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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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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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>

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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.
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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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Re: Understanding difference between low and high frequency

Post by Twit » Sat Dec 30, 2017 3:53 am

Woody50 that sounds like my kind of detecting , I detest finding loads of trash and am happy with no signal unless good signal.. some places I have been are one signal every ten minutes, so even if no good they make a change. I also use 18kHz and it suits me fine , on my machine it gives a very fast response and good separation. There are some trench test videos showing 18khz making very good depth on medium soil even for high conductors . You do notice the soil effect... when I go on clean non salt sand it boosts performance. The only thing I haven't figured yet is coil size and depth... a bigger coil should get more depth, but this can be offset by increased reception of ground signal on poor soil.... not sure but in salt water seems much clearer and deeper with a small coil. Mean to ask littleboot if she bought the nel thunder coil for her high freq. and how that worked if so ... just nothing clear on the web for that coil and high freq.

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Re: Understanding difference between low and high frequency

Post by fred » Sat Dec 30, 2017 5:01 am

Some great answers which probably also goes some way towards explaining the logic behind multifrequency detectors. ::g

With programmable detectors I always start my detector setups on the assumption that maximum depth and sensitivity comes from having all the controls set so that they affect the detector least. Depending upon function this may be maximum or minimum. These setting might then have to be changed to make the detector more stable in real use or to add in personal preferences. However, every change should be made cautiously because it compromises depth or sensitivity.

In my fields if I am finding small bits of nonferrous at serious depth and digging about 10% iron then I have the detector set about right. The proportion of iron may even be a bit higher on beaches because good targets are often very deep and I am trying to squeeze out extra depth by digging some very marginal signals.

Probably simplistic from a technical perspective but it works OK for me! :D
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Re: Understanding difference between low and high frequency

Post by Wilci » Sat Dec 30, 2017 9:23 am

Twit wrote:
Sat Dec 30, 2017 3:53 am
Mean to ask littleboot if she bought the nel thunder coil for her high freq. and how that worked if so ... just nothing clear on the web for that coil and high freq.
I'm puzzling with the same question. Looking in particularly for small targets as halve hammies, sceat's and minimissimi. (0,5 - 1 grams)

Will, for example, the Equinox goes deeper in 40Khz with the 11"coil on these targets than my Deus with the HF 9"coil in 28 or 74 Khz?
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Re: Understanding difference between low and high frequency

Post by fred » Sat Dec 30, 2017 10:35 am

Wilci wrote:
Sat Dec 30, 2017 9:23 am
Twit wrote:
Sat Dec 30, 2017 3:53 am
Mean to ask littleboot if she bought the nel thunder coil for her high freq. and how that worked if so ... just nothing clear on the web for that coil and high freq.
I'm puzzling with the same question. Looking in particularly for small targets as halve hammies, sceat's and minimissimi. (0,5 - 1 grams)

Will, for example, the Equinox goes deeper in 40Khz with the 11"coil on these targets than my Deus with the HF 9"coil in 28 or 74 Khz?
Unfortunately I rather suspect that the answer will be that it depends upon where you are detecting and how you use it. :D
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Re: Understanding difference between low and high frequency

Post by oldartefact » Sat Dec 30, 2017 11:35 am

What I would like to know is how different frequencies work on the same ground for the same size target.
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Re: Understanding difference between low and high frequency

Post by Twit » Sat Dec 30, 2017 3:49 pm

fred wrote:
Sat Dec 30, 2017 10:35 am
Wilci wrote:
Sat Dec 30, 2017 9:23 am
Twit wrote:
Sat Dec 30, 2017 3:53 am
Mean to ask littleboot if she bought the nel thunder coil for her high freq. and how that worked if so ... just nothing clear on the web for that coil and high freq.
I'm puzzling with the same question. Looking in particularly for small targets as halve hammies, sceat's and minimissimi. (0,5 - 1 grams)

Will, for example, the Equinox goes deeper in 40Khz with the 11"coil on these targets than my Deus with the HF 9"coil in 28 or 74 Khz?
Unfortunately I rather suspect that the answer will be that it depends upon where you are detecting and how you use it. :D
I think that is very much the case, only a side by side real life comparison in different conditions with different settings will give a proper answer. If I had different machines to compare I would set up a serious testbed and record results right down to swing speed etc. The hobby is missing this kind of comparative analysis.

