discrimination at depth. Also, to be able to ID aluminum from precious metals and rings from tabs. </span>
I have not used the WOT but here a lot great reports on this coil.
HH, Cody

 

[Anonymous]

The more noise and false signals, the faster the brain goes to sleep and day dreams!

 

[Anonymous]

I have found many silver coins with iron rust on them from sitting on or under iron but one stands out in particular that I found a couple of years ago. I was hunting an old school site finding a few nice ones and got this nice silver tone hit with the cursor buried in the upper LEFT corner. Of course I thought it was iron (which it turned out to be) BUT I was getting such a nice pinpoint and silver sound that I decided to dig it any way. Turned out to be a 40's Merc about 6 inches down. The was NO rust on the coin. When I removed the coin the iron signal was still there but it didn't sound the same. Still locked in the upper left corner. Only happened once so far but it was one to remember....

 

[Anonymous]

It was under a bolt. Try finding a rusty coin with another brand. lol

 

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