Nugget/Coin Testing the JE/All Metal Motion modes.....

Hi NASA Tom,

Tom, I buried an oval shaped gold nugget about one-eighth by one-quarter inch dimensions, approx. weight of a grain or so. Buried at depths of two, two and one-half, and three inches respectively. In each instance the soil, a clay loam, was packed down firmly. The GB = 83 plus one detente step, the Fe3O4 meter read 0.1; the soil has some minor moisture...enough to make it easily compactible. A small kitchen magnet run through loose soil for a few seconds..comes up covered in iron "filings". That's the background information.
Two observations regarding the JE mode as follows....

(1) At both two, and two and one-half inches both modes at max sensitivity gave a "diggable" signal; at three inches the all-metal motion mode would not detect the nugget (a slight increase in GB did not help). The JE mode did detect the nugget clearly..a modest signal, but with room to spare insofar as I could lower the sens down to 80ish before I lost detection. At max sens, I observed the disc level could be run up to about 10 before the target was lost to detection. The nugget ID'd at 11 to 14 by the way. This test result was unexpected regarding the JE mode. Any machine I've owned, the all metal motion mode went deeper than a disc mode.

(2) With buried copper pennies (in my soil) at about 9 inches (freshly buried with brine sol'n added) the DE and PF modes will detect with a good signal at "0" disc and max sens, but as soon as disc is increased from "0" to "1", the target is abruptly gone...whereas...with the JE mode at max sens, the disc level can be run up to "13" before the target is "abruptly" lost to detection. But...at lower disc settings, say ""0" to "6", I observed that the sens could be lowered right down to "50ish", and still weakly but clearly detect the target. As the sens was lowered, the volume of the response was more modulated...no abrupt cut-off of detection. The "modulation" is much more noticeable in a "ground" test than in an "air" test.

So that's it. Two observations..the modulation as sensitivity is lowered while using low iron discrimination...compared to the other modes on coin targets, and the deeper detection of a small target (nugget) than the motion all-metal mode. You can see the potential implication for electronic prospecting, especially detecting mine tailings with iron trash present. Equal or better tiny nugget detection sensitivity, with the bonus of small iron discrimination. Unthinkable, until today that is.

Tom, can you explain what is designed/engineered into the JE mode that permits this mode to perform as described above? What did the designers do to this circuit? I can hardly believe what I saw today...........

Jim.

Jim good observation and Detail on test..There are lots of others that will agree JE mode is Deepest if soil conditions are worthy..So considering the other machines and your experiance with test results and real world detecting is it safe to say you like the F75 so far...Jim you bring another perspective to this forum..i am Glued to the screen to see Toms Technical explanation..Thanks..james

Hi James,

Yes it would be fair to say the F-75 is becoming a fast favourite. It takes some time to adjust to something different from the "traditional" units of the past, but now the old units no longer "feel right" anymore, so I've changed.

The question to Tom is not phrased well, and may not be a fair question. I'd like to know why does JE mode outperform the all-metal in depth on the small nugget. The modulation of the JE mode is more a curiousity, but I have to revisit that test to confirm facts. That means, make notes, not try to recall later what happened to the best of memory!

Jim.

