Frequencies ????

[gmanlight]

This is not a mod but you guys know your stuff so i went here

I hear people and have read low frequencies go deeper but yet other than ML

F75 14Kz Tejon 17 Kz Troy 17 Kz and other deep seekers run on the hi side

So whats the deal does it even matter i was just curious thanks Mike

 

[Southwind]

I think lower frequencies penetrate mineralized soil better than higher frequencies, and higher frequencies are more sensitive to small low conductive targets. A happy medium would be in the 9-17khz range. I think where you would see a big difference in lower frequency depth would be in highly mineralized soil, on a high conductive target.

When hunting tot lots and beaches I use 15khz and when hunting deep coins I use 3khz on my DFX.

 

[UK Brian]

That was the situation, especially with the pre motion machines but they can now design high frequency machines that go deep.There's a bit on this on the Dave Johnson interview that went on the web after the T2 came out.
There's dozens of detectors both U.S. and European that are low frequency. 1 kHz, 4 kHz and the Whites and old Bounty Hunter favourite frequency of 6.592 kHz.

 

[GoGoGopher]

To my knowledge, frequency has little to do with depth...The strength of the signal penetrating the ground has to do with Depth also the tuning and how good the receiver in the machine is...Frequency has more to do with the type of metals the machine will respond to best...Southwind had the right idea....low frequency for deep coins and relics...higher frequencies for small gold and rings...


HH,

GoGoGopher

 

[UK Brian]

Sorry fiction, not fact.
This is the results of in ground tests. Not "I once read" or "I think"

At any frequency the most important factor is the surface area directly parallel to the bottom surface of the coil.
Lower frequencies have the capabability of adding to the surface area signal if the metal item is thicker but limited to approx. one quarter of an inch. Beyond that thickness there is no more penetration into the item.
High frequencies have markedly less penetration but can generate a greater signal on thinner items (say a hammered silver coin) because a high frequency needs less surface area to cause a large signal.

 

[Daniel A.]

If you were to take a thin gold chain and put it on the ground the only machines likely to see it would be the Troy & Tejon as the coil only see's one link not the whole chain.
Some explores and F75s might hit it depending on settings. High frequency machines have the edge on the small stuff and are quick to respond. Dan

 

[GoGoGopher]

I did an air test the other day with my White's Classic II SL, and I used a very thin gold chain with a gold crucifix...It would only register at about 1.5 inches from the coil, and very weak signal...If I was in the field, I would probably pass right over an object like this, as I swing the coil about 1 inch off the surface to begin with...gold rings were registered from 3 to 5 inches depending on size (smaller ring=shallower detection depth)...Silver rings chimed in loud and clear no matter what the size was....I was kinda surprised about the thin chain...I do not understand what you mean by the coil only seeing "one" link of a chain???? Why is this???


HH,

GoGoGopher

 

[Daniel A.]

I'm glad you tried the test each link is a separate target and the coil will only see one not all. Because the Troy at 19.3 kHz is good on low conductors it has no trouble seeing that one link. I had seen on another forum where this test was done at the time the Troy came out one of the field testers had done this and was surprised.
I don't have the skill to explain it but I'm sure UK Brian can as he does know his stuff. Dan

 

[GoGoGopher]

I do think I see what you mean by each link being a separate target, but would the mass of the entire chain be taken into effect???

GoGoGopher

 

[Carl-NC]

The coil sees ALL the links, but it's an overall weaker signal than for a solid target. If you were to grind up a silver dime into shavings, you would still have the same amount of silver but it would be very difficult to detect.

- Carl

 

[Dan-Pa.]

I do know Tesoro products are about the best relative gold chains along with PI units where you break your back digging from bobbi pins to fish hooks to get the small stuff.
I don't know relative the depth issue but for one a CZ runs in a low to high(two freq's) to cover both..Actually feel it has to do with your ground mineralization and might call and talk to one of the Tech's of your favorite brand and they could give you a plausible answer...
Gosh we all worry about depth and one wonders how many goodies we lose to masking so do take the speed of the unit into consideration...

 

[Tetryl]

Low frequencies do have a better penatration, thats why submarines can transmit info from underwater as well as their submearsable emergency location beacons and that too is a fact

 

[silversmith]

Restated; metal detectors like "closed loops". Take a piece of copper wire maybe a foot long, bend it into a circle, strip the insulation off of each end and twist those ends together. Lay it on the ground and wave your detector over it. Your detector will go nuts! Next, un-twist the ends and repeat the test. Hum, where did it go? Same applies to the chain. Now if you stretch the chain around a gallon jug tightly and short the ends together your detector will find it easily, cause you've again created a "closed loop".

 

[UtahRich]

Restated; metal detectors like "closed loops". Take a piece of copper wire maybe a foot long, bend it into a circle, strip the insulation off of each end and twist those ends together. Lay it on the ground and wave your detector over it. Your detector will go nuts! Next, un-twist the ends and repeat the test. Hum, where did it go? Same applies to the chain. Now if you stretch the chain around a gallon jug tightly and short the ends together your detector will find it easily, cause you've again created a "closed loop".

I agree. Another example of the same phenomenon, a gold or silver ring that has cracked where it was resized and soldered gives a very poor signal compared to a complete ring. If you've found one of these rings you know exactly what I mean.

Lower frequency transmissions will travel farther before losing their signal shape and being unrecognizable. The US Navy uses an extremely low frequency (ELF) of 76hz give or take 4hz for communications underwater. The land based transmitters are located in Wisconsin and Michigan. The signal can reach 10,000' below the oceans surface. (Any beach hunters out there ready to recalibrate their detectors?)

It is my understanding that higher frequencies are more sensitive to smaller items, but do not penetrate as deeply as the lower frequencies used by some detectors. Until the advent of the multifrequency detectors, you were stuck with whatever frequency your detector was manufactured. Now some detectors let you chose which frequency you want to use by programming or coil selection, and some transmit on 17 or 28 frequencies and take advantage of signal comparison.

Good luck to all of you.

Rich (Utah)

 

[kd8hf]

The Navy no longer uses the ELF in Michigan and Wisconsin. The system was disestablished in 2003 and removed completely by 2008, I believe.

Gary

 

[UK Brian]

Your still stuck as you don't know whats under the soil. Could be a large, thick item. May be a small thin item.

Minelab with the X-Terra series reinforced the fact that they lost the case in the U.K. where they claimed that multifrequency gave more depth when C-Scope demonstrated that in most cases it was better to have a coil optimised to a single frequency.

With the 17 and 28 frequency models they don't scan through all the frequencies but use a few harmonics which then leads to design problems, mainly those of extra sensitivity to iron and external noise.