jasong

I totally forgot about this detector. I hope they come out with one still.

All I need is: light, fast, quiet (EMI), external speaker, and a little more sensitive than a 5000 so I can hit the buried sub-0.1 nugget leads while exploring. Make it $2k And I'll ditch my 6000 and use this all day as an exploration/prospecting machine and never look back, I need an excuse to stop using ML products, still pissed about the 6000 honestly and how they treated the EMI issues and fix "rollout" that I had to force for them. Plus I just don't trust the 6 anymore either.

I had a bad experience with Nokta when they first rolled out the FORS Core, 3 of mine failed in a row and I just gave up and threw it in the closet. Willing to try again. 

Either galena or chalcocite probably. Lead and copper sulfides. Maybe hematite, but less likely. 

Chalcocite can hit quite hard on a VLF detector and sound much like gold.

I've found both occurring in gold areas in the past. Galena and chalcocite should have a faint odor of sulfur if you crush/scrape some of the rock, hematite will not smell of sulfur. If smelling of sulfur, a density test will tell the difference as galena is 7.6g/cc and chalcocite is 5.6g/cc. 

Horn coral fossils

Are you aiming to cover ground or aiming for depth on patches? Seems to me those large drag coils are mostly for depth on patches and not ground coverage, especially not being towed. But maybe I misunderstand them due to not having used one.

I tried a 25" round and gave that up as too large for exploration because it was slower to swing and produced too many spurious signals that caused lots of lost time investigating, and investigating each target was laborious due to coil size. So one even larger seems like it may come with the same problems for covering lots of ground. 

You probably already know about these NF 30x7" Patch Pros and eliminated them, but here's one if not - swiped this from Rob's site. I haven't tried one my self so take what I say with a hefty grain of salt. If ground coverage is the key and not depth, then more elliptical is better (large swath coverage, but skinny so quicker to locate targets, less EMI per area swath coverage). This one has the area equivalent to a 15" round roughly, so the EMI should be about equal too, and a 15" is ok for exploration IMO. The EMI/spurious signals on coils like 20 or 25" rounds increase quite a lot (especially on uneven ground where the coil is at an angle)...on a big drag coil it seems like you might be chasing ghosts often all day, and that means less ground coverage. Just a guess though, I could be totally wrong. And we definitely have worse EMI issues here so that may just be a big problem for us and not for you. 

The other consideration is if you are working salt ground then you want to minimize your total coil area too, and in those cases and extreme elliptical shape is the best too since total coil area is small relative to swath coverage. 

Just another thought to toss out there anyways.

I've never built or run one myself. I hope I can meet up with Chet again sometime and check one of his out or maybe give it a go in person and learn a bit more. Until then I can't really comment with much useful.

I definitely relate to the "big country" issue though. It can be an overwhelming amount of land to cover. Barring a better solution, the only ways to tackle it for me have come down to 3 things basically: speeding up by using a lightweight, quiet, fast detector (I've posted about this technique a ton, but it's not for everyone granted). Geologic/topographic indicators. And using an ATV to speed up movement between low probability zones, as well as to do a lot of scouting by eye first.

I'd say at least 50% of my field prospecting in big country now is standing on my ATV while driving and just looking at the ground with my eyes, or getting from the most likely place to the next most likely quick without walking or detecting in between. I'm missing a lot, but I'm also usually only spending time detecting in the most probable spots when there is just too much ground to feasibly detect.

I'd love for there to be a better solution...starting to look unlikely we'll get one though. 

35 minutes ago, Calarms said:

What wavelength UV light

The one I used in my pic is 365nm.