Jim,

Your results, observations, methodology and written report are exacting, correct & superb. Soooo much to say..... not enough time! These are the pinnacle accolades of the F-75. ((( You are imminent of F-75 nirvana ))). The smallest/minute'-of-change in "certain" adjustments may equate to stupendous performance gains........ by no accident. Thus far.... you are the only other person that I know of, of whom has 'discovered' some of these "pinnacle" performance characteristics of the F-75 (and also able/capable to apply these major performance characteristics to real-life, real-world hunting scenarios).... AND AND of whom is willing to 'take the time' & effort to expend into the most minute' of attention-to-detail. With your newly discovered 'awareness' and set-up config's...... your performance in the real world will be above all others....... starting right now. Simply by virtue of 'awareness'.... the detector and your mind-set will open MANY doors. ---- If my words seem TOO strong for your newly discovered epiphany; in time, you will soon discover that my words are merely an understatement of your '''soon-to-be-discovered''' real-world detecting performance gains.
FIRST; The all-metal mode will trump ALL other modes of this detector (IRT depth/sensitivity) INCLUDING the "JE" mode...... UNLESS Disc is on '0'. So, to answer your 1st (most important) question: It is simply a function of Sensitivity/Gain as to why 'JE' w/Disc '0' will trump ALL OTHER MODES. Keep in mind...... in order to gain just a few percent greater depth (read = Sens)...... the required gain is not linear/logarithmic...... nor is it exponential; rather, it is asymptotic (a higher order deriv of exponential). In other words = It may take 64X more Sensitivity to ascertain 1" greater depth. The "JE" mode with Disc on '0' is just exactly this.
SECOND; With Disc on '0'..... acquiring the target,,,,,,....... then lowering the Sens ...... the performance change is rather/more a function similar to simply "lowering" the volume. Other secondary factors apply. Modulation control.
THIRD; The very small nugget you used is perfect for testing the "JE" function...as....... that's what it was designed for! NOTICE and KEEP IN MIND.... that NON-ferrous nugget ID'd as a ferrous 'iron' VDI reading....,,,,,,,...... mind you, it ID'd on the HIGH end of the iron scale (almost into the non-ferrous range). Hint - Hint!!! And notice...... as you increase Disc to say '10'.... the nugget will "Disc out".... even though it ID's HIGHER than your Disc setting. Hint - Hint again! In this particular case... it was not so much of a function of 'loss of depth due to increased Disc'; rather a function of Disc being a divorced function of VDI readings. ((( It lies within the finest of details ))). (((And isn't it bothersome to know that your kitchen magnet picked up plenty of Fe... Ouch)))!!!
FOURTH; Your "abruptly" observations are also exacting. BUT..... I MUST say this; ironically...... your Cu penny was buried at a depth so as to present the "maximum" differential between "JE" mode vs. DE/PF mode insofar as to make one think that the "JE" mode will detect coins/coin-sized targets at greater depths. Truth be known; the depth gain in "JE" mode on coin-sized targets is negligible..... if any..... under any/all circumstances. Had you buried the Cu pennies at 9-1/4" (ever so slightly deeper)..... you would witness the 'negligible' presentation.
I have only one person/friend (detectorist) of whom has witnessed the F-75's true performance. You are first-hand.
Jim, what you witnessed/observed today is real (and only the beginning)! Keep observing...... and reporting. Do NOT get discouraged when you find that..... many places (IRT to EMI) will NOT allow the use of "JE" mode..... or other modes with very low Disc settings....... or JE combined w/low no Disc settings due to electromagnetic interference. You will find that you will DELIBERATELY SEEK PLACES where you CAN indeed run wide open!
Now..... If only to focus on audio resolution.

Tom

Hi NASA Tom,

Thanks very much for that detailed response. Most kind, but I'm certain there is so much more to learn about this unit. A great deal of GB experimentation is needed on different target conductivities under my ground mineral conditions to see what if anything can be achieved or learned...especially wrt to modifying/eliminating iron falsing...if possible...in iron infested sites. I am familiar with an intriguing concept of lowering GB under such conditions, but have no direct experience, yet.

I don't doubt at all that the JE mode gets negligible, if any depth increase over the other modes on coin size targets. These tests indicate, at least in approaching the limits of coin size detection, that the JE mode will allow some use of the disc circuit, perhaps to reduce/eliminate small iron debris signals...a real advantage in providing "smoother" operation, while still matching the depth/sens capability of the the PF/DE modes...if, as you've pointed out, EMI conditions allow it's use.

I confirmed today, your advice above regarding coin depths. Buried another copper penny at 10 inches, added a glass of tap water (no brine sol'n), filled it in and compacted. The JE/PF/DE (max sens, zero disc) modes all just barely eeked out a two way signal that would definitely attract your notice and be investigated (dug). The difference was that again in DE/PF modes raising the disc from "0" to "1" would abruptly lose the signal...whereas...the JE mode would allow disc settings in the "6 to 7" range without noticeably impacting the quality of the audio signal...however most of the "modulation" was lost as I could not lower the sens below 80ish without losing the signal. So, that is that...but this is superb performance by my experience.

