frequency 101

How does frequency work in regards to finding targets? thanks

example why is a certain frequency good on gold nuggets or tiny targets??does the ground minerals effect frequency??

Hi,,,,Detectors properly built for gold etc. are built to be close to the objects/elements resonant frequency that it was designed for....Supposedly all elements on earth have/emit what is called a natural frequency......Higher frequency machines can see smaller items because the waveform is smaller than a lower frequency machine....A 18kHz machine is sending out 18000 cycles per second Vs a 7kHz machine at 7000 cycles per second plus that fact that there's more waves doing the analyzing of a target ....Here's examples of what I talked about above to draw a clearer picture.. ...Resonant frequency::::A person breaking a wine glass with their voice when it hits the resonant frequency of the wine glass....Higher frequency machines seeing smaller items:::: A smaller higher frequency satellite dish & receiver (dish network etc.) will/can see rain drops that's why the picture will sometimes go out during a big rain storm....On the other hand the lower frequency older C-band satellite dish & receiver can not see a rain drop and is not bothered one bit by a big rainstorm....And lastly you asked "do ground minerals effect frequency"....No they don't affect or alter the frequency they do however limit the depth of a metal detector....A lower frequency machine should offer more depth over a higher frequency machine....JJ


PS: Hey if this is not correct it sure sounds good huh?....LoL

jimmyjiver Wrote:
-------------------------------------------------------
> Hi,,,,Detectors properly built for gold etc. are
> built to be close to the objects/elements resonant
> frequency that it was designed for....Supposedly
> all elements on earth have/emit what is called a
> natural frequency......Higher frequency machines
> can see smaller items because the waveform is
> smaller than a lower frequency machine....A 18kHz
> machine is sending out 18000 cycles per second Vs
> a 7kHz machine at 7000 cycles per second plus that
> fact that there's more waves doing the analyzing
> of a target ....Here's examples of what I talked
> about above to draw a clearer picture..
> ...Resonant frequency::::A person breaking a wine
> glass with their voice when it hits the resonant
> frequency of the wine glass....Higher frequency
> machines seeing smaller items:::: A smaller higher
> frequency satellite dish & receiver (dish network
> etc.) will/can see rain drops that's why the
> picture will sometimes go out during a big rain
> storm....On the other hand the lower frequency
> older C-band satellite dish & receiver can not see
> a rain drop and is not bothered one bit by a big
> rainstorm....And lastly you asked "do ground
> minerals effect frequency"....No they don't affect
> or alter the frequency they do however limit the
> depth of a metal detector....A lower frequency
> machine should offer more depth over a higher
> frequency machine....JJ
>
>
> PS: Hey if this is not correct it sure sounds good
> huh?....LoL


Very interesting thanks.

Quote:"Hey if this is not correct it sure sounds good"
The general idea of JJ's reply is correct. The flaw is the idea that targets are 'tuned'. They're actually very 'un-tuned', which is good, as we would all need multiple-frequency Deus-like machines to find anything. But targets do have a response that varies with frequency. There is a measureable characteristic, the "corner frequency" ( -3dB frequency / break frequency). A detector operating in this general frequency range or higher would work best. What doesn't work so well is a detector frequency much lower than the target. The target becomes harder to distinguish from the ground's "iron" signal.
Nuggets, tiny targets can have 'corner frequencies' in the 20 - 100 KHz range, which is why nugget-hunting machines have those kind of operating frequencies.
And, as JJ said, the ground gives a stronger response at higher frequencies, which ultimately leads to depth loss.

Hi,,,I figured someone would dispute what I wrote..LoL...I just tried to keep the answer simple and explained it in layman's terms....Of course there is a ton of variables in the equation....Why cloud someones mind with an overindulgence of facts and theories that only serves to confuse them more.....The premise is the same while keeping the answer simple for all to understand....If a coin etc. always resonated properly at depth a machine would properly ID correctly all the time....We all know this don't happen all the time, so the quest continues....Let's not forget harmonics & sub harmonics etc......Just remember You Can Tune a Piano, but You Can't Tuna Fish....LoL....JJ

Thanks for the general idea, now if targets have their own tuning frequency then is this frequency in pulltabs,nickels,gold very close? If not then why do they read the same often?? ok read againthe above post.



