6 inch MF coil soujorn.

[BarnacleBill]

Since there seems to have been few posts of finds with the 6 inch concentric MF 7.5 KHz, I decided to take one for a spin through an "iron rich" area with the X70. I have to admit it is tough for me to take the little 6 inch DD HF 18.75KHz off, since I like it so well for a variety of reasons.

The area chosen, dates back to 1900 or so for any significant habitation by we of European heritage. Since I have detected the area for years using a variety of machines and coils, I expected to find a few coins, lots of little relically pieces of brass, lead, copper etc,. and tons of iron. Much of the area is located in a pine thicket, and any unfortunate clad coins that don't make it through the 4 inch thick highly acidic duff quickly, lose their silver within a few years. So the phrase "one thin dime" really applies, because there are a couple of very thin copper dimes from the 60's & 70's in the photo.

I have access to hundreds of acres on this site, but concentrate on those "choice" areas that I have determined from maps and old photographs, and admittedly I have not strayed much out of a couple acre zone since I know there are thousands of targets still buried. The particular section I chose to work has a thick iron density, so that usually there are 2 to 3 iron targets under the 6 inch coil at any one time. Despite how fast a machine is in recovery, larger coils need not apply, and if the detector needs a fast sweep speed, you are SOL! Now if you want a headache just use "All Metal All the Time", 'cause you'll be laying head to pillow hearing grunt, grunt, grunt......kinda like sleeping on a hog farm.

During the several hours (~3.5 hours) I experimented a little with settings and technique. I ran a slight threshold 3-4 for about half the time, but even that got annoying as there was constant nulling. I used Pattern 1 for the most part, and set Pattern 2 up as a reverse discrimination slot that had the opposite accept/reject slots as Pattern 1. There is some danger in doing that on the X70 if you forget to select twice and end up in Pattern 3(guilty). The X50 is a much better choice for using that technique, much more foolproof. I pinpointed once in a while and went to All Metal a couple of times when checking on iffy's. All in all only about a third of the targets gave a clean clear signal, the rest were mixed in with nearby iron bogies.

If are hunting an iron rich area like I describe with Tracking on, then you need to either turn Tracking off when you set it down to dig, or find a target free area and turn Tracking off, then on, to have it fast Track for the first couple seconds. If you don't, the Tracking will wander when you have it setting next to you, then when you are finisihed with that hole, for about 30 seconds the GB will be out of adjustment as you start to hunt again. In a sparse target area with little iron it's no big deal, but for optimum discrimination in iron your GB had better be right on the money.

What's probably most notable in the photograph of finds, is what's not in it, and that is any steel or iron. I passed over hundreds of targets, and dug many iffy signals without getting any rust stains on my gloves. There are two found items missing, one was a tube of something(toothpaste, shampoo etc) that I cut in half with my Lesche, and was filled with a white substance that was leaking all over my pouch, so in the trash it went. The other is a plated brass clasp for use on canvas/nylon straps, but it is encased in a sand/clay mix that I am soaking in water to loosen up. The only notable find is the green 1918 wheatie, but the target mix size/conductivity and no iron, should give a good idea of what the 6 inch MF concentric can do. If I had an X30 it would definitely be on my X-mas list because it would open up so many areas that a larger coil just can't compete in.

Photo from from ~1900 of the area I was hunting.
[attachment 72385 c1.jpg]

Finds.

[attachment 72386 6b.jpg]

HH
BarnacleBill

 

[Jackpine Savage]

Definitely not all metal but close and worked for me on the X-70. Slight threshold and use pattrern 1 modified to eliminate only the worst iron offender for the site. By watching the ID screen note which iron segment is the busiest. If -4 is the offender, that zone got notched out. Don't forget the sensitivity setting either. A too high setting in iron just adds tons more iron signals and clouds the picture. Find a sensitivity balance between depth and iron hits/nulls. The small MF coil sounds like a god send for allowing higher sens settings and oh yeah, 2 tones like Monte always says.

