Understanding difference between low and high frequency

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GeoffBristol
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Understanding difference between low and high frequency

Post by GeoffBristol » Wed Dec 21, 2011 5:50 pm

Hi, This maybe a question for,Fusion or one of the other electronics experts on the forum,we all talk about frequency and myself for one just take it for granted, but I would like to understand it more, not being technically minded I would appreciate it if some one could explain it all to me,the question is, I believe that a lower say 8khz punches deeper into the ground than 18khz ,(depending on soil conditions) if this is correct is it possible to show me on a graph how and why it works,I hope I am not asking to much.
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Barnet
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Re: Understanding difference between low and high frequency

Post by Barnet » Wed Dec 21, 2011 6:01 pm

Higher frequencies have a shorter wavelength/closer together which can be more sensitive to smaller and lower conductive. Higher frequencies don't have as good of ground penetration in mineralized ground as lower frequencies.

Lower frequencies have a longer wavelength/further apart which makes it more sensitive to higher conductive targets. Lower frequencies tend to do better in mineralized ground, but are not as sensitive to small targets.

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Fusion
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Re: Understanding difference between low and high frequency

Post by Fusion » Wed Dec 21, 2011 6:37 pm

The maximum depth at which you can detect a target is limited by your detectors ability to distinguish between the ground signal and the target signal.
The ground signal is mainly caused by tiny bits of iron/rust, whose size is such that your detector would need to operate at MegaHertz to pick them up well. But the higher the frequency your machine operates at, the better it gets at responding to the ground, and the harder it becomes to seperate target from ground.
But.... targets have a 'best frequency' for detecting them at. Milled silver/copper/bronze coins, for example would be easiest to find with a 5 KHz machine. Cupro-nickel coins, ringpulls, ladies gold rings would be easier at 20 KHz. Tenth-gram gold nuggets would be best hunted with a 50 - 100 KHz detector. (it's not to do with the wavelength of the detectors signal - that is about 20 miles, not coin-sized).
Take a look on Minelab's website, there are a couple of good technical PDF's explaining detector operation.
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Re: Understanding difference between low and high frequency

Post by GeoffBristol » Wed Dec 21, 2011 7:43 pm

Thank's Barnet,and Fusion, I understand all that you have said and it seems that the thing to do is find out how minerialised the ground is and find a happy medium with the khz's setting,and adjust the sensitivity to suite,is this correct, I have had a look at the minelab site it's going to take me awhile to digest it all.
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Re: Understanding difference between low and high frequency

Post by Phil-field » Thu Dec 22, 2011 12:09 pm

What a great question Geoff,
One Ive thought of asking myself.
Brilliant easy to understand replies too from Barnet / Fusion Thanks lads, every little helps. =D>

Phil.

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Re: Understanding difference between low and high frequency

Post by woody50 » Sun Jan 08, 2012 7:24 am

Very good answers, and correct too Fusion and Geoff. I could not have answered better. A few years ago I searched a number of times in Serbia, searching high in the mountains between all the trees (first had to climb most of the time for about 1-2 hours).

Anyway I used a GMP and other detectors, sensitivy as high as it could go, 0 discrimination, all metal (relic). Searching for mostly iron, and had some very good finds. Even at those settings the detector was quiet most of the time, so I had to use my shovel to see if it was still working. No one was there (besides detectorists) for centuries, so NO junk.

The areas where we searched were old Byzantine forts, which were destroyed by the Turks after they took over the area. Everying was pushed over the sides of the mountains, so there were the finds; difficulty in searching? YES. And that is not including the pointed barbs on the trees and plants, and all the tree ROOTS, and sliding down the sides (some were too steep to hunt).... but fun.

Because I was searching for only really iron artifacts I used as low of a frequency as possible, to go deep. So I would agree with the answers and think about what you want to find. If your want only iron, set you detector for that, if you want only no-iron, set your detector for that. But use your ears first, meter second.. I usually go over a field with a High Frequency and later (if there were good finds) go again over the field with the lowest frequency that the detector can use.
Deus user, located in Zwaag, The Netherlands. Our tiny MD Club is called the WF4 (West Friesiae 4) http://www.wf4.nl

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Re: Understanding difference between low and high frequency

Post by stejens » Sun Jul 10, 2016 1:38 am

So how does this work with depth, like a low frequency punches deep into the ground and misses small signals like little hammies on the way down to it's max depth?, and low frequency goes down a couple of inches but picks up all the little targets?.
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