Edited 1 time(s). Last edit at 05/31/2015 03:45PM by guvmore.

Hi,,,An air test of objects would give you a Perfect World deviation/variance of the ID numbers an object displays... But when you add moisture,dirt/mineralization,co-located objects etc. to the equation the detectors will sum up what is being seen by/under the coil at any given time....The machine can only report/ID the combination of all these variables, density/mass of an object affects the outcome also....Once in awhile you will get a perfect text book ID of an object in the ground and this usually happens when the object/coin is isolated mainly by itself.....Keep in mind that some machines have better ID capabilities than others..... JJ

jimmyjiver Wrote:
-------------------------------------------------------
> Hi,,,An air test of objects would give you a
> Perfect World deviation/variance of the ID numbers
> an object displays... But when you add
> moisture,dirt/mineralization,co-located objects
> etc. to the equation the detectors will sum up
> what is being seen by/under the coil at any given
> time....The machine can only report/ID the
> combination of all these variables, density/mass
> of an object affects the outcome also....Once in
> awhile you will get a perfect text book ID of an
> object in the ground and this usually happens when
> the object/coin is isolated mainly by
> itself.....Keep in mind that some machines have, jj


ok, seems logical now, anyway we don't want detecting to be too easy



Edited 1 time(s). Last edit at 05/31/2015 04:20PM by guvmore.

Easy, Jimmy, your reply was just as techy as mine, it's kind of hard to answer a technical question without giving a technical answer. Plus, there are other readers out there who probably do like some tech with their detecting.

And nickels, pulltabs, read close because their corner frequencies are close. Though it's worth pointing out that target ID values (the 00 - 99 reading) are contrived, they're squashed and stretched as the designer sees fit. So in principle you could have a 'nickel' mode on a machine, where that small range around nickels/pulltabs filled the entire 00 - 99 range. I can't see it being all that helpful, though, myself.

Hi,,,,There's actually a lot more information to add to the above answer but I certainly don't want to get into it all....Orientation & proximity of an object/coin to the surface will also skew ID numbers somewhat.....But I think you now have enough basic information to satisfy your need to succeed.....JJ

Metal targets have a frequency response, but they don't have a "resonant frequency" per the popular notion of Brunhilde shattering a goblet. Nor does "everything in nature" have such a resonant frequency, this is the balderdash realm of long range locator enthusiasts.

Target response depends on metal composition, size, and thickness; and, of course, orientation and depth, plus composition of the matrix. Assuming the matrix is air and we have a flat-oriented target close enough to give a nice strong response, of the first 3 characteristics it is thickness that matters the most.

Non-ferrous targets are detected via induced eddy currents, and the effect of "skin depth" plays a crucial role in the phase response (TID) of the target. Skin depth depends on metal conductivity and frequency, and the short of it is that identical metals with different thicknesses will have different TIDs for a given frequency. You can see this with a silver dime and a silver dollar, both have the exact same alloy.

Higher frequencies result in shallower skin depths, which for thin targets produce a better response. Lower frequencies result in deeper skin depths, which help with thick targets. In addition, low frequencies work better in high mineralization and wet salt. Also, low frequencies tend to expand the high range of TIDs and compress the low range, while high frequencies do the opposite. Therefore, low conductors are not only harder to detect with a low-frequency detector due to skin depth, they are more difficult to distinguish from one another because the low end is compressed and TIDs are close together. Although a designer could artificially expand this back out, the reality is that the TIDs would simply jump all over the place.

Hi Pimento,,,I hear ya on the ID span that's why I said...."Keep in mind that some machines have better ID capabilities than others".....I kinda laugh and don't answer a lot of stuff because it usually gets debated,challenged or ignored....On the other hand I don't want to come off as a know it all neither but sometimes I feel somewhat obligated to reply ....I do see some wrong advise given here or there or at least in my books it's wrong but I try to stay/remain neutral....I only replied to his post because it went unanswered for so long,so I said to myself what to heck I will take a stab at it....LoL...Even after four decades I'm still in the learning phase but I do have a thirst/weakness for knowledge....Best of luck to you.....JJ

Carl......... nice/technical/educational/professional disseminated data. Thanks for taking the time.