1 hour ago, Jim in Idaho said:

Yeah...I noticed the hex in the pics, too. Don't know why I didn't notice that before. The Grossular garnets are the only ones that fluoresce, and I'm not sure all the colors of them fluoresce. I'm thinking tsavorite grossulars don't. I need to look that up. I'm thinking, because of the nearly identical colors, that both of our gems may have come from the same source. Hausel mentioned a creek in the Wind River range that had rubies. I forgot to post this, so after some research it looks like the only grossular garnets that fluoresce are from Quebec, and Tanzania, and are clear under natural light, so mine probably is a ruby....COOL!..Thanks, Jason. Now I need to go down in the gem room, and try to find it....LOL

Jim

Yours is about the most gemmy one I've seen from Wyoming, probably worth prospecting for a lode source on that. Most the WY rubies I've found or seen have been very low quality - shattered and bad color. 

This UV flashlight I have is crazy powerful, I'm going to take it camping this summer and do a few night scouting trips just out of curiosity. That red stands out so starkly it seems if there were rubies around they'd be pretty easy to spot. It's easy to tell the difference between that red and the reds from calcite. 

Interesting Jim...yes mine came from Wyoming too, though not from any of the diamond areas in the Green River basin. I can't quite say where this one came from yet, but I hope to be able to write a bit more about it in the future as there are some other pretty interesting things associated with it.

Yours is an interesting one though...pictures can be deceiving so maybe I'm not looking at it right, but it appears to have a semi-defined hexagonal form? If so, I would lean more corundum - probably ruby - than garnet. I don't think garnet fluoresces under UV much either. I think you got an interesting one there...it's more gemmy than mine is too. 

Can't miss that red glow... Granted this one is tiny and not really gem color.

Was storing some samples and checking them out in the microscope first, and decided to run the UVBeast flashlight over them. This one came from a place with no known ruby occurences, didn't expect to see this turn up. It could also be spinel, but no known occurences of that where this came from either. 

Might be worth running a UV light over panning/sluicing concentrates for people that have them. Never know what you might find...

I wasn't really shooting for any kind of accurate number, I just wanted to show the physical relationship between coil inductance, material permeability and number of turns in a quick example. Just to show one might be able to replace some amount of copper wire with a lesser weight of ferrite. No clue though.

I guess it would really need to be something done via experiment, or done in EM finite element analysis modelling software though to know if it worked. Hysteresis as well as localized magnetic flux concentration around the ferrite might make this infeasible in a PI, GPZ maybe not? The flux concentration effect might be interesting to experiment with too though on it's own for various reasons too. 

I guess I'll chunk it onto the log pile of ideas I'll never get around to actually trying. 😄 One of these days I'd like to get back into electronics again, just no time now. 

I don't mean a solid ferrite core, I just mean adding some small amount of ferrite to make up for the inductance loss resulting from subtracting some coil turns. Maybe even just using ferrite powder in a paint as shielding instead of graphite paint could be enough, no idea. 

A little bit of highly permeable material can raise the inductance quite a lot.  Permeability of air = 1. Permeability of ferrite can be around 1500. 

So for a solenoid inductance would be something like this:

So adding a ferrite core would increase the inductance 1500 times over a foam/air core, which is way too much because we'd need to subtract a substantial amount of windings to get back down to 300mH.

But if you just added a small bit of ferrite so that the entire coil "sees" an average permeability increase of maybe 25 (since much of the foam or air will still be permeability = 1, the total permeability will depend on the size of the ferrite), then you could remove quite a lot of copper. The ferrite might actually weigh less than the copper did, and the coil could be lighter? Less turns will mean less resistance, so the remaining turns could be downsized in gauge diameter to increase resistance again, and this too would save weight. 

Just a quick example: Foam core, 1 cm thickness, 10cm coil radius (8 inch wide) means you need 275 turns of copper to equal roughly 300mH.

Conversely, add a bit of ferrite in some way or form to increase permeability to 25, at least in terms of what the detector sees (this would be a small amount of ferrite) and now that same coil dimension only needs 55 turns of copper.

(I have no clue if this is close or far from actual ML coil turns, I'm just using a generic example with the formula above)

In this example the ferrite would probably weigh less than the 220 turns of copper removed from the coil since the ferrite permeability is 1500, you wouldn't need to cover the entire core to reach an average permeability of 25.