Tom

 

[John LA]

Very interesting Bill but I didn't get the felling that I should purchase the 6" concentric. Is this the same location where you use the 6" DD?

 

[wpaxt]

Like you, I have a real tough time taking off the 6" HF DD coil. If you had your choice would you have chosen the HF DD over the MF concentric in this situation, or do you feel satisfied that the MF concentric did an adequate job?

Also, I agree with you as to the 6" MF concentric being essential if you have a 30. I personally really like hunting with the 30 when I just want to swing & listen (i.e. no messing with settings) and having that small coil option is killer.

Thanks for another one of your informative posts.

Bill

 

[BarnacleBill]

"1. Very interesting Bill but I didn't get the felling that I should purchase the 6" concentric. Is this the same location where you use the 6" DD? John LA"

"2. Like you, I have a real tough time taking off the 6" HF DD coil. If you had your choice would you have chosen the HF DD over the MF concentric in this situation, or do you feel satisfied that the MF concentric did an adequate job? WPAXT"

Yes this is the same place that I tested the 6 inch DD. I do much of my comparing at this location because of the wide variety of ground minerals, history, target density, variety of target types, and iron. I don't want to bore anybody because I could probably write 2000 words just describing what it has to offer. My great-great grandchildren may just begin to scratch the surface, depending on what technology becomes available. As an example, there is an area I know was a cook shack, there's several hundred square feet of buried, rotting, rusting cans. I stumbled across it doing some scouting, but I don't detect there because it's such a hassle, and I don't have to, I'm not that desperate.

The CC versus DD is an interesting conundrum and I'll try to clarify between what I know & don't know. First some of what I believe is the accepted conventional wisdom.

CC
1. Low freqs achieve greater depth in higher minerals.
2. Low freqs are more responsive(deeper) on high conductors.
3. Low freqs discriminate against iron better.
4. Some claim to hear(distinguish against) iron better with a lower freq.
5. A concentric coil induces a bowl or cone shaped field into the soil.

DD
6. High freqs are better(deeper) on low conductors.
7. High freqs work better at locating very small targets.
8. DD's are better with a high mineral content.
9. DD's induce a blade shaped field into the soil.

What I know for certain concerning the two small coils.

1. Assuming normal coil swing left-right = E<>W, then yes the DD separates better E<>W, but I can't say for certain that the N<>S tip(edges) of the coil don't cause some masking. Anecdotally if there is some masking going on, I'm not noticing it, but I haven't proved it for certain.

2. The DD is without any doubt in my mind is more sensitive to very small objects and lower conductors. The CC makes surface foil strings sound pretty ratty, dull-ish, broken.

What I don't know.

Here's where things get real muddy, especially when I consider where I was detecting. The soil where I was detecting is mostly white sand based with very little mineral content, so that the DD has no advantage as in point #8 listed above. But by the same token the lower freq of the CC should not gain an advantage as in point #1 listed above. Is that part of the equation a wash? I was also over thick duff(3>4 inches) for some time, does either of these coil's field shape, or their frequency couple better into the ground from what amounts to a 4 inch air space? I honestly don't know.

If say a penny is 8 inches deep, will the CC lock on better because of a lower freq, whereas the DD would miss it because of freq? Or is the DD's blade shaped field more concentrated, which washes out the lower freq advantage? If it's a nickel what happens? Up to now these are the easy questions, now take the above points and mix them in with thick iron. Which coil is suffering more from iron pull-off/edge effect? Are two shallow iron items near the N<>S edge of the DD masking a deeper target toward the middle of the coil? Would the CC see down through better because of a cone shaped field? What if you step left 45 degrees and the DD now has a cleaner shot? Does the CC remain masked because of equal field strength around it's edges over this same target? Now what happens in soil filled with nasty minerals? So many questions with so few definitive answers!

