Jump to content


  • Posts

  • Joined

  • Last visited

 Content Type 


Detector Prospector Magazine

Detector Database



Everything posted by PimentoUK

  1. And it also shows the plateau of signal strength at close distances that mono coils show. If that were reproduced for a DD, the blue trace, for example, would keep going up, to 100000 ( very approx ). Simply put, when a target is in the middle of a 10" mono coil, it's still 5" away from the nearest coil winding. Whereas a target in the middle of a DD is just 1/2" or so from both TX and RX.
  2. Carl: The graph I was thinking of was prepared by Mr.Green, in a thread related to finding the optimum coil size for a given target/depth. We discussed Eric's semi-circular graphs, and then Green used the 'Hyperphysics' website to analyse a mono coil. When all the maths misunderstandings were sorted out, the result was a neat Excel plot. This is the thread, post #39: https://www.geotech1.com/forums/showthread.php?24020-detection-depth&p=237587#post237587 "I charted distance vs amplitude with Hyperphysics for a 200, 300, 400 and 500mm coil to see if that would help determine best coil size. Her's an attempt at charting the coils. Example: a 200mm coil can detect a target at 400mm, what diameter coil would detect the target the greatest distance? The 500mm coil has the same signal amplitude at almost 600mm distance. A target just detectable at 100mm with the 200mm coil wouldn't be detected with the 400 or 500mm diameter coils at any distance." [when I get on a newer computer, I'll edit this post with the graph, and sort out the hyperlinks. This ever-changing forum keeps outsmarting my browser]
  3. That graph shows this not-too-intuitive phenomenon quite well. It also applies to PI machines with mono coils. And it's possible to calculate mathematically the behaviour of mono coils fairly easily, so it can be shown in a theoretical way, as well as physical measurements on a real detector. There are some discussions over on Geotech1 forum where charts like the above were posted. PI's do see the ground differently. From some discussions on Geotech1, I recall Eric Foster stating that PI's pick up the same level of ground signal regardless of coil size. And a mono coil has quite different behaviour to DD's ( and CC's ) when the target gets close , ( below 1/2 of the coil diameter away ). Essentially, the signal strength plateau's at close distances, whereas for a DD, it continually increases ( in practice, until the target touches the coil housing).
  4. Quote:"So ... you say a small coil will have trouble to detect bigger items?" Yes, a small coil will give a smaller signal than a 'standard' coil, on a large target. And a large coil will give a larger signal than the standard coil on that target. Roughly: Going from a 10" coil to a 5" coil will result in 1/6th the target signal. But ground signal strength will be down by a half, so there's the possibility of increasing gain and/or sensitivity, to leave you with a 1/3rd drop in signal. This would equate to 80% of the standard coil depth. Quote:"Thanks for trying to explain Induction Balance" I didn't explain it. I did point out there are engineering design constraints for small ( and large and standard ) coils .... the designer can't simply wind three times the number of turns on a small coils' loops to make up for the loss of signal, because the result would be incompatible with the detector.
  5. Quote:"could you please explain this? : "small coil has .. less sensitivity on big targets"" On a VLF machine, the precise inductance and resistance of both coils ( transmit and receive ) is important. Hence all coils, small or large, for a given machine need to have exactly the same inductance & resistance. This then determines how many turns of wire go on the TX & RX coils. This combination of different size loops, different number of turns, affects the strength of the transmitted magnetic field, and the sensitivity of the receive coil. A smaller coil simply gets a smaller signal from a target, so the target needs to be closer to be detectable. Vice-versa for the larger coil. On the plus side, a smaller coil also picks up a smaller ground signal, which helps the detector pick out the 'target signal' from the 'ground signal'. Other relevant factors include: Does the detector know it has a small / large coil fitted ? If it does, then small changes to the way it operates, such as gain/sensitivity changes, ground filtering characteristic changes, can be made, to mitigate the effects of the new coil. Machines that will almost certainly do this include XP Deus/Deus2, ML Equinox, XTerra's. But the majority don't, and it's down to the operator adjusting sensitivity up/down etc to make the best of a different coil size.