No idea if that would work or if the hysteresis curve of the ferrite would screw the detector sensitivity up. Curious though. A high permeability material with a slim hysteresis curve might exist? 

In the case of the smaller coils lacking space for the windings, is it possible to get rid of some windings and then raising the coil inductance back to 300mH via the inclusion of a small bit of ferrite or even iron to boost it back to spec? Maybe using the ferrite for shielding in some way too such as powdered ferrite paint instead of powdered graphite paint (2 birds, one stone)? Permeability of ferrite is like 1500x that of air, foam, etc so it shouldn't take much to raise the total coil inductance - at least in terms of the inductance the detector sees.

If that works, would adding materials with varying degrees of magnetic permeability to increase inductance be a potential experiment to reduce winding weights and thus total coil weights too? Or would those materials themselves have a negative effect on the detector operation/ground balance/etc? I wonder if in some way this is one reason the ferrite was included with the GPZ due to some kind of design considerations like this?

Slightly smaller diameter wire could be used to increase the coil resistance if reducing the turns/wire length threw it out of a critically damped state and introduced ringing? Or I assume they are designed to be critically damped anyways, but I guess I'm not sure.

I've never built coils for detectors, but I find it interesting to think of experiments to try to potentially improve upon them. It's educational to see some discussion of it here.

For the smaller concentrics, is it possible to have enough space for flat windings in a smaller coil by stacking them on top of each other into some kind of quasi-concentric? Or does the produce capacitance issues? Or it wouldn't really work as a concentric (since they aren't technically concentric)? Would that arrangement be useful at all for something, or no?

Woody's talking about cable capacitance also makes me wonder if XP has the right idea at least in part by putting the RX circuitry in the coil itself. That way only the TX would need a cable from the control box and the capacitance of the cable shouldn't matter since the RX isn't passed through it. That should allow a quicker sampling time, and thus more sensitivity to faster transient targets, etc. Curious if Minelab might look at that idea in future gold detectors, or if it's even feasible with PIs. 

2 hours ago, Reg Wilson said:

Back in 1990 I was sharing a house with John Hider Smith and Ian Jacques just out of  Maryborough in central Victoria. We were involved in testing a new type of metal detector called pulse induction when Bruce Candy paid us a visit with an experimental system that he had been working on. This involved a large cable that would loop around a patch of ground that was suspected of holding big gold at a depth that conventional detectors would be incapable of hearing.

The idea was to have this Tx cable connected to the electronics while an operator would work within the circle of of cable with what appeared to be a conventional hand held detector, but would only be Rx. Hopefully the Tx would be powerful enough to induce a strong electro magnetic field within the loop, while the Rx would pick up the target response when passed over it.

My memory is a bit foggy on  the results, but for whatever reason it was not a 'goer'. In those days Bruce was always thinking of new ways to achieve results.

Ah nice...Candy's idea there is exactly what I was thinking about myself. Bummer it doesn't work. I'd be curious if you have any old notes from that experiment what the problems were and if they were surmountable. I'd see it being hard to sell and limited customer base, if that was the problem then I might try myself, but if it has physical/engineering problems then there is nothing I could do any better than Bruce Candy did so no point trying.

Interesting to hear it was tried though, thanks. 

43 minutes ago, Chet said:

    Large coils are on the back burner for now. Below is the second one 58" x 28" that I put together. The electrical specifications are the same as standard coils. I wound both the transmitter and receiver with wide spacing between turns. This cuts down the coil capacitance and improves the Q (quality) of the coils.
    It started out to be a drag coil but since I don’t have a ATV and Northern Nevada has so much sage brush it became a large push and pull coil. It weights approximately nine pounds. It has some serious problems that prevent it from being a good coil. My pick, the detector body and other stuff are too close to the coil. Going over rising and falling ground sounds similar to swinging over damp salty ground. The coil cable sounds off when it is moved up and down. The windings are glued down and the foam board is rigid so it doesn’t have any bumping noise.
     It picks up shallow .22 bullets as double hits as each receiver coil passes over them. Air testing above the coil; one ounce gold coin around two feet; coke can approximately seven feet.
     Since coke can size nuggets are so rare I am working on 25 to 30 inch coils. Improving depth on one ounce and below is the goal.