So in the end I prefer the DD, but there is some bias on my part because finding small gold items is my preference over coinshooting. If I were a Silver Hound, then I would have to think about that more, and probably prove to myself that the DD was still my best bet. But that proof would involve several hundred hours of field work if you want to do it right, gridding, cataloging, and data entry.

I think either coil will do about 80% of what the other will do overall. However the differential from the larger coils comparatively is much greater. If I had an X30, there's not even a question that against the high end machines sporting big coils, you'd mop the floor with'em in high trash areas. Especially those high end machines that don't have the notching ability of the X30, just show them the magic trick. Wave trash over coil, hit Accept/Reject, and presto no problemo!

OK, I've drooled on the keyboard enough.

HH
BarnacleBill

 

[Digger]

Good analysis Bill, I agree that there is little difference in the hunting abilities of either 6-inch coil. At least as far as depth and sensitivity is concerned. As I have posted previously, my choice of using the 6-inch DD coil (opposed to the concentric) is contrary to all the data I have collected while using the larger coils. Before the introduction of the smaller coils, I preferred the 3 kHz concentric over all the rest. I liked the concentric because in my soil, it just plain goes deeper. And I like the 3 kHz because I do get a better rejection of low conductive targets and I can hear a more distinct low tone on ferrous targets. However, with the two 6-inch coils, the DD at 18.75 kHz has found me more keepers than the Concentric at 7.5 kHz. Maybe it is the old "I use what works for me" syndrome in that I use what I find the most with. When I have "good luck" with a coil on a specific outing, that is the coil I start with the next time out. The more I use it, the more I find. And the more I find with it, the more likely I am to keep using it. That is the problem with trying to rationalize "real world" experiences. I know that I found more coins with the DD coil. But in all honesty, I would probably have found those same coins if I had been using the concentric. But, since I wasn't, I convinced myself that the DD coil is better suited for my style of hunting. Like they say, you dance with the one who brung ya!

The "conventional wisdom" as you mentioned, tells us that the lower frequencies are better suited for higher conductive targets such as silver and copper. Conversely, the higher frequency coils are better suited for lower conductive targets (such as gold) and are suppose to be more sensitive to smaller targets. And if we were comparing the 9-inch concentrics, I would agree with those theories. But I've not found much about these 6-inch coils that follows the so called "conventional wisdom". Case in point.....I believe this little 6-inch ignores the "cone shaped" detection pattern associated with concentric coils as well. To support my hypothesis, try this simple test. Set your detector up so that the 6-inch concentric coil is suspended in an open environment. (nothing metal to interfere with the test procedures). Now take a coin and pass it back and forth under the coil, making sure to over-sweep the width of the coil bottom by several inches. Notice how, when you are holding the coin close to the coil, that there is signal produced when the coin is outside the parameter of the coil itself. This is what I was referencing when I mentioned the coils were extremely "hot". Now slowly expand the distance between the coin and the coil while continuing to pass the coin back and forth under the coil. Make a mental note of the detection pattern as you slowly continue to increase the distance between the coin and the coil, until the audible tone is gone. From my observations, the pattern is not shaped like a cone in that as you near the maximum depth of detection, the detection pattern more closely resembles half a sphere. I think I once referred to that pattern as resembling half a melon! In other words, if you took a melon that was 6-inches in diameter, cut it in half, placed the cut side against the bottom of the coil, then lowered it 3 or 4 inches, you would be looking at the shape of the detection pattern of the 6-inch concentric. When performing the same experiment with the 6-inch DD coil, I've found that the pattern is more concentrated toward a vertical line running from tip to back, along the center of the coil. Like the concentric, it is extremely hot on shallow targets. And on shallow targets you will detect shallow targets "outside" the front and back edges of the coil. But as you move the target away from the surface of the coil, the pattern becomes more centralized along the center (tip to back). As such, I have found that the deeper the target, the more isolated the target becomes. That is not something I have found to hold true with the "melon shaped pattern" of the concentric. In fact on most buried targets, the DD coil is so sensitive at that center "line" of detection that I never use the pinpoint mode. After I have heard the initial audible report of a target, I simply wiggle the coil back and forth over it, as I slowly drag the coil toward me. At the very instant when the audible tone disappears, the target is always buried directly below the tip of the coil. Exactly below the tip!

