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GPZ 7000 Tear-down


phrunt

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Proper shielding and isolation is like design 101 for sensitive radio electronics (like a detector). I can't convince myself that Minelab didn't know about this during design - I mean why intentionally put the power supply right next to the RX module?? It's not hard to put the power supply in it's own entirely shielded case and seperate board. It half makes me wonder if the intention was to produce a lower RX gain 6000 and 7000 using cheaper parts, then later models would come out with upgraded shielded components, lower noise, and a higher RX gain as a 6000 "Pro" and 7000 "Pro" using the same boards, or something along those lines, using substantially the same circuit but repackaged in a more modern ergonomic shaft/control unit. 

I guess probably not, since it's been 8 years since the 7000 release and doing a "Pro" style release could be done quickly. At this point, with that much delay between models, I'd hope the 8000 is something better. But I'm still left scratching my head.

*I agree with the noise cancel thing, but it sure is nice to have the illusion of speed on the 6000 quick cancel. What I'd like to see - given the power of the FPGA's today - is an automatic noise cancel that just always scans for the quietest channel in the background 24/7 so that you can switch to a quieter channel instantly if you want to.

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Also, thinking back to electronics classes, if there are that many unshielded and clearly noisy components on board then Woody's loop technique may not be picking up all the areas of potential self inflicted EMI.

Because the traces on the board itself may be acting as antennas and injecting noise into the circuit as well. Another reason it's best practice to shield and prevent self induced EMI, it might show up in places you can't really see by just probing with a loop in open air.

For instance he probes near the RX module and thinks the inductor EMI drops off. But if there is a trace in the board closer to the inductor, which also leads to the RX module, then the RX module could see higher amounts of injected noise from the trace than he sees with the loop.

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His latest video he seems to shield all the self generated noise out of the 7000. Goes on to say someone sent him a 6000 to work on (he surmises as I did earlier, that it suffers from the same problem), and might try an Axiom. Then mentions some rumor about a new upcoming detector release being basically the 7000 put into a 6000 case.

I'd post the vid, but man these things are hard to watch and I don't want to post a link to a bunch of camera fidgeting and dead time. I really, really wish he'd spend a bit doing some basic editing. Because he does seem to have some interesting things to say and show.

Also drives me crazy he does all this work on noise reduction, then demonstrates it in a noisy room in a house with some copper sheet over the coil, using a 9V battery as a target (bad target selection for a number of reasons), with his belt and microphone moving right next to the coil too.

I find it pretty interesting the detector still detects a target at full depth through that copper fabric shielding though. That's basically a faraday cage. It must be detecting some kind of steady state EM properties, anything transient should be getting blocked, or I guess just fields directly coupled rather than radiated at least. But it does beg the question - can we do better with shielding on coils now too? That'd be the next thing I'd look at, almost curious enough to go put some aluminum tape on the top of one of my coils this summer whenever the snow melts off.

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If you put shielding tape on top of a GB2 coil the detector goes completely numb, can't detect a thing so it's interesting the GPZ can detect right through it.

If they put a 7000 into a 6000 case I don't want one, to me that's a downgrade as you can bet they'll change the coils to chip inside coil.  It needs to be significantly better than what I've got or I'm certainly giving it a miss, and I think that will be a challenge for them.  I don't care about ergonomics, weight, Bluetooth, whatever cosmetic things they can do to improve the 7000, I want real performance improvements over the 7000 with a range of X-coils and lots of them or it's a waste of money.

It's a wait and see, but if the 6000 is any indication of what to expect, I don't want one.  Performance differences from what I can see on anything are minimal over the 7000 if at all.

If Woody can improve shielding on the 7000 perhaps I'll take that path and send her off to be modded instead of an 8000.

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If it was nicer out I'd go do some experiments with aluminum tape. Still winter here though. The copper fabric oddity does bring up one more potential improvement - can we shield the bottoms of coils too for more EMI prevention? I wonder if there is much EMI coming up off the ground as reflection, ground plane transmissions, etc or no?

If the GPZ is using some kinda static fields, it gives me another idea - curious what would happen if you put some kind of steel on top of the coil.  Maybe a piece of thin steel sheet, maybe just some steel nuts/washers? Would there be a depth increase?

Reason I'm curious is because ferrous metals "enhance" or magnify static magnetic fields by concentrating flux, and higher flux density means a stronger signal. It would be interesting to experiment over the RX lobes, TX lobe, and both at once.

