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Tdi Pro Coil Comparison On The Goldfields


karelian

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I should probably test the DC resistance of this ML coil, and also the inductance, and see how those specs compare to a different mono coil made for the TDI. However, the Sadie is not made specifically, for the TDI, and it works great on them, so maybe it doesn't matter.

Jim

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2 hours ago, Jim in Idaho said:

I should probably test the DC resistance of this ML coil, and also the inductance, and see how those specs compare to a different mono coil made for the TDI. However, the Sadie is not made specifically, for the TDI, and it works great on them, so maybe it doesn't matter.

Jim

Though I have not yet received my 8X6 Sadie, from all the glowing reports, it's obviously well thought of.

Perhaps John's mention that it doesn't work as well on the TDI is more of a comment about the lesser ability of the TDI detector itself, rather than a degradation of the coil's ability when used on the TDI.

As Steve mentioned, the TDI is nowhere close to the abilities of a GPX5000. I haven't used a GPX, but I can only imagine the 6000 and 7000 are even better.

Interestingly John mentioned a quirk of the GPX6000 (I think he said) that I had heard about with at least certain PI machines. It is the tendency for them to completely ignore certain sizes or shapes of gold nuggets, finding larger, or smaller gold with no problem, but completely ignoring nuggets in the "donut hole" detection sizes. He mentioned he found this after thoroughly going over an area with the 6000 and cleaning it out, only to go over the area with the 7000 and easily turning the previously ignored nuggets up in depths easily exceeded by the 6000-it just was blind to them.

I wonder if the TDI exhibits the phenomenon with certain target sizes? I don't have enough experience with it to have a clue.  

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Yes...the TDI manifests the same issue, and to a greater degree.

Jim

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4 hours ago, Jim in Idaho said:

Yes...the TDI manifests the same issue, and to a greater degree.

Jim

Is it known what size/shape range it ignores? Or does it depend upon the coil used more than the machine itself?

Is it a function of the delay I wonder? It would be interesting if there were a way to "sweep" the delay, so that you could have it rapidly sweep +/-  20% above/below the selected delay setting. I've read that even the difference from 10us (the optimum for small low conductivity gold) to 13us can make a big deal in "seeing" things. Where I hunt in desert, 90% of "junk" is lead pellets or bullets, so stuff like tin foil or pop-tops wouldn't pose a bigger problem.

Obviously I am not a detector engineer-just a rhetorical curiosity.

Anyone ever detect an area at say 10us, and then again at 13 or 15us to see the differences in detecting ability in the field or a test garden I wonder?

More than 50 years ago I was an electronics engineer before changing careers, and back then it would not have been easy to accomplish that (analog and digital microcircuits were pretty new then), but today it would likely be relatively easy. If changing delay slightly would catch more targets close to the nominal ideal delay (without finding mostly junk) it would be interesting (but beyond my obsolete capabilities, unfortunately).

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19 hours ago, Jim in Idaho said:

Yes...it's been known for a long time that you can use ML coils on TDI's, but  not the other way around.

Jim

Having been well behind the times by only recently purchasing a beautifully kept TDI, I did not discover that, though I did read (recently) posts where people just said they were "interchangeable," though it didn't mention it was one-way compatible until Miner John told me when he mentioned I should buy ML coils going forward rather than TDI coils as when I upgraded to an ML it would save me money and grief.

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7 hours ago, bobinyelm said:

Is it known what size/shape range it ignores? Or does it depend upon the coil used more than the machine itself?

Is it a function of the delay I wonder? It would be interesting if there were a way to "sweep" the delay, so that you could have it rapidly sweep +/-  20% above/below the selected delay setting. I've read that even the difference from 10us (the optimum for small low conductivity gold) to 13us can make a big deal in "seeing" things. Where I hunt in desert, 90% of "junk" is lead pellets or bullets, so stuff like tin foil or pop-tops wouldn't pose a bigger problem.

Obviously I am not a detector engineer-just a rhetorical curiosity.

Anyone ever detect an area at say 10us, and then again at 13 or 15us to see the differences in detecting ability in the field or a test garden I wonder?