So what does this prove? Nothing, I suppose. But I find it interesting to learn what each of us expect from (and appreciate about) our equipment. Like you, I also prefer the DD coil. Even if it is operating at 18.75 kHz. (I'm willing to trade off a few additional bits of can slaw for having the separation characteristics provided by the DD design) And, like you, I think the difference between the performance of these two coils is negligible. But I do prefer the separation characteristics of the DD coil. For many others, the greatest advantage of the DD coil might be for those hunting in more mineralized soil conditions. I am fortunate that I don't have to. Since the X-Terra 30 has a preset GB, and not capable of adjusting the GB as are the X-50 and X-70, having a 6-inch coil that works with it is a good thing. The X-50 and X-70 users with mineralized soil conditions have the the option of using either. Considering my preference of the 3 kHz coils in the 9-inch concentric size, and my appreciation for the 6-inch DD design, can you imagine how much fun I would have if they came out with the 6-inch DD at 3 kHz? HH Randy

 

[John LA]

n/t

 

[a1mine]

I have a question regarding conductivity as it has been raised in this discussion.

It is mentioned that Silver and copper are highly conductive and Gold is a lower conductor. Does any one have a chart of various metals and there position on a "coductivness" chart?
They use gold which is a poorer conductor than copper on electrical contacts. Possibly as it may not tarnish as much.
I do not really understand the issue as it relates to coil size and frequency. Can some one give a simple explanation.
Another question is, would a large piece of copper be a better conductor than a small piece of gold.

Sorry for sounding so naive but I do find it puzzling.

Ken

 

[BarnacleBill]

Here's a chart(not my work) related to US coinage & other common objects.

[attachment 72516 DiscriminationChart.jpg]

And yes a large piece of copper is much more conductive than a small gold ring. What makes gold jewelry challenging is that it is alloyed most of the time with other metals of various conductivity , as well as coming in so many shapes and sizes. I think JackPine the Savage man found a big ring that ID'd up around 28, which is way up the scale compared to where most gold jewelry comes in.

In general higher frequencies are used to hunt small low conductivity items like small gold nuggets, and therefore work better at finding gold jewelery. Small coils appear to be more sensitive to smaller objects and larger coils to deeper/larger objects. But this is all very general and does not take into account various coil designs. Part of the thought behind the X-Terras was to optimize the coil frequency to the task at hand. Prospectors and gold jewelry hobbyists will use the HF 18.75KHz coils for the most part, whereas the Silver Hounds will go for the 3KHz and the generalists use the MF 7.5KHz coils. Relic hunters have an interesting scenario, they are looking for a broad range of conductivities, therefore may use the 7.5KHz if they are going to pass over an area once; but may want to go back with a 3KHz or 18.75KHz coil if they can hunt the same area several times.

HH
BarnacleBill

 

[Jackpine Savage]

That ring was a solid zinc reading but was found with a different brand. Probably the highest reading gold band I have ever found although a couple others were close.

<center> Don't ya just love the color of 20K gold!<p>Swedish Hallmark made in Stockholm in 1897!

[attachment 72551 20kebhlmk.JPG] </center>

 

[BarnacleBill]

n/t

 

[Mick in Dubbo]

Thanks for your post Bill. Very informative. Yep, them 30's do a pretty good job. I prefer it to my Explorer. I love their quick responsiveness and ease of use Now if they had a back light for night beach hunting; how sweet would that be.
Mick Evans.

