metal detector frequency and how it affects finds ?

[dfmike]

I'd like to know more about detector frequency and how it affects what can be found with the detector (size of targets, conductivity of targets, depth, etc.). Any forum posts or external links would be appreciated. Thanks.

 

[BillF]

Certain frequencies are supposed to be partial to certain metals. They very well may be. I personally believe that no matter the frequency if your coil is over it you're going to pick it up. However, the different frequencies might have more of a positive effect on certain soils and soil conditions.
If you're at all concerned with it, get a multi freq detector.

 

[bootyhoundpa]

General theory is high frequency is better at finding low conductors such as lead and gold... low frequently is better at finding high conductors such as copper and silver... i would be more concerned with target separation than frequency. .. i have found more gold with my whites 6.59 frequency 5900di pro than any of my other detectors. .. when it comes to saltwater multi frequency is necessary for best results...

 

[REVIER]

I never careed about this at all being an all around hunter.
I have found way more than my share of gold with an under 6kHz unit and silver with higher 14kHz units.
If I specialized in any area, gold nugget hunting or only combing old sites for the deepest silver I would think differently but I have found more than I ever thought possible at a decent range of depths in both good and bad soil under many conditions with all of them so for me a non issue.
Nice to have a choice, though, and I see more multi frequency units seem to be coming on board now without needing to switch coils like the soon to come Nokta Impact with it appears to be selectable choices of 5,14 or 20kHz and who knows...maybe a new Fisher that might do this soon to come or others.
Might be the wave of the future.

 

[Mike Hillis]

That is kind of a mini book request, Mike.

I'd suggest reading the DFX operating manual and the V3i Advanced book.

Frequency affects phase response and phase response affects both ground cancelling and target discrimination.

I have too much in my head to put it out in a simple manner. But the reading I suggested will help start you in the right direction.

HH
Mike

 

[still looking 52]

dfmike, the two main reasons I like the f5 multi frequency is to cut out EMI and also when hunting with other machines around close to you, you can cut down on detector interference. Personally I don't think it affects what you find that much at all.

 

[dfmike]

That is kind of a mini book request, Mike.

I'd suggest reading the DFX operating manual and the V3i Advanced book.

Frequency affects phase response and phase response affects both ground cancelling and target discrimination.

I have too much in my head to put it out in a simple manner. But the reading I suggested will help start you in the right direction.

HH
Mike

Thanks Mike I will try to find those manuals. They should be available online I suppose. I was indeed looking for a scientific explanation possibly from a designer, engineer perspective. I know the very basic theory that some have pointed out here but I'd like to know more.

Thanks to all for the information.

 

[dfmike]

dfmike, the two main reasons I like the f5 multi frequency is to cut out EMI and also when hunting with other machines around close to you, you can cut down on detector interference. Personally I don't think it affects what you find that much at all.

I use that a lot on the F5 to cut down on EMI at times. What I meant by my original post was more about the differences between detector main frequency like 5.9, 7.8, 13, 19 kHz and higher.

 

[amberjack]

M&M's
op's did I say that out loud I cant stop eating them

really I think its about ground and how the detector see's it and the metal humans have left behind, this non seeing or missing items has a lot to do with the detector not seeing the human item that's why there always seems to more stuff left granted it gets less but ground cancelling and then seeing the human left behind metal maybe more of an issue than we as laymen may really ever know.

this is a good and not so good thing good cause no one gets it all and we get to go back and hunt some more not so good cause we really don't know what we didn't find??

as for op freq low freq deeper higher not so much, and the standard high low conductor thing we always hear about, like the Gold Racer it does hit hard on low conductors and isn't very deep.

but as the saying goes what ever works and time behind the wheel etc....

its why its fun I guess no one has all the answers

AJ

 

[Jim in Idaho]

Higher frequencies induce a higher current in the metal, regardless of the type of metal. Unfortunately, you get less ground penetration at higher frequencies, so there's a tradeoff. When you talk about "low" conductors and "high" conductors is actually the strength of the magnetic field induced in the target by the detector. Gold is a very good electrical conductor, but doesn't produce as strong a field as iron. The way a detector works is the transmit coil's magnetic field penetrates the ground and induces a current in the target. That current in the target generates it's own magnetic field, which induces a current in the detector's receive coil. Since the magnetic field produced in an iron target is much stronger for a given current, iron is much easier for the detector to "see". One of the determining factors for the strength of the magnetic field is the frequency of the signal induced in the target....thus high freq's induce a stronger field. But, that higher freq also induces stronger fields in the ground minerals, too. One of the best detectors ever made for finding tiny gold nuggets is the Fisher GBII.....it operates at 73khz.....way up there for a detector. But, it doesn't go very deep.....that high freq causes the ground minerals to block the penetration of its transmitted field, so it is great on near-surface tiny targets, but not so good at deeper stuff. The reason the ground minerals are a problem is that magnetic fields tend to resist each other. The fields produced by the minerals are random.....mostly they resist the field of the detector, thus limiting depth. Fortunately, they are much weaker than the target returns. So, generally the lower freqs have more penetration, while higher freqs will find smaller targets. You can't make absolute claims on which is better, because the amount, and type, and size of ground minerals have a big impact on what happens. Every locale is different, and the best detector in one place may not be worth squat in another.
Jim

 

[Nauti]

The best two detectors ive ever owned both ran at 14khz.These detectors have found me many tiny hammered and roman coins over here in England.......both American made by the way.

 

[dfmike]

Thanks Jim. Your explanations pretty much echo what I've experienced in the field with 2 different frequency detectors (7.8 and 19 kHz). Although I wouldn't say that the difference in depth is easily noticeable between both (at least so far where I've been hunting). Of course there's a lot more to a detector than frequency alone, it helps me understand what is going on and why I'm finding smaller and more stuff in the foil, pull tab and nickel range with the high frequency detector.

 

[hairymonsterman]

I run a 2 freq machine, the difference in the air test pics are pretty much how it plays out in the ground with this 10"x12" coil.
8khz top pic, but 18khz always gives a stronger audio.
18khz bottom pic.
On coins my 5" coil works best in 8khz, 9" coil is pretty much equal in both freq, 15"x12" works best in 8khz.
My ground is med/high, results will vary in different ground.