  6. Here in the U.K , some archaeologists are very critical of metal detecting. One reference article used when assessing the prevalence of detectorists is this Hardy article: https://www.tandfonline.com/doi/full/10.1080/23311886.2017.1298397 I haven't given it more than a quick scan, it may have worthwhile info in it.
  7. Ploughed land is indeed difficult, for several reasons. And it's difficult to reproduce, so it's not surprising that no-one talks about depth in such ground. Depth tests are mostly relevant to flat, undisturbed ground; public parks; pasture farmland; woodland; grazing land. But these are where targets can be, and often are, deep. And the deep targets are potentially the desireable ones.
  8. I'm not enthusiastic about 'test boxes' either. They need to be pretty large, especially for most single-frequency machines, that use filtering to help seperate ground-signal from target-signal. Multi-freq machines are not so dependant on this ( I think ), relying on measuring the ground at two ( or more ) different frequencies to largely reduce ground signal. Also, real ground is compact, which is hard to replicate in a box. When I buried my test-garden items, I used a lump of wood ( 2" x 2" / 50mm x 50mm) to pack down the soil in 2 inch layers as I refilled the hole, ensuring there was minimal inconsistency in the site. I didn't want my machine false-detecting the hole, nor the opposite effect, suffering reduced performance due to ground-signal fluctuations.
  9. Yes, the ground is the BIG variable. Some testers go to some trouble 'sanitising' their test ground ( removing stones, levelling the surface ..) which has the effect of making it easier to detect targets. Plus ...no-one has any equipment to truly MEASURE the ground characteristics, not with any useful accuracy. Plus, it's moisture-dependant, affected by what frequency you choose to measure it at, and not forgetting VLF's and PI's see things differently... I personally don't think air-tests are that useful, except for comparing MY nugget-smasher2001 with Bob in Australia's one. It's pretty easy to modify most detectors to give more air-depth ( increase RX amplifier gains for example ) but they won't produce gains in-ground.
  10. Quote:"The purists will tell me you have to compare the same element ...." Yes, that's the whole idea of a 'standard' target .... you use the same target, then the results become usefully comparable. Substituting a 'modern' .900 fine ( ? ) Napoleon coin with a 2000-year old quarter-stater made from electrum ( natural gold/silver alloy ) is not worth doing. I have to say that using ANY gold coin as a 'standard' is a poor idea. Test standards need to be low cost, or very low cost, so that anyone can readily obtain them, or several of them. I would be wanting a couple of 'test garden' ones, buried at decent depths, in different locations; maybe one tilted heavily; one for air-testing; a spare to take out in the field for impromptu in-ground tests. If they cost more than 5 US dollars, they are too expensive. Tom Dankowski seems fond of using a 1 Dollar US coin from the 1850's as a 'difficult low conductor' test standard. Not only is it gold, it's old and collectible, so commands a price premium over it's bullion value. I went to the trouble of designing and making a 'fake dollar', that was pretty close to the real thing, and could have been reproduced by anyone with some engineering skills. A better idea is to choose a circulating coin that has comparable characteristics to a small gold coin. There's plenty of small cupro-nickel coins worldwide; my 'favourites' include the Norway/Sweden 5 Ore from the 1980's ; the New Zealand threepence from the 1960's; the UK sixpence from the 1950's/60's; the UK 5 pence from 1990's/2000's.
  11. Quote:"I don't know how there can BE a "decay" if there is no "break" in the transmit" The FBS waveform consists of a burst of 8 cycles of 25kHz ( taking 320 microsecs ) followed by one cycle of 3.125 kHz ( taking 320 microsecs ), then repeat. Note: these are NOT sine-waves, they are SQUARE waves, of 50/50 duty cycle. The single cycle of 3.125kHz is split as quarter-cycle / half-cycle / quarter-cycle. This middle half-cycle is, I assume, where the 'Pseudo-PI' / time-domain stuff takes place, there is a 160 microsec 'break' , long enough to make use of it. This doesn't exist on the SMF Equinox waveform, there's barely 10 microsecs before the next edge transition, thanks to the 39kHz component of the transmitted waveform.