Oldartefact - at a practical level ( because I imagine what goes on between a signal emitted, how interacts with soil and target, and how it is then processed, is beyond proper scrutiny) all there is are real life tests. In theory lower frequency will penetrate deeper and ring out high conductors clearer... in theory . I have found only that the signal on low frequency is clearer in volume, not really depth or other detail... just a completely unscientific answer from the few machines I have tried.

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Re: Understanding difference between low and high frequency

Post by oldartefact » Sat Dec 30, 2017 4:45 pm

Twit wrote:
Sat Dec 30, 2017 3:49 pm
fred wrote:
Sat Dec 30, 2017 10:35 am
Wilci wrote:
Sat Dec 30, 2017 9:23 am


I'm puzzling with the same question. Looking in particularly for small targets as halve hammies, sceat's and minimissimi. (0,5 - 1 grams)

Will, for example, the Equinox goes deeper in 40Khz with the 11"coil on these targets than my Deus with the HF 9"coil in 28 or 74 Khz?
Unfortunately I rather suspect that the answer will be that it depends upon where you are detecting and how you use it. :D
I think that is very much the case, only a side by side real life comparison in different conditions with different settings will give a proper answer. If I had different machines to compare I would set up a serious testbed and record results right down to swing speed etc. The hobby is missing this kind of comparative analysis.

Oldartefact - at a practical level ( because I imagine what goes on between a signal emitted, how interacts with soil and target, and how it is then processed, is beyond proper scrutiny) all there is are real life tests. In theory lower frequency will penetrate deeper and ring out high conductors clearer... in theory . I have found only that the signal on low frequency is clearer in volume, not really depth or other detail... just a completely unscientific answer from the few machines I have tried.
Twit, are you trying to say. in usual eloquent style, that the industry is plagued with smoke and mirrors ,,, in some desperate attempt to outwit and outsell competitor suppliers... there is no gold standard, so we dont really know what we are getting when buying a detector,
I would hope that there is a very simple answer to my question ... same ground, same target, how do different frequencies respond ... something like ... low frequencies are more precise for small deep targets and high frequencies are more precise for larger shallower targets... but what often happens is that we get a mix of information... small target, mineralised, at depth = high frequency, and large target, unmineralised, shallow = low frequency ... and as my brain only works in 2-dimensions (at best) I'm left out in the cold.
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Re: Understanding difference between low and high frequency

Post by Twit » Sat Dec 30, 2017 5:15 pm

In short.

Then again there is no perfect ideal applicable to any particular individual, just a mix of attributes to each detector that somehow fit together well with any person's style and demands. Even the gold standard required a certain amount of hypothecation, as in credit and promisary notes did act as a form of money ( with discount) ... the difference being as compared with fiat ( credit in perpetuity) that there existed a point of reconciliation when accounts went bad , meaning only someone got the gold. That is self limiting and invites prudence, as opposed to " let's take rates negative, we need more horses". Even the previous EMU failed simply because of lack of respect by certain governments.

All depends on perspective.

[Edit in ... to me lf are more precise/obvious for high conductor deep, hf are more precise/obvious for medium/shallow small targets, more obvious for lower conductors such as gold. On a broader note, a sensible starter machine will find well over half of what a higher end machine will find, irrespective of frequency, including some of the best finds. Hf is good for gold, small fragments, overall discrimination and in trashy ground, usually has faster clearer timing = better definition which suits very active detecting also. For salt water, dual frequency or pi make a looot of difference. For gold, particularly smaller gold, hf or pi make looots of difference. For outright depth without easy disc, pi and top end machines win. ]
Last edited by Twit on Sat Dec 30, 2017 6:10 pm, edited 1 time in total.