That's awesome Chet! Haha I love it...even if it didn't work as you'd hoped. The spirit of experimentation is great. Don't ever get rid of that coil, I'll take it if you are going to throw it away! 😁 👌

Yeah it's hard to find a place to imagine a drag coil being able to be ultra useful due to all the brush. I'd like to try dragging one down some of those Gold Basin deep washes where I know some larger stuff came out of, just flat sandy 4ft wide washes, all about 2-4ft deep. I had a backhoe in one wash and I was hitting deep little pockets that had nuggets at like 5-6ft deep, but they were like 2 grams max. Unfortunately most of the big nuggets I know of came out of washes you can't run a coil that big, but there are a few... I know a few places where some 4-10 ouncers came off hillsides that are kinda deep too, but a bunch of people pretty much claimed all that stuff after Jeff Williams came in and started doing gold tours on all the old dead patches like a dodo. 

How deep will that 58x28" hit a .22? Mostly just near surface? 

I have the 22" X Coil CC that I'm dying to try out, but all my ground this summer is not very deep so I might have to wait until winter to really give it a workout in NV or AZ. 

I'm glad you are still working on the big drag coils, I'd really like to see one of those in action sometime if we happen to be in the same place and same time again. One of those would be fun to drag around some of the washes in Arizona that are deep and produced some bigger nuggets. 

I have my old 4500 still and I'd like to put it to use for something like that eventually, rather than just sitting in the closet. 

Is there any consideration for those big drag coils other than just getting the electrical characteristics (inductance, resistance, internal capacitance, etc) matching within some tolerance, proper shielding, and then plug them in and they should work? For the drag coils I imagine you have to find a way to keep them pretty rigid still?

Ah bummer... it's no fun to lose something valuable, but losing something with valuable memories is the least fun.

After almost 30 years of managing to hold on to the first rock hammer my mom gave me when I was 7 years old (despite losing probably 8 or 9 other newer hammers), I ended up leaving it in Colorado on the Gunnison River. Drove back the next day and it was gone forever. Those items are just so much better with the person that lost them than anyone else. 

I hope you are able to either find your pack or someone finds it and returns it.

Wasn't there some statement a year back that X amount of new detectors was set to release in fiscal 2023 by Minelab? Did we already hit X or are they falling short of whatever that number was due to market declines? I wasn't counting or keeping track, but I'm curious now. I thought one was likely to be the GPZ successor, or maybe just hoping. 

Thanks, meant to say ELF not ULF. Do you suppose a really large ore body might alter the phase...or some other quantity...of an existing ELF signal passing through the Earth already and detectable at surface too, around a large ore body, such that it could be detected with an RX loop? Or something like a gradiometer where one RX loop is separated from a 2nd RX loop by some distance in order to detect changes in the ELF signals passing through the Earth in different spots? Like would it be doable using just existing ELF signals, or would a local TX module be required to have enough control over the TX signal shape/power/etc?

Also, what do you suppose would be the theoretical limit on coil size for a standard PI type detector, before the signal simply gets too weak for nuggets? 5ft? 25ft? 100ft? What about doing something like pulsing a bank of 1000v low internal resistance caps through the coil, using beefy wire like 8 gauge stranded or something that could take the massive current pulse? That should compensate for the large coil size up to some point.

I'm just curious if there is a way to move specifically beyond the coil on a stick model. Or also, if you could remove the TX/power circuitry from the hand held detector itself, you might be able to just get an ultra quiet noise floor and ultra sensitive RX unit, very lightweight lacking all the power circuitry, and use that alone by hand.