I WILL JUST DIG EVERYTHING

Pimento Wrote:
-------------------------------------------------------
> Easy, Jimmy, your reply was just as techy as mine,
> it's kind of hard to answer a technical question
> without giving a technical answer. Plus, there are
> other readers out there who probably do like some
> tech with their detecting.
>
> And nickels, pulltabs, read close because their
> corner frequencies are close. Though it's worth
> pointing out that target ID values (the 00 - 99
> reading) are contrived, they're squashed and
> stretched as the designer sees fit. So in
> principle you could have a 'nickel' mode on a
> machine, where that small range around
> nickels/pulltabs filled the entire 00 - 99 range.
> I can't see it being all that helpful, though,
> myself.



To be honest I always did think the ID values were somewhat contrived and more of design fluff, is there any truth that rain may give extra depth? it does seem I do my best find totals after the rain? HH THANKS for taking time to clear up a few questions.

Generally a higher freq likes lower conductors..

A lower freq Likes Higher conductors...

This also holds true to targets sizes...usually a higher freq will see larger targets at depth and higher freq can see smaller targets at depth compared to each other...

Since we like to look for coins and button's and such manufacturers usually dont push much past 20Khz on the High range unless they are building a Micro Gold machine...

On the low end the usually like ot get freq around 7 or 8 Khz for affinity to coin's of high conductance at depth ,,,

Now things dont always hold true to freqs and alot of manufacturers like to get in the middle of the road so to speak...and shoot for around 13Khz sort of make the machine more even on higher and lower conductors...And nowadays manufacturers have figured out ways through processing and coil design to UPSET some current thoughts..especially with what they can do in the Mid freq ranges...


To puch mineral a DD works better usually than a Concentric of same size...at a cost of some depth on the extreme depth end but not much,,,only noticable in GOOD dirt usually...


High freqs seem to allow for faster recovery or adjacent targets seperation..and youll notice msot of your brst iron unmaskers use a freq of say 15-20 khz...and have a tight DD coil and an affintiy for smaller targets...

this is just minimal info .and maybe it will help..

Keith

“I don't care that they stole my idea . . I care that they don't have any of their own”
-Nikola Tesla

It's not 'design fluff'. The engineers choose the scaling with care, allowing for the intended use of the machine, and technical factors related to precision, ease of use by the customer. Take the Tek T2 and the Fisher F75. They're the same basic machine, the microprocessor brains has the same info available to it. But the F75 was designed to be more useful to coin-hunters. So while the T2 has a non-iron range of 59 points (40 -99), the F75 has 85 points, opening up the spread, allowing you to distinguish targets like zinc-cored cents from copper ones from dimes etc. It could have been designed to have iron read 00 -> 09 even. Or -9 -> 0, or they might have decided to use a 188 readout on the LCD, and really spread out the ID's.
I only used the word "contrived" because the displayed number bears no obvious relationship to any real physical characteristic of the target, like its phase lag, or corner frequency. Similarly, machines that give ground-balance phase readouts are not giving you actual hard-to-fathom data, but tinkered-with numbers that make easier reading and fit an '88' display.

There are several threads on here about wet ground, the search function should find them.

I really like my 18 kHz machines for park hunting, especially because they like our older nickel coins.
Further they won't dig too deep and are my favourite on a first pass in the park.

My mid frequency 13kHz machine is a real depth monster and seems to like everything. Wouldn't want to be without it.

Didn't get along with 3kHz machines, too much EMI and we don't have much large silver coins.

Great read from Geotech,... explaining to us "users of the magic" the principle of Skindepth.

HH
Johnb

Hi,,,,Yeah it's always great to hear Carl's insights on a particular subject....I guess I need to un-resonate my resonator and discombobulate my frequencies....LoL...On Myth Busters a few years ago they was making objects resonate and actually did break wine glasses etc...it was a good show.... What's your frequency Kenneth?......JJ