More than 50 years ago I was an electronics engineer before changing careers, and back then it would not have been easy to accomplish that (analog and digital microcircuits were pretty new then), but today it would likely be relatively easy. If changing delay slightly would catch more targets close to the nominal ideal delay (without finding mostly junk) it would be interesting (but beyond my obsolete capabilities, unfortunately).

The problem can have many causes. Shape, porosity, alloys, etc. This problem is why ML's have so many adjustments, including variable timing. To find everything you may have to go over the same ground multiple times, with varied settings, but that beats leaving gold behind, though some will still not be indicated.

Jim

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On 3/22/2023 at 7:37 PM, Jim in Idaho said:

The problem can have many causes. Shape, porosity, alloys, etc. This problem is why ML's have so many adjustments, including variable timing. To find everything you may have to go over the same ground multiple times, with varied settings, but that beats leaving gold behind, though some will still not be indicated.

 

It would seem automatic variable timing/delay could be the easiest to incorporate (if that is a variable that improves more thorough detection), and would preclude multiple passes over the ground, so it makes me wonder why they have not done it.

Twisting a knob to select delay is kind of like having a knob like really old cars had on the top of the windshield to move the wiper blade. Now with microchips we have rain sensors that completely sense the rain, determine the intensity, select the speed of the wiper, and the speed/spacing of sweeps, and shuts off when the rain stops.

I mean the GPZ 7000 listed for $10,000 (now $8500 it seems). That's a LOT of money; for that price it should have wings and fly. I paid that for a PA18/150 Super Cub I had in Alaska not THAT long ago. You can practically buy/build a Super Computer for that kind of money https://www.asianscientist.com/2017/09/features/build-your-own-supercomputer-1000/ .

Software these days can work wonders.

The VLF Legend has multiple programs (There have been 11 software versions released, which are user downloadable, as user suggestions are adopted.) with virtually a huge list of user adjustable parameter, including multi simultaneous frequencies, or selectable single frequencies, all for $400 (machine with one coil or $600 with 2 coils, aux lithium battery, bluetooth headset and submersible to 10ft) , and it's not alone.

Most new VLFs are amazing, and I cannot believe that PIs couldn't benefit from this kind of magic.

Sorry for the rant, but I suspect that more is possible in PIs these days. Not enough competition, or large enough market.

I know there are detector designers/engineers that frequent the Forum. I'd love to hear their opinion on that.

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I am not an Axiom owner but am curious if Garrett's Axiom suffers from the same "blind spot" issue and if so  this poses a similar question as to how to fix it other than cover the same area with different settings?  Thanks

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10 minutes ago, Cascade Steven said:

I am not an Axiom owner,  but am curious if Garrett's Axiom suffers from the same "blind spot" issue and if so  this poses a similar question as to how to fix it other than cover the same area with different settings?  Thanks

I do not own or have ever tried an Axiom, but in a video test by "Chris Ralph, Professional Prospector" of an SDC2300 and the Axiom, both seemed comparable on small gold, but the Axiom was MUCH more affected by hot rocks than he SDC.

'Blind spot' was not addressed in his comparison:  (Note he also demonstrates the GM1000 VLF on mineralized soil and hot rocks, but it's the Axiom vs SDC2300 ($600 Cheaper than Axiom) that is operative if his test is representative and ability to ignore hot rocks is important to the user.) 

 

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2 hours ago, bobinyelm said:

...'Blind spot'...

Are you talking about "the hole" where certain gold nuggets don't sound off because of the ground balance point?  Steve H. has written about this a lot.  See this and this for starters.

2 hours ago, bobinyelm said:

...It's the Axiom vs SDC2300 ($600 Cheaper than Axiom) that is operative if [Chris Ralph's test shown on the linked video] is representative and ability to ignore hot rocks is important to the user.)

In the case of the Axiom, @Steve Herschbach likely has more experience than anyone, anywhere with the Garrett Axiom given he was a major tester of it months before it was even announced.  He's also written a lot about it here and produced videos for Garrett (available on YouTube), including how to eliminate hot rock signals.  I'm out-of-my comfort zone saying more than that, and I haven't watched the video, not that it would help since I'm ignorant at that level, not being interested in the Axiom due to rarely getting to nugget hunt.  But something doesn't sound right about the SDC2300 outperforming the Axiom unless it was for a very narrow choice of ground conditions, targets, etc.

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