E-trac vs. Crap Soil: Todays Oddity

[Dave Rishar]

E-trac vs. Crap Soil: Today's Oddity

I know that I've whined before about the challenges presented by our local soil, but I encountered a real doozy today that I learned a few lessons from.

Today's hunt was on a school playfield. Early in the 20th century, the school had actually been located on this lot. It was torn down in the fifties and the new school was built on the adjacent lot. The old lot had seen a lot of grading and filling at some point, but without knowing where that fill dirt had come from, it was still worth taking a look.

After setting up the E-Trac, I began swinging and ran into problems right away - the thing would not shut up. I figured that the metal ball cage was giving me grief and moved away from it, only to realize that it was the soil again. I played with the sensitivity a bit and found that I could only go as high as 15 without it driving me nuts, although it wasn't what I'd call stable at that point. I wound up keeping it at 20 for as long as I could tolerate it, then dropping it down for a bit to give myself a break. The ground was loaded with hot spots (not rocks, but actual areas of dirt) that would trick the machine in both TTF and 4TC by ringing from 01-25 to 01-40, with the annoying habit of showing spurious 10-35 to 12-45 signals. Attempting to pinpoint these would usually result in an area of about a square foot that would give various indications, with the middle invariably reading as a stable 01-30 or 25-50. Once I'd dug a few holes to confirm that it was just the ground playing tricks on me, I ignored them as best as I could.

So, the weird target: 25-44 repeatable from two directions, about two inches down. It sounded good. Everything remained the same in pinpointing mode. Would you dig this? I would, for a few reasons - it won't take long, it sounds like it's at least worth digging, and I'd quickly learned not to trust the ferrous numbers around here. I'd never seen one that high that was worth digging but everything else checked out, and the conductive number looked good and the E-Trac is usually pretty close on these. I was also honestly curious about what the heck I was swinging over, so I dug it.

The result? A US penny just under the root mat, laying more or less flat. Not at all what I was expecting, and the first coin of any sort that I've recovered that had a ferrous reading anywhere near that high. Figuring that a nearby ferrous target was bleeding into it, I changed to quickmask and swept the hole again after I was done. I found no other signals in that area. The penny had done this all by itself.

I'm not sure what the moral to this story is. Our dirt is terrible here? Even a high end machine can be tricked? Weird things can happen? Dig all repeatable signals? This field sucks? Maybe all of those things. What I do know for sure is that a 25-44 penny is a new one for me.

 

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[Fletch88]

Just out of curiosity have you hunted this spot in Auto Sensitivity? Sounds like you've got a combination of things going against detecting in this spot.

 

[Iron Patch]

So does your Tesoro also have serious problems with that dirt?

 

[Jackalope]

by ringing from 01-25 to 01-40, with the annoying habit of showing spurious 10-35 to 12-45 signals

Sounds like iron (nails) at 35-45Fe (low) with wrap-around to 01Fe (high). Since the penny was at 25-44 there is likely disintegrating iron pieces in the soil too. Once the target is dug the iron is removed/mixed and won't respond or respond less strongly. You may find running Auto Sens a smoother bet with less falsing. You could also DISC the 01Fe area to silence the high nail chirps. Pinpointing in all-metal will be erratic, centering on whatever is strongest. But you can center in DISC mode as you narrow the sweep over the target.

 

[Dave Rishar]

Just out of curiosity have you hunted this spot in Auto Sensitivity? Sounds like you've got a combination of things going against detecting in this spot.

I'm finding that auto sensitivity is useless in this area, as it will usually set itself at 15 or lower. I start it at 20 and adjust it downward as necessary.

So does your Tesoro also have serious problems with that dirt?

It struggles with a lot of the dirt around here. I haven't tested it in this particular field, but I suspect that it would be pretty chatty.

Sounds like iron (nails) at 35-45Fe (low) with wrap-around to 01Fe (high). Since the penny was at 25-44 there is likely disintegrating iron pieces in the soil too. Once the target is dug the iron is removed/mixed and won't respond or respond less strongly.