  12. Economics? The general public want it cheap, so industry-standard Imperial sized aluminium tubes are an obvious choice. But you have a point about the packing aspect. Even with simple tubing, they could put more thought into the design. There's examples of machines that break down into 3 sections ... that's good. Except one is long, one medium, one short .... not really a recipe for optimum packing. I've also noted that other aspects of the mechanicals are poor, too. Making two huge 13mm diameter holes in a 22.2mm tube is awful engineering, especially at a high stress point. But two manufacturers have done this. And both have seen failure of the tube as a result.
  13. But, how do you know they DON'T optimise ? Modern machines like the ML Equinox have a 'security chip' that would/could identify itself as: "Genuine Minelab 11 inch DD coil here". This info is read by the main control-box brains, so there's no reason it couldn't adjust to compensate ... increase the 'gain' on a small coil ( decrease on a large ) ; use different depth gauge calibrations so they stay true regardless of coil size ; change recovery speeds, maybe, or filtering time-constants. And obviously, the XP Deus coil has plenty of electronics and micro brains inside it as standard, so clearly it knows if it's a 9" elliptic DD etc, it's programmed into it during manufacture. Hence a large coil can be programmed with data about gain settings, or possibly the analogue side of the electronics has a few component changes affecting amplifier gain. However, it's pretty obvious that most machines don't have this ability. Any machine with a 'dumb' coil, with no integral amplifier or ID micro-chip/serial ROM, is unlikely to be coil-type aware. However, some of the older Minelab's, like the Sovereign, etc have a pre-amp internal to the coil. There's no reason why the gain couldn't be modified to suit the coil size/shape. They have been reverse engineered, so the info is out there ... perhaps the electronics is identical between coils, I haven't studied the details.
  14. I hear the new machine's successor is to be called the Diamantecore. As well as having some extra technical features, it is decorated with Swarovski crystals.
  15. Re: the Pseudo-PI technique used on FBS machines, this thread should explain: https://www.detectorprospector.com/forums/topic/13202-ctx-4040-or-equinox-1000-or-both/?do=findComment&comment=133265
  16. 'Burnt coil' first: The power put into a detectors coil is VERY small, 10's of milliwatts, enough to light an LED, for example the little red 'standby' light on your TV. So even if this power were increased +50%, it would still be a pathetic amount of power. Nothing will burn, burst into a mass of flaming plastic and copper, explode etc. So any suggestion that Mandingo is capable of such havoc is baloney, and is likely a failed attempt at 'hype'. Only two things of relevance come from "+50% more power": A potential improvement in EMI handling. If there's 23% more voltage on the TX coil, there's +23% more return signal from the target and the ground .... but the EMI signal remains the same. Hence a modest improvement in signal-to-noise ratio, which is useful. Increased current drain on the battery pack. However ... the Eqx draws about 420 mA, from a single Li cell, say 3.8V, hence 1.6 Watts. Of which less than 0.2W [my estimate] is spent driving the coil , the rest is microprocessor / ADC / signal amplifiers / LCD screen/ audio amplifier / wireless TX/RX etc etc. So the new machine will be similar; most power is the inner workings, the 'enhanced' coil power is not a major contributor.