Rechecking the test nugget, the JE mode definitely gave a much crisper (and therefore more noticeable) signal than the motion all metal mode. In fact, at three inches and max sens, the motion all metal mode will give a "flutter", but not meet the test criteria = a repeatable two-way signal. However, the stat mode did perform comparatively well on the nugget.

The stat mode observations are not entirely clear yet to me. I found using the ground balance as established in the motion all metal mode, to be unsatisfactory insofar as the ground was one large signal in the stat mode....and thus I couldn't operate. So I lowered the ground balance from 83 down to 80 to get a workable reduction in signal volume as the coil approached the ground surface, then experimented with retuning at various heights above the ground to find a practical point where I could operate without involking spurious ground signals. Since it was difficult to find a "repeatable/useable retune height", I lowered the sens down to 80 to soften the harshness of the spurious noises, lowered the coil to within maybe one-half inch of the ground surface and retuned, then raised the coil about one and one-half inches above the ground surface...and "started hunting". This method at least allowed me to detect the nugget quite sharply with some small leeway in raising the coil prior to losing the signal (although of course, with no threshold sound). Further lowering the sens down to "70ish" provided a little more leeway in minimizing the spurious ground signals, but reduced the practical "operating height" of the coil wrt losing the target signal altogether.

One last comment Tom. Increasing the ground balance some 5 to 10 full units above correct GB in the stat mode, using the above retune procedure, did help increase the nugget signal response (whereas it did not noticeably help in motion all metal mode...that was a bit of a surprise but I think it's primarily because of the autotune, I did not and could not completely control the units retune response to ground signal at coil height variation), but because of the ground noise, I doubt it would be a practical/applicable real world technique in a jumbled height rock substrate prospecting environment. Also, by decreasing the ground balance lower than the 3 full units...resulted in "abrupt" target signal loss...so I had to find a workable compromise. I remain uncertain about drawing conclusions on these tests at the moment. Any input/guidance from you would be very much appreciated, as I am not familiar with the practical applications of the stat all metal mode for detecting tiny targets. I regret there is no autotune rate adjustment on this unit.

Jim.



Edited 1 time(s). Last edit at 06/06/2008 09:25PM by HumblePie.

Good reading here, just wondering what coil was use in the test? Would the small coil make a diffrence in the same test?

Jim I have experianced the same when using the stat mode..It seems to walk a bit
and can be intimadating to use for a rookie like me so i have kinda backed off till i get some time to test the unit in stat more..Your questions to tom are
right on for understanding the F75..I truley think Dave Johnson Designed the machine to Be one of the Best on the market and simplified for users that want to take the time to understand and test the unit like yourself,Tom and others..I am glad you decided on getting the F75 over the other units you were considering..Tom great explanation and Info about the Mode selections..you are so imformative..thanks james

Hi EZ and James,

Used the standard 7"X 11" DD coil; don't have the smaller coil just yet. Probably temporarily a good thing, since I want to focus on the standard coil for now. EZ I think we both can anticipate how the smaller coil would perform, but without direct experience on this unit with the smaller coil, I prefer not to speculate. We see too much of that on other forums and it leads to misinformation and much fruitless debate.

Rather, I defer to Tom's wider technical expertise, knowledge, and experience. This forum's primary appeal to me is Tom's objectivity in discussing facts, so I'd rather not advance unsupported opinions. Besides, I'm uncertain about drawing conclusions just yet on some points. It's fun to run a few simple tests and forward some observations for comment. Let's defer your question on the smaller coil for Tom's comment. Thankyou.

Jim.