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Re: Understanding difference between low and high frequency

Post by sweepstick47 » Sat Dec 30, 2017 6:01 pm

oldartefact wrote:
Sat Dec 30, 2017 4:45 pm
Twit wrote:
Sat Dec 30, 2017 3:49 pm
fred wrote:
Sat Dec 30, 2017 10:35 am


Unfortunately I rather suspect that the answer will be that it depends upon where you are detecting and how you use it. :D
I think that is very much the case, only a side by side real life comparison in different conditions with different settings will give a proper answer. If I had different machines to compare I would set up a serious testbed and record results right down to swing speed etc. The hobby is missing this kind of comparative analysis.

Oldartefact - at a practical level ( because I imagine what goes on between a signal emitted, how interacts with soil and target, and how it is then processed, is beyond proper scrutiny) all there is are real life tests. In theory lower frequency will penetrate deeper and ring out high conductors clearer... in theory . I have found only that the signal on low frequency is clearer in volume, not really depth or other detail... just a completely unscientific answer from the few machines I have tried.
Twit, are you trying to say. in usual eloquent style, that the industry is plagued with smoke and mirrors ,,, in some desperate attempt to outwit and outsell competitor suppliers... there is no gold standard, so we dont really know what we are getting when buying a detector,
I would hope that there is a very simple answer to my question ... same ground, same target, how do different frequencies respond ... something like ... low frequencies are more precise for small deep targets and high frequencies are more precise for larger shallower targets... but what often happens is that we get a mix of information... small target, mineralised, at depth = high frequency, and large target, unmineralised, shallow = low frequency ... and as my brain only works in 2-dimensions (at best) I'm left out in the cold.


Hello John ::g Can't help with the first (technical bit) so I'm just going to recommend a 'Hot Toddie' to satisfy the latter statement :D Have a Great New Year -=+:-P Cheers Eric
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Re: Understanding difference between low and high frequency

Post by oldartefact » Sat Dec 30, 2017 6:08 pm

sweepstick47 wrote:
Sat Dec 30, 2017 6:01 pm
oldartefact wrote:
Sat Dec 30, 2017 4:45 pm
Twit wrote:
Sat Dec 30, 2017 3:49 pm


I think that is very much the case, only a side by side real life comparison in different conditions with different settings will give a proper answer. If I had different machines to compare I would set up a serious testbed and record results right down to swing speed etc. The hobby is missing this kind of comparative analysis.

Oldartefact - at a practical level ( because I imagine what goes on between a signal emitted, how interacts with soil and target, and how it is then processed, is beyond proper scrutiny) all there is are real life tests. In theory lower frequency will penetrate deeper and ring out high conductors clearer... in theory . I have found only that the signal on low frequency is clearer in volume, not really depth or other detail... just a completely unscientific answer from the few machines I have tried.
Twit, are you trying to say. in usual eloquent style, that the industry is plagued with smoke and mirrors ,,, in some desperate attempt to outwit and outsell competitor suppliers... there is no gold standard, so we dont really know what we are getting when buying a detector,
I would hope that there is a very simple answer to my question ... same ground, same target, how do different frequencies respond ... something like ... low frequencies are more precise for small deep targets and high frequencies are more precise for larger shallower targets... but what often happens is that we get a mix of information... small target, mineralised, at depth = high frequency, and large target, unmineralised, shallow = low frequency ... and as my brain only works in 2-dimensions (at best) I'm left out in the cold.


Hello John ::g Can't help with the first (technical bit) so I'm just going to recommend a 'Hot Toddie' to satisfy the latter statement :D Have a Great New Year -=+:-P Cheers Eric
Think that it will have to be at least 3, and many thanks for your wit and wisdom!! Its very much appreciated in these dark times :) :) :) All the very best for the new year.
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