  17. All this talk of "burning out an Eqx coil" is just a steaming pile of horse manure. Please stop it. A more pertinent question is: What is Mandingo doing that the Eqx didn't do ? Here's the Equinox transmitted signal: "The Equinox transmits a complex square-edged waveform, that repeats every 385 microseconds.[ 2600 times per second]. In that waveform are 15 cycles of 39kHz, 7 cycles of 18.2kHz and 3 cycles of 7.8kHz. That is how the operating freqs are related to each other : 7.8k : 18.2k : 39k are ratios of 3 : 7 : 15." This, as it stands is pretty good for: general detecting; low-conductor targeted detecting ( gold jewellery / ancient coins ); nugget hunting. The obvious weaker area is the lack of lower operating frequencies, which should ideally suit the high-conductor coin hunting niche, and potentially be useful in salt-water. The Deus2 can be seen to vary its MF frequency selections depending on mode, for example "Deep HC" uses a lower frequency mix ( 4.76 kHz & 14.3 Khz ). So it's not unreasonable for Mandingo's freq blend to be variable - that alone, I think, is sufficient to warrant badging it "Multi-IQ+". However, there is the X-Y display showing on the LCD screen. If this is anything like the FE/CO FBS system, it requires one l..o..n..g transmit cycle in its waveform to perform a 'Pseudo-PI' transmission. This is not possible with the Eqx's Multi-IQ waveform, there's simply too many high-freq signals in it. One possibility is they have created a mash-up of FBS and Multi-IQ. If the above waveform lasting 385 microsecs was alternated with a single cycle of 2.6 kHz, there would then be enough time to do the Pseudo-PI, and hence generate the "FE" signal of the FBS system. FBS uses a single cycle of 3.125kHz, so 2.6kHz is similar enough, and probably slightly better, at allowing this 'trick'. A down-side of this may be that there will be a slowing-down of the performance, much like the CTX is slower than the Eqx, due to the main TX waveform only being transmitted half as often. So it may be a user option: if you want 'CTX-style', you get slower response, if you choose 'Eqx-style', you get the speed.
  18. Quote: "Mr. Lawrie clearly stated .. Minelab redesigned the handle so it can hold TWO 18650 3.7 volt lithium ion batteries........as opposed to the one 18650 3.7v in the Equinox." Correction: The Eqx has a single 26650 cell: this is 26mm x 65mm, so it's fat, but not using up much of the available length of the handgrip. I did propose they used a single 21700 size cell in the "New Equinox" , as that has comparable performance to the 26650, but suits a handgrip shape better. However ... you guys are failing to understand modern electronics. Voltages can, and ARE, routinely stepped up, stepped down, inverted, to suit whatever are the needs of the appliance. If +5 Volts is needed, that can be created from a single Lithium cell. If +10V and -10V is needed, it can be done. Etc etc. So whether a gadget uses one Li cell or two or three, or a pair of 1.5V alkaline cells, it has essentially NO relevance to the power consumption / performance / whatever. ( plus .. two cells can be series or parallel-connected. It wouldn't surprise me if ML have the two 18650's in parallel, and are keeping as much of the existing Eqx circuit design as possible. )
  19. I'm with those who consider "50% more power" mainly a marketing thing. However ..... The 'Power' put into a transmit coil is a perfectly measureable characteristic, and it's nearly all heat in the copper windings, hardly any is truly transmitted into the ether or the earth/soil/dirt. And it's usually in the 10's of milliwatts for single-freq machines, and likely below 50 mW even on MF machines like the Eqx. And if you apply more volts to the coil, your power supplied to the coil goes up. A "50% increase" works out as 23% more voltage ( and 23% more coil current ). This could help in the quest for more depth, but is also beneficial when dealing with EMI , probably the more useful thing about it. And the effect on depth ? Boring mathematics about magnetic field decay ( inverse cube response ) tells me the expected air-depth gain would be +3.8% . This assumes the same receiver gain, etc etc., which is very unlikely to be the case - it's a new machine. ------ I think it's likely that what makes the 'plus' in the Multi-IQ+ is such things as completely different operating frequency selections, depending on the mode choice. This is a perfectly reasonable thing, and one XP chose for the Deus2.
  20. Many modern detectors use a fair bit of analogue front-end processing, then a modest microcontroller to do further signal processing. So there's a point where you'll find typically two demodulated DC signals ( Resistive and Reactive components ) , ready to feed into an ADC, probably 12 - 14 bits resolution. If your hardware piggybacks onto these signals, eg. possibly Arduino type sub-systems, you should be able to achieve your goal. And I recommend you sign up to the Geotech1 forum, where there's plenty of technical info, such as schematics of many detectors that could be the starting point for your project. There's also the thread "Let's build a PC-based detector" , which may be interesting to you: https://www.geotech1.com/forums/showthread.php?14102-Let-s-made-a-PC-base-metal-detector-with-usb-interface-!!! The general Geotech forum index: https://www.geotech1.com/forums/forum.php
  21. Fellers? I'm just one, not a consortium. Best depth is achieved with disc set to Zero or 1. Set Disc to about 11 if you want to lose lots of depth... maybe if you have bad EMI, it could help deal with it, as an addition to lowering the sensitivity.