I have a wacky idea on the submarine topic - ULF frequencies used by subs and also emitted by certain natural phenomenon are known to travel a good distance through the earth itself and detectable inland like in Colorado and whatnot. Would there be a way to use those existing transmission already deep in the earth as "TX", and just use a lightweight "RX" handheld unit, or even a truck mounted loop? Obviously not for small nugget size targets, but maybe for larger conductive ore bodies for geophysical exploration?

Similarly, would it be possible to build a massive "traditional" PI by running 4 stakes over like a 500ft diameter square, then winding a coil over the stakes and using that as a TX mono. Then using a lightweight RX handheld unit that senses the pulse timing for synchronization, use it to scan for really deep targets that are nugget sized? Or potentially a drone or atv mounted RX loop that might not need to be so close to the ground since the TX loop is so large?

I'm curious to experiment with stuff like this that I've thought about for a while, but I just never have the time or resources to try. 

2 minutes ago, Chet said:

       In my days of working with cryogenically cooled radar receivers we had a constant noise/EMI problem that we could not fix. It was the distant noise/static from the big bang sill travelling through space.   
 

Familiar with that story, it was and I think still is required teaching before starting the chapters on the discovery of the cosmic background microwave radiation that ended up having a significant impact on cosmology and physics. 🙂

A lot of science has been discovered by accident like that. It's why I always try to be hyper in tune with an odd observations, most are nothing. But occassionally....

Try facing your phone screen towards the control box, on the right hand side of the box. My phone sets the detector off every time if I bring it close to the box, but only within about 1/4" or less. I have an S22 I believe it's screen is different than the A10e though. If I do it with the screen facing away from the box it's much harder to hear. 

The carbon fiber doesn't help reduce that effect though - so I don't think it's EMI related. I think something in the phone screen is electromagnetically coupling to something inside the control box. Oddly though, placing a large hammer or wrench to the side of the box produces no such effect, so I'm not sure what's happening really. I'd film it but my phone is my only camera right now, so that doesn't work. 

Also, the effect seems to be decreased now after the fix. But that could just be my imagination. I do seem to remember it being much bigger over more distance pre-fix though since I discovered it by accident just by my phone being near the box and not because I was pressing my phone onto the box intentionally like I am now to reproduce the effect.

Anyways, it's a minor effect, not really a hinderance to detecting. But it did make me curious to see if it was EMI related or not because if so, it might have been an easy fix to quiet mine down more if the same mechanism was also potentially allowed additional EMI from other sources in. Even after the fix, mine can be quite noisy in some locations which makes me think (like your helicoptors) there may be localized EMI sources that are present 24/7 for me, so I was hoping to see if there was some easy way to increase the shielding. I'd really have to try out in the field though to see if it makes any difference, and there is so much snow left here that it'll be a while till I can get out. 

In my head I wanted something simple like making some carbon fiber stickers to place on the side of the box or on top of the coil as basic shielding enhancements, but it doesn't appear so far that this will be much help. It was worth a shot though, and I'm definitely going to test again when I get into the field into a much quieter environment where everything isn't being blown out by 60hz. 

Got my carbon fiber today, it's a roll of fabric itself. Not sure what the actual resistance is because I'm stuck using a really cheap multimeter right now, it's saying 5 ohms/inch but I don't put a lot of trust in it. The 6000 coil screams on it when I drape it directly over, then rapidly dies down and stabilizes.

Anyways a few interesting things - It doesn't seem to degrade the sensitivity, at least on a US quarter. Or if it does, it's minor. This was just a real rough, brief test though just to see what happens, nothing more. 

But, it seems to me that you might actually be able to build coils out of carbon fiber where the case itself is the shield, and potentially save some weight by eliminating the coil cover if the resin was stout enough. If it was just 1 layer of carbon fiber, the coil might be lighter in general than plastic coils too. Might not be worth the potential increase in knock sensitivity though.

