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Frequency More About Target Size, Than Type Of Metal


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Makes perfect sense, I was told by my hunting buddies years ago when I got a shadow5 that I wouldn't dig any deep silver due to the troy freq. I believe it was 18-19khz? But I did, and on a regular basis.

But even Troy said it was geared more to relic hunters so that didn't help matters.

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Another non-intuitive target is the long-and-thin type. Such items include wire ( copper or brass, typically ), plain finger-rings that are broken ( C-shape ), copper/bronze/aluminium nails.

Metal detectors induce circulating electrical currents in the target that tend to form loops as large as they can, without straying too far from 'circular'. So for a wire, these current loops are little more than the wire diameter in size, they don't go up-and-down the length of the wire at all. There are many of these loops along the wire, so they all contribute to giving a stronger response to the detector, but the 'target frequency' is still that of a very short snippet of wire, no more than twice the diameter.
So wires tend to have very a high 'target frequency' , that's independant of their length. This can make them hard to detect.
An extreme example : among my electronics junk, I have some test coils that are much like the windings inside a detector search-coil. 100 turns of 0.2mm enamelled copper wire, over 20 grams of highly-conductive metal in total. But place one 5mm from a detector coil, it is invisible. The target freq is about 2.5 MHz, so it's not going to match any commercial machine.
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5 minutes ago, PimentoUK said:

So wires tend to have very a high 'target frequency' , that's independant of their length. This can make them hard to detect.

I find quite a bit of copper wire -- single stranded (but not coiled) used in constuction.  I think the gauge is in the 12-16 range.  They typically hit in the USA zinc penny and aluminum screw cap range.

IMO, an iron alloy nail oriented with its axis parallel the coil's axis (think vertical when in the ground) can give an interesting positive response.  Certainly the nail head contributes, but even nails without heads seem to show similar results.  My hypothesis is that what is effectively happening is similar to a stack of small discs which add constructively.  Do you have a different hypothesis for that apparent phenomenon (or am I just imagining this genearlization)?  Possibly I'm assigning a conductive explanation to a ferromagnetic property....

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14 hours ago, GB_Amateur said:

What I've never seen is a similar plot for copper-silver alloys.  You wouldn't happen to have that one?

Not a plot and a random source, but it seems that adding copper to silver lowers the conductivity of the alloy in similar fashion to gold-silver/copper alloys, below the conductivity of either pure metal.

fichesthesscopag2 (3).pdf

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15 hours ago, PimentoUK said:

Another non-intuitive target is the long-and-thin type. Such items include wire ( copper or brass, typically ), plain finger-rings that are broken ( C-shape ), copper/bronze/aluminium nails.

Metal detectors induce circulating electrical currents in the target that tend to form loops as large as they can, without straying too far from 'circular'. So for a wire, these current loops are little more than the wire diameter in size, they don't go up-and-down the length of the wire at all. There are many of these loops along the wire, so they all contribute to giving a stronger response to the detector, but the 'target frequency' is still that of a very short snippet of wire, no more than twice the diameter.
So wires tend to have very a high 'target frequency' , that's independant of their length. This can make them hard to detect.
An extreme example : among my electronics junk, I have some test coils that are much like the windings inside a detector search-coil. 100 turns of 0.2mm enamelled copper wire, over 20 grams of highly-conductive metal in total. But place one 5mm from a detector coil, it is invisible. The target freq is about 2.5 MHz, so it's not going to match any commercial machine.

OMG. Try nugget detecting in a location where bedrock has been cleaned with steel brushes! I have another location where a small shack had steel mosquito screens on the windows. Those have since decomposed and scattered across the placer due to high winds. The GPX 6000 is hot enough that these very thin 1/4" make a perfect small gold nugget signal. Hunting the area with a VLF and tuning them out miss the small gold. The only solution is a good magnet, as thankfully the targets are shallow. I've no solution though for the tiny lead birdshot I'm finding now with the 6000, that all my previous PI detectors missed.

This whole subject is about discrimination, and fact is for 90%+ of my detecting I use no discrimination. If a location has a high value target I want, there is for me no solution ultimately but to sanitize the location with the most powerful PI I can use. Discrimination is too unreliable, and masking is a massive issue. Yes, I dig tons of trash, but I also find lots of gold in locations others considered to be worked out. I'm talking ounces of gold, not a few nuggets. It is not just nugget hunters. Any beach, and relic location, where there are desired high value targets, all discriminating detectors are a just a phase, a waypoint. Once they start coming up dry, people will go to PI to finish up. Or move on to new locations. But no good site is truly done until something like a GPX 5000/GPX 6000/GPZ 7000 can simply find no signals. That's how you kill a gold patch - you hunt it until nothing goes beep. And that only lasts until a more powerful PI comes out. :smile:

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Interesting topic. I sent some targets to someone that has 6000 and 7000 detectors. Targets included #4, #6, #8 and #9 lead shot. Both detectors could detect #4 and #6 shot not #8 or #9 shot. Guessing coil size might be some of the reason. Is being able to detect #9 shot important, if so at what distance? 

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... the size of the coil is a very important factor, because it can sufficiently bend the basic detection properties of a certain frequency used ...

it's no secret ... the  small coil.... was able to significantly increase the sensitivity to very small-low-conductivity objects ... even at the low detector frequency used ...


But the coil size factor ... it also works in the opposite direction ... for example, with a detrector operating at 19-30 khz and more, a large 11 "or 13" coil can significantly improve detection, especially on higher conductors.

 the detector's sensitivity to very small things affects 3 essential things ...

1. Detector power - a powerful detector even at our used frequency is still sensitive enough to very small things ...

2. the size of the detector frequency used ... the higher the frequency, the higher the sensitivity to small things.

3 .. coil size ... optimally the coil was able to significantly improve the sensitivity and reach of the detector on very small things ..

Sufficiently powerful and sensitive detector working at 6.6khz on a standard 11 "coil was able to detect 3 times in a row on a 2m section of a lighty snowed forest road .. small  4.5 mm lead shot ..don't be surprised because the airest of 0.1gram of gold is somewhere at 11.5cm...

no it wasn't a coincidence, because in various detections I dug for 1 search for example 2 shots with a detector working at 6.6khz ,,,

but again I have to admit that with detectors operating on 19khz and 11 "coils/Tek G2/, the average was, for example, 3 shots for a similarly short search ..

the higher frequency definitely improves the chances of better detection of very small things ..but the detector must also be powerful enough...

5aa26a04ba5f8_sonysola1073(600x337).jpg.2545ac4d336b5a76c5fd58dcbda69d84.jpg

.....however, it is clear that there is a certain target size limit where there will be a better high frequency detector, for example, working at 48 khz ...

 

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On 1/21/2022 at 1:07 PM, Chase Goldman said:

infamous cloud diagram

😂😂😂😂

Actually I found an interesting middle range among two clouds and Steve's words...🙏

We'll see the next week if I'm wrong...Or not💣

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