The more real-world in-depth hunting scenarios we apply to the F-75; subsequently trying different set-up config's........ the easier it is to realize the F-75 is more than just one metal detector inside that small pistol-grip stalk. Switching to the Stat mode is just one example...... as this is a (modern/high-tech) good old fashioned TR non-motion unit. Jim, in your quest for hair-splitting differential exposure....... your test platform scenarios are textbook-perfect...... and your observed resultant parallels my testing datum (and expectations)..... with one difference/variable --- that being (somewhat predetermined/predictable) ground mineralization differences. With a plethora of different tests...... we can determine the hair-splitting differences and see if they are applicable to 'usable' status. Many times, the differences are so minute' which makes it difficult to justify usage; yet some pleasant surprises come to light. I have yet to find a site that can justify Stat mode usage....... where Stat mode becomes the premier 'mode-of-choice'. I presume relic sites with high concentration levels of magnetite. . . . although, (in general) Motion All-Metal would handle bad ground slightly better.... in many cases.
... All said-and-done, , , If the ID side of the house (especially Disc '0' and/or JE mode) out performs the All-Metal mode....... seems to me,,to be a moot point for usable application. Sure is interesting to experiment though. And I'm glad to see you witness the vast differences between air-testing vs. real dirt.
---There are attributes of having a full Disc range ID capable unit that can be utilized for prospecting; however, the Gold Bug-II (specifically/ONLY designed for prospecting) still shines. BUT...even though the GB-II is more properly resonant to Au by virtue of it's 71 KHZ operating freq...... I often wonder how the newer technology F-75 handles bad dirt vs. the Gold Bug-II. Both are single freq units.
......Your robbing-Peter-to-pay-Paul experience of detuning this and retuning that,,, so as to compensate for your "live" dirt in Stat mode is apropos; on par with TR characteristics. ..... And having to detect with the coil inches above the ground seems self-defeating..... yet sometimes required. And yep,,,, Grnd Bal becomes critical to both depth and ID performance in more severe dirt. In general, raising Grnd Bal can enhance detection of tiny targets; HOWEVER, the signal will become more 'awash'. Human Intelligibility is paramount!
### Still seeking to find 1/16" greater depth on a dime!!!

... IRT the small coil; strangely....I have yet to find adjacent target seperation enhancements with the smaller coil; however, it does fit in to tighter places better.

(((( Feel like I'm hardly explaining things clearly/properly )))).

Tom

Hi NASA Tom,

I appreciate your comments, and did expect/invite "conversation", with no expectation of earth-shattering declarations. Sometimes it's as straightforward as, "yes that will work, or no that's not a viable real world technique. You've provided that perspective, and I'm quite pleased and satisfied with your remarks.

A few thoughts: (1) to my view, the motion all-metal mode is more practically useable by comparison with the stat mode for detecting tiny targets. No doubt, fine adjustment of the sens and GB settings to some extent will perhaps gain a slight "edge" on those small nuggets. (2) prior to purchasing the unit, I was not fully aware of the JE mode benefits, either (a) for using small iron disc capability on "deep" coin size targets while still matching the depth capability of the PF/DE modes, or (b) the JE mode's exceptional small nugget detection sensitivity at good depth. This mode is a windfall, and opens a door for prospecting use that I never would have thought practical. Yes, many electronic prospectors use some disc in trashy tailings, but with considerable sens loss as well as small gold; the JE mode may challenge long term and closely held ideas regarding disc modes for prospecting at least grain size targets...for those who are aware of it.


As you noted above, having the attributes of a full disc range ID capable unit that can be utilized for prospecting offers significant advantage. (1) I don't want a unit that will detect the very tiniest pieces of metal on a par with the GB2; this does not normally represent the best use of my time. Locating such tiny signals in mine tailings is an annoying distraction, as the focus is on somewhat larger targets than small sub-grain pieces. In natural prospecting settings, that is an acceptable sensitivity loss for me. (2) discrimination circuits, particularly the JE mode, plus visual ID in the all-metal mode as well, provides options as to how the user searches trashy mining areas, as compared to some prospecting units lacking visual meters. Information regarding ground phase, and iron oxide amounts...in addition to target ID visually displayed can only enhance the prospecting experience. (3) the F-75's lower operating frequency should enhance this unit's relative performance in higher mineralized substrates, especially on larger size nuggets/ores, in comparison to dedicated units with much higher operating frequencies. (4) if tiny nugget detection on a par with the GB2's stock coil ability is an issue, the F-75 does have a smaller coil option that will be more sensitive to smaller sub-grain pieces. Whether the smaller coil will provide any depth increment on a grain size piece is an open question to any forum readers who do have this coil and wish to do the test; I suspect it will provide better sensitivity, but am uncertain if it will translate into more ground penetration. (5) obvious coin/relic hunting capability can be handy in any area.

That's it for now, and thankyou Tom,

Jim.



Edited 1 time(s). Last edit at 06/07/2008 12:45AM by HumblePie.