Would be easier to try on the 6000. I'd laugh hard if a quick hack to getting a little bit more depth ended up being taping a big steel washer onto a mono coil. ? 

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A bit like what some people do with their Carrots, this guy has a pretty good way on his Carrot with an antenna.

 

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Interesting, gonna have to try that too on my carrot, first I'm seeing that. Not quite sure what's happening there, but I think it's different than the steel-on-a-coil experiment I want to try, as those antennas are probably non-ferrous (and the pinpointer is a VLF).

Guessing there is some component inside the carrot about at the point the tip of the antenna extends out to, and it's coupling to the antenna and changing some component values by proxy on the board?

Hmm, some stuff to think about though.

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Tried some experiments with the 6000, got too curious. Putting steel on the coil definitely doesn't help, putting that right out front. ? 

But, it was informative, Geosense seems to be a bit too smart for it's own good sometimes. Was doing some air tests on a US quarter with various chunks of steel on the coil. It'd work, but clearly it was adjusting ground balance and reducing sensitivity as a result. I could get the 6000 to be absolute dead quiet in the middle of my noisy shop by putting a bolt on the coil, because it'd adjust the sensitivity down automatically - even in manual mode.

Or at least I assume that's what was happening? The depth on the quarter would go to almost nothing too depending on the amount of steel, with one large nut sometimes it'd be 70% depth, another time it was like chunked out at 40% giving me all or nothing overload, even after I removed the nut - just stuck there with useless depth. Probably some ground balancing happening there too.

It was unpredictable though, sometimes took a bolt, sometimes 2 nuts, sometimes 1 nut (was using 3/4" hardware). 

The problem is that once it adjusted down, even after I removed the nut it wouldn't adjust back always (or ever sometimes), even if I was in manual. Sometime's it'd stick me with like 70% reduced depth, other times it'd stick me at like 30% reduced depth. And when I rebooted, sometimes I was still at some odd amount of reduced depth compared to baseline. Like literally - I have a measuring stick with a 4" variation on the max detection depth of US quarter starting from reboot (with no steel on the coil). The lack of repeatability was concerning, because now I wonder if sometimes I sit on a surface nail too long and then go the rest of the day with a reduced amount of depth due to Geosense? Dunno.

Or is Geosense reducing depth independent of the steel and just adjusting sensitivity on it's own differently every reboot due to the EMI in the shop? 4" is a huge variance, lots of missed gold too if something is happening I don't know about in the field. We know hot ground kills depth, but are we losing tons of depth in noisy EMI environments too from Geosense?

I dunno. Hasty test. Read nothing into them. Just an oddity. I'm side eying my 6000 with a bit of suspicion now though. I need trust things are doing what I configure them to do. I missed a metric ton of gold (all 1 gram or smaller, within the 6000 wheelhouse) last summer with the 6000 that I got with the 7000. I know the 7000 is just more powerful to begin with, but now I'm wondering if something else happened...

 

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Yeah, after further testing, the 6000 definitely is having some weird highly variable automatic sensitivity adjustment thing going on under the hood (we knew this already) depending on EMI around it and also on prior exposure to big iron (3/4" nut for instance). Problem is that this seems to bleed over into the manual settings too, and it seems to sometimes exist still after rebooting even. Hard to tell though since there is no screen to look at the adjusted settings data.

The problem isn't that it's happening, it's that it stays. And is unpredictable. I mean, like 3-4" difference on a US quarter when I'm testing under identical conditions. That's too much, I can't not be knowing if I'm running 3" shallower at random times for the rest of the day, because I hit some big iron in a hole last target. Or because there was some EMI storm that went away.

Maybe I'm missing something here. Maybe it's just my machine. But I have some trust issues with my 6000 now. Honestly I'm not sure I have enough trust to keep using it. And I'm really hoping Minelab gives us an ability to turn GeoSense or automation completely off in whatever the 8000 is, and/or user ability to custom limit min/max allowed ranges for it to auto adjust sensitivity, etc within, and give us some on-screen visual gauge where we can see what adjustment levels it is at to verify, and a reset button for the Geosense adjusted settings.

Basically for Geosense: we need a "dashboard" like a car, that shows relevant settings levels so it can be confirmed how the detector is running. And we need some slider controls that let us determine the max/min levels Geosense is allowed to adjust each settings. It's too hard to trust this or know how we are running, without knowing. Total lack of control is ok for ACE250 level models, not pro models. 

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