It had to have been something like that. Having targets reading a few points higher on the ferrous scale than where they should is pretty common for me. (They also sometimes register a few points lower, interestingly enough.) Still, it was rather odd.

To be fair to the machine, I actually can get it to remain quiet up to 20 or so on the sensitivity, but only if I'm moving my coil at a speed that can be measured in inches per minute. I'm willing to slow down like this in the really awful areas. (Yes, it does get worse than what I've described.) However, to use that swing speed all the time would require me to spend literally a year's worth of weekends to cover one field and this simply isn't acceptable. Instead, I swing at a "normal" E-Trac speed (2-3 seconds per swing) and live with the resulting noise, slowing down to re-check signals that didn't sound like falses.

On this last hunt, I did eventually started running a decent amount of disc, but only because I'd basically given up and would have rather dug shallow clad than nothing at all. I really don't like running any more discrimination than is absolutely necessary to make a hunt possible. It seems to slow the machine down even more, and aggressive ferrous discrimination can sometimes cause disconcertingly long null periods in my area. It's a wonderful thing to hear after having my ears battered for an hour or two but I really don't like long nulls, as all I can think about is what I'm potentially missing. My girlfriend already demonstrated this to me when she found her first wheatie - a coin which I'd missed five minutes earlier because I'd nulled out on the nail next to it. It was only a wheatie and was just that one time, but that's the only time that I asked her to investigate one of my nulls. I shudder when I think about all of the other ones. In this particular case, it was either up the disc or break the detector in half over my knee and throw the two pieces in a volcano, so I opted for disc...but I didn't like doing it.

Thanks all for the advice.

 

[Fletch88]

Dave, 15-20 in auto isn't really bad, compared to a chatty machine in 20-25 in manual sens. I have better luck with a smooth machine than constant chatter. I've heard if Etrac users using auto that goes down to 8-10 and get better depth than trying to run manual.

 

[Dave Rishar]

Agreed. It's far quieter in auto, although hardly silent. The problem is that when it adjusts itself down so far, it loses a lot of depth in the process. I didn't actually realize how much I was losing until I began checking. It was enlightening. I've noticed that once I'm under 15, I've lost quite a bit. By 10...well, let's just say that I don't find that to be acceptable.

So really, I was not entirely correct when I said that the auto feature is useless - it certainly does have its uses. I believe that it's causing me to miss targets though, and I've already proved this to myself in the field. In better soil I think that I'd be using it far more often.

 

[Mach1Pilot]

Hi Dave,

I think your entire problem is simply your highly mineralized soils. I've hunted the Culpeper, VA red hot mineralized soils looking for Civil War relics and found similar results - ie the (Auto) sensitivity to go as low as 6.. A bullet which will read 12-32 on top of the ground will read 19-32 just 4" deep... It will sound good, but the FE number gets real bouncy while the conductive number stays somewhat consistent. I've seen bullets at 7" sometimes just not even cause a response at all! (As found with another detector, see below)

But I had my best results running auto sensitivity, as suggested by Fletch88. Of course it cuts down the depth, but as you discovered a higher sensitivity means a lot of falling... This falsing caused me to miss targets.

About the only fix for this is a different detector.... As the Etrac is performing just about as good as it can in those conditions. My guess is that all VLF detectors will struggle in your soils, some will do better than others on some targets, but none will perform like they would on good ground. About the only machines that will work and achieve decent depth are ground balancing pulse induction machines, but they really aren't the best coin hunters because the discrimination level of even the best pulse induction detector is still a bit coarse to be hunting coins. (Not to mention they are expensive!!!$$$)

The answer for me in my hunts in the hot VA soils was a GPX 5000 .... No, I'm not suggesting you buy one but it makes the Etrac feel like a toy in comparison, and we all know the Etrac (which I love everywhere but there) is one of the best performers in the market. It's unfortunate but it's just not good in super hot soils.