 

[Jackpine Savage]

IACS (International Annealed Copper Standard) conductivity chart. Its interesting to note that adding even small amounts of other metals will lower a materials rating. Copper and silver are often alloyed with gold to make rings with the result being that the alloy will rate lower than either metal by itself. As Bill stated size and shape also make a difference. Mens bands with a large cross sectional dimension like the one I posted below read higher than thin bands and a 20K ring (more pure gold) will read higher than a 14K ring of the same size because 14K gold contains a greater percentage of other metals. A pure copper ring would of course read higher still.

Tom
IACS chart

 

[Jackpine Savage]

It was a late season find at a very small beach used mostly by locals. Very few targets of any kind are ever recovered at this site even though I believe I'm the only one wading it. The lake bottom there is sand over clay and this ring was apparently a fresh drop cuz it was in the first scoop, nowhere near deep enough to get to the clay layer where it would have stopped.

HH Tom

 

[Jackpine Savage]

and I hope I can explain this so that it is understandable.

If for instance you take the chart that Barnacle Bill posted as one case, the degree spread, or you could call it phase seperation, displayed on the chart only represents one frequency of operation. A higher frequency of operation would tend to "bunch up" the reading of high conductive coin and in turn spread out the phase relationship of lower conductive targets. A good example is the Whites DFX where when using the higher frequency by itself the engineers normalize the readings displayed on the meter via software so that the operator can better tell the difference between a silver dime and quarter.

Hope this helps a bit

Tom

 

[wpaxt]

As much as I would love to, as you say put in"several hundred hours of field work if you want to do it right, gridding, cataloging, and data entry" (uh, yeah, sure I would), I think I'll still stay with the DD. I am constantly surprised how good it is on coins, at least in my soil it is very much the equal of the concentric, plus I love the superior separation. Now I just need to free up some time & get out there.

Take care, Bill.

Bill

 

[Beale]

Ok so the DD is a great coil. I have the 18.75 eliptical (came with the detector). Here is my question.

I plan o trying this coil very soon. Will my ID # or tones change on my finds? I really want to try one of the small coils but I gotta do baby steps. One at a time. Any help is welcome, Beale.

 

[Reconmarine63]

Excellent post I agree it sometime tough call to hunt with my 10.5 DD 7.5 or 9 inch 3 kHz Coil. Since I hunt Civil War Relics you can cover more in ground coverage then CC coil . It tough call but, If I'm hunting new site or looking for hot spots I use the 10.5 DD. Once i get in good spot or old hunting area I switch 3 KHZ coil since I can hunt slow and go deep. One big advantage the X-70 has over all others!!

 

[BarnacleBill]

The small DD should act the same as the elliptical ID wise. So if in your clean soil, no iron/no trash, but depending on mineral content, it should ID the same. One of the difficult parts of making coils for any manufacturer is matching them to existing coils in the way they respond overall.

But that being said, I don't know how much experience you have poking around in trash with a small coil. In trash ID's will shift much of the time, because the signals are mixed, a composite, or hybrid if you will. Most people buy a visual/tone ID machine, so that in hunting they want the machine to prove to them that the target they are investigating, is a good target and worthy of digging. That is fine when covering an area relatively trash free with isolated targets. However, when say digging in iron, a negative sort of logic will serve you well, and that approach is to make the target prove to you it's iron. If the target cannot prove that it's iron, no matter what the ID readout, dig it up. If you are just starting out, you will dig up some iron, everyone does. But over time as your skills improve, and you become more experienced with the tools you use, the good/bad ratio will improve. Just before digging the target, play a little game with yourself, estimate what the target is and ask yourself what ID/audio/visual response makes you think that. Then after recovery, assess and ask yourself what you could have done differently to improve your approach. i.e. Varying sweep speed, coil height, angle of attack etc.

If you are already an old iron picker, then disregard the above and prepare to grin on your first outing with the small DD.

HH
BarnacleBill