Jim,

You sound EXACTLY like Dave Johnson. Your thought process, intelligence, conceptual notions etc.....
Yes, I see merit in a prospecting detector that can NOT see the very tiny gold flakes..... allowing you to concentrate on the slightly larger nuggets; however, as you would expect, by virtue of NOT being able to detect the VERY tiny nuggets/flakes.... you also forfeit the slightly larger nuggets at greater depths. A expected trade-off.

Tom

Great post jim..and very good points...Tom I understand Dave Johnsons thinking when he Built in the JE modes performance from this tread lots better now..Thanks..But for me any grain of Gold will warrant a huge party...Tom / Jim Is it true that tiny flakes sometimes lead to bigger nuggets in raw forms..james.

James: Yes, but it's painstaking work, and rarely does anyone hit a bonanaz anymore in accessible areas. The oldtimers were adept at following float/placer trains back to source, but not entirely thorough at cleaning-up deposits. Best to view prospecting as an enjoyable hobby with the great outdoors health benefits.

NASA Tom: Those remarks are most kind. Tom it's interesting, the differences encountered between operating frequencies, and not always so clear in drawing conclusions when other design/operating factors also impact results. Your observation above is absolutely correct in my experience. With that in mind, here's an example that I cannot verify, not being on site at the time, and frankly am reluctant to repeat, but only for the sake of "conversation."

A well known, high profile individual in the metal detecting community, a renowned prospecter and personal acquaintance performed an unscientific test with both the GB2 and F-75 on various size nuggets, in highly mineralized soil. That's the important factor here...highly mineralized soil, because I doubt the test result would be the same in less mineralized soil. The GB2 outperformed the F-75 on sub-grain nuggets both in terms of signal quality, and depth (although all depths were quite shallow). This should be expected, given the GB2's much higher and thus more sensitive operating frequency.

However, the "crossover point" occurred at approx. the one grain nugget size. At this point, the roles reversed, and as nugget size and depth increased, the F-75's performance similarly increased over the GB2. It is to be expected the F-75 will perform more effectively for larger pieces at greater depths, so really no surprise here, given the, in many ways ideal, 13kHz operating frequency. But keep in mind the overall perspective.. we are referring to a very slight "edge" only, and may very well not result in any practical/significant net difference in finds at any given location.

The foregoing test description is heresay only and I am not in a position to confirm it at all...and therefore must be viewed as highly suspect. Relating a story, and nothing more. Within the prospecting community it is generally recognized that the GB2 ground penetration in high mineral substrates does suffer a bit, due presumeably to the relatively higher operating frequency. Still though, all factors considered, the GB2 is a top flight unit, perhaps rivalled overall only by the GMT in terms of natural terrain searching.

In selecting an appropriate unit, we must account for anticipated potential conditions including ground mineralization, iron trash/debris present, type and size of target objective, an expectation of positive hot rocks, and so forth. If the objective will primarily be sought in a mine tailings environment where all these factors come into play, a unit with the F-75 attributes seem ideal. It's about selecting the appropriate tool to get the job done properly. Plus overall, the F-75 offers considerably more for other endeavours, I doubt anyone would contest the validity of that observation.

Yes, Dave Johnson. I was in touch with him a short while ago regarding iron mineralization detection wrt evaluating iron mineral effects on ore evaluation. In short here's the sequence of events....for the sake of conversation and interest.

Knowing that iron can arrive on site in many (ionic bond configurations) forms, from the ferrites to the weathered limonites (nature's rust, a hydrated ferric oxide), I wished to assign a "value" within the ground balance scale as a reference point whereby any iron mineralized rock would give a "negative response" both, in the absence of any contained native metal, and without venturing into the iron metal or salt ranges of the GB scale. Various tests with samples resulted in an unscientific setting of "40" on the GB scale as the reference point. I fully realized this setting would have the undesireable effect of placing the full weight of iron mineral bias against any measurable amount of (perhaps quite disseminated) "metal" that might/possibly be present in some samples.