But interestingly - carbon fiber didn't appear to redcuce the EMI as I hoped. Which means it's either not acting as any better shielding than the graphite paint already is, or that the EMI is mostly still self generated.

That, combined with the fact I was testing inside a large metal building that itself is shielding a lot of external EMI like a Faraday cage (my cell phone almost doesn't work inside), makes me wonder if some or even most of the random chattering I'm hearing on the 6000 post-fix might still be internal/self generated EMI too (and presumably this EMI could be improved with a mod?). I'd have to experiment a bit more to see where it's coming from though.

Chet, what I'm wondering though is if lower resistance shielding might work on the GPZ since that copper was working for him. And if so, if lower resistance shielding might actually be more effective at cutting more EMI. Woody said it worked on the GPZ but not the 6000. 

He appears to have discovered the 6000 EMI/speaker issue too now. He hasn't quite made the connection yet though. I told him about the fix, I'd be curious to see what he thinks about it and if he can improve it more. 

One thing I'm curious also to try is I'd like to cover my 6000 box with carbon fiber, and see if it lets me carry my phone next to it just as an experiment.

Good to see you around posting again Chet.

Curious what you think about where Woody is able to throw a solid copper fabric over the GPZ coil to cut out noise in his house during testing, yet is still able to detect targets through the copper mesh without much decrease in sensitivity? Did you see that part of his video? That must mean the GPZ works differently enough that you can use a more conductive shielding? It didn't work when he tried it with the 6000 though.

I'm wondering about it because if a solid copper fabric on top of a GPZ coil works, then should we be able to make coils for the GPZ out of carbon fiber (which is conductive)? At least, on the tops and sides, if not the entire coil. That may lighten and simplify the GPZ type coils if so. It may also be a magnitude better/more effective shielding than high resistance graphite paint is.

I ordered a sheet of carbon fiber to test with out of curiosity, but the mail has been crazy unreliable into Wyoming due to all the snow/ice road closures and this one seems to have gotten lost in transit, so waiting for a replacement.

2 canyons over is just as flogged as anywhere else now.

If you really like remote, undetected places with small chances of finding gold, but often little trash, try some raw exploration. If you spend a year or two doing that on your own, and show you have the patience to keep at it, as well as learn how to be successful at it, I'm looking for someone to work with occasionally. Projects where the amount of land to cover via just raw GPS gridding/mapping, daily detecting as if it were a job, low probability of nuggets, and remote living requirements usually mean no one else is interested since it's not really what most envision when they want to do relaxing nugget shooting. You'd really have to show you can bring something to the table though in terms of developed skillset too, not looking for weekenders or greenhorns. 

Something to consider anyways.

4 hours ago, Medina said:

ok, my .02 as a new to minelab customer, was a garrett whites sorta guy

IF you stick with Minelab and they do make a good product, as good as any company, when they announce a new..whatever, new metal detector, Immediately,  sell your old one.  ASAP

after they talked about releasing the 800, the weeks following the "unboxing" and find vids, the Etrak prices dropped (so I bought a new in box CTX, two coils, harness, books for 1500) in the weeks following the release (talk..of release) and vids of folks diagnosing performance based on the box cover and grainy photos, used 800's dropped a bit..then when they actually dumped the 900s and still did the carrot dangle trick with the manticore, used 800's were going for 500 bucks, CTX's are way down as well. When the announce the release of the CTX4040 or whatever it'll be called, dump your manti's and prepay obediently!! 😁

it was cool they made the 900's take the 800's coil, I lost less money selling the two 800 coils (percentage wise) than I did selling the 800. 

just a heads up..I'll have a Manticore for sale when they do announce the newest CTX... I dont have a problem, I can quit needing the newest metal detector anytime. yup.  

I was just looking for a used 800 for cheap and actually I'm pretty surprised there doesn't seem to be much out there. Did all the 800's sell quick, or did a lot of people keep theirs?

The only used ones I can find, I can get for about the same price new with a discount.