  22. To get to the 'disc mode', you need to press the mode button until the highlighted option is the top-most one. Then turn the rotary control counter-clockwise one click, and the disc mode is highlighted. Then the mode button will cycle through the left menu. The 'notch' feature is a mess. Poorly designed, poorly documented in the user manual. And you can't assume " Well I never use it, so it's not an issue" , because it's very easy to inadvertently put in some notch. Then the problems start. Thankfully, a simple solution exists: Factory Reset. Learn and relearn how to do this, and 'notch nightmare' is not a problem.
  23. Ferrites are shinier and silver-grey colour. They are normally extremely hard, you can't abrade them; scratch them with a knife, you get a silver steel streak on the ferrite. Powdered iron is duller and blacker, and is medium-hard. With effort, you can scrape off small bits, and strong abrasives like silicon-carbide paper will remove it. So the ML ring is powdered-iron. The colour isn't very informative ... they might just have painted it black themselves to hide the manufacturers part marking. The 'Doc' toroid seems typical of ferrite: shiny, hard. But ferrite is almost always electrically non-conductive, though I have read about some that will conduct ... I have no idea what type. 38 Ohms is surprisingly low. Again, color coding is hard to interpret .. yellow with one white face is typical of Type 26 ferrite blend. Edit: It is the very-high mu ferrites that are electrically-conductive ( mu over 5000 typically ), and I've just measured one example ( probably mu=15000) in my 'bits box', and it reads 200 Ohms across its diameter. That may be indicative of the 'Doc' ring material. Jason: Do you have an inductance meter? Wind 50 turns of enamelled copper wire on each toroid ( diameter 0.15 to 0.6mm, not important ), and see what an L meter gives. I guess the ML one will measure about 30 microhenry. The 'Doc' sample may be anything, up to 20 millihenry.
  24. A few observations from an electronics guy, who has used these toroids. There are two distinct 'types' of material used in these toroids: Powdered Iron, and Ferrite. 'Powdered iron' is ultra-fine iron dust, that is produced by chemical reaction, (rather than mechanical grinding etc ). There are some similar nickel-iron alloys ( eg. Permalloy) and other exotics like Sendust that can also be considered 'Powdered iron'. 'Ferrite' is non-metallic ( officially a ceramic ) that's essentially rust ( iron oxide ) with small quantities of metals like zinc, manganese blended into it. This is turned into fine powder by mechanical grinding, and then moulded. They have quite different magnetic properties. Powdered irons have low magnetic permeability, (mu), typically varying from 1 to 100. Ferrites generally have higher mu, from 50 up to 15000. Minelab specify a low-mu powdered-iron toroid, not ferrite, for detector balancing: Quote: "A ‘dust iron’ toroid suitable for the HF frequency band (e.g.1–30MHz with an initial permeability of between 6 and 10) has been carefully selected." Regarding colour-coding: It's primarily a powdered-iron thing, even then, different manufacturers have different coding, and there's plenty of different materials/blends that it's not worth trying to identify a toroid by colour. Magnetic testing will tell you much more. Ferrites have no useful colour-codes, and are often unpainted, as they are naturally corrosion-resistant. So if you're wanting to self-select a toroid for detector set-up, you want permeability, mu, of 6 -> 10, and a physical size that's vaguely the same as the ML suggested type, though it's not critical. For reference, here's Amidon Corporations data sheet for ferrite and iron cores ( pdf ) http://www.amidoncorp.com/product_images/Amidon-Tech-Data-Flyer-v19.pdf
  25. I see the word 'Quartz' among the 'metal type' list ... a bit of a red flag to me. It makes me wonder if it's related to some kind of 'esoteric' detector , the kind that have five radio antennas on them, and a bottle of Gypsy Tears inside the handle.
  • Create New...