Subsequently, I emailed Dave Johnson requesting his evaluation on the appropriate GB setting, and indeed, was advised to stick with a setting of "45" for all weathered iron mineralized rocks, and in an effort to reduce the iron mineral bias, to try "65" for non-weathered rocks (a visual estimation for the layman). Thus, you can imagine I was somewhat pleased with my test results, although not entirely satisfied all potentials have been suitably addressed..obviously some minor disseminated metals will not have the strength to overcome the iron mineral bias, and currently my best estimate is that a visual evaluation of the rock...especially in the case, for example, of silicates and carbonates showing iron "staining" is still unfortunately, probably the best alternate evaluation method available to me. For example, if visual indications on stained quartz would indicate the likelihood of a "negative" reading, and the result is otherwise, then more physical examination is warranted, the rock hammer, acid bath, grinding, and so forth.

Soooo interesting, and intriguing...detectors do so much more than go "beep". That's it for now, thankyou Tom for lending your ear, and for your astute and knowledgeable comments, you have been highly instrumental in my thinking and adaptation since my first post here. Thankyou.

Jim.

PS: I did edit the above original text to keep it simple (Saturday 10:50 PM)



Edited 3 time(s). Last edit at 06/08/2008 02:48AM by HumblePie.

If only to achieve geophysics quiescent/null status amongst the multitude of dirty dirt variables so as to alleviate inherent EM attenuation & negative effects. Once again; here we are,,,,,,, utilizing this electromagnetic principle-of-operation device...... applying it to electromagnetic bad dirt,,,,,,, all with expectations of locating non-Fe targets. Counterproductive indeed! Paradigm shift overdue! TOO much focus placed on: "But it's so cost productive...... and all other platforms are time/technology/cost prohibitive." Yet we push current technology to the N'th degree. I'm one of them.
Pulse Induction has always fascinated me by virtue of the fact that it is still a EM envelope,,,,, and should be severely affected by bad dirt, yet a paradox exists. It still provides formidable depth capabilities, even in heavier ferrite environments. Granted; (currently) PI's require desirable targets to be greater than that of the smallest flakes that; say a GB-2 will acquire. Time-curve decay rate measuring........in EM hot dirt....... still amazes me. This should be akin to reading the date on a dime submerged in molasses.

Tom

Can't wait for the day they come out with a PI unit that discrims. Great and informitive discussion upstream. Thanks Humblepie for posting it.

Hi Tom....thankyou very much for a most interesting discussion. I think that about covers my questions for now. I've been observing that the disc settings for JE mode vs the PF/DE modes is quite different for identical "in the ground" target conductivities, at least in reference to iron and other low conductive targets...have not checked higher conductivities yet, but will do so. More tests needed, before I presume upon any more of your valuable time. Thankyou.

Jim.

Hi Kas....it has not been widely known that Eric Foster's GS5 PI unit has some disc ability. For example, it is possible to eliminate all forms of iron, large or small, while still being able to get target responses from targets that meet the minimum criteria for "high conductive" low responses ie coins, screwcaps etc. This is achieved by arbitrarily setting the ground balance control to the appropriate setting, in this example, the setting is at the 10:00 position. Other factors, ie coil design, mineralization and so on do come into play, thus impacting user discretion regarding desired discrimination vs sensitivity (depth) loss. There is considerably more involved, but we'll leave that for another time.

Similar results are now becoming widely known from the new TDI Pulsescan, plus the TDI also incorporates a "tone suppression switch" which can be quite effective in eliminating either high or low tones, as well as suppression of ground noise (which signals as a low conductive "high tone") where the GB is again arbitrarily set to a desired disc level, at the expense of proper ground balancing. We could discuss it's capabilities at length, but I'd rather leave the subject at this point, for now. Thankyou.

Jim.

Yes, Indeed..... the JE mode employs different Disc parameters/operating characteristics vs. DE/PF modes. I believe ..... somewhere long ago...... on this forum, I covered this topic. What an attribute........ to have this 'JE' mode,,,,, subsequently converting the unit over to a very different platform; however, dangerous for the novice/beginners.

.....On a different note; I owned a Gold Scan 5...... and could not acquire GB on Florida salt beaches. Bill Crabtree took a flight down here to validate this problem, including his own GS-5. Without GB..... the units limited ability to Disc was severely hindered.

Jim, Thanks for your 'key' contributions here!

Tom