VLF Detectors And Depth

[Steve Herschbach]

I just posted a long screed on the "more depth" thing on another forum and decided to copy it here as applicable....

Des D Wrote: 
------------------------------------------------------- 
> "Steve, 
> 
> May the 6th, Garrett are promising 'More Depth!', 
> from what appears to be the existing platform AT, 
> VLF tech?" 

You know the score Des. Any of us that have been around do. I have not seen "more depth" on a coin since my Compass Gold Scanner Pro with 12" coil. PI etc for gold nuggets is a different matter - progress seen there. 

People confuse the issues and marketers work the gray area. To most people more depth means the absolute maximum depth coins can be detected and accurately identified at. 

Right off the bat I can tell you that max depth here in Reno is approximately half what Tom sees in Florida due to the difference in mineralization. His accurate id on a dime at 10" is my accurate id on the same dime with the same machine at 5". 

That one fact alone makes nearly all online comparison tests of detectors completely worthless to me. It accounts for the vast majority of online debates, arguments, and accusations of bias, etc. Mineralization rules this game, and what works in mild ground does not necessarily work well in highly mineralized ground. What works well in magnetite laden ground does not necessarily work well in maghemite laden ground, and vice versa. 

Even more serious are depth limitations from masking due to adjacent trash targets. 

We hit max accurate id depth for clear coin type targets in milder ground ages ago. However, manufacturers are filling in the gaps for performance in highly mineralized ground and in dense trash and we therefore get more "apparent depth" 

If I have a coin at two inches with a nail to each side, and detector A cannot see the coin because it is masked, and detector B can see that same coin because it has a faster recovery speed, is not detector B "going deeper" than detector A? It can detect a coin at two inches that the other detector can not. By this standard the Deus "goes deeper" than many detectors, but it still won't hit Tom's dime any deeper. 

Or a manufacturer uses a different frequency and a better designed coil to find a coin in my Reno ground a bit deeper. Let's say we are looking for a nickel. The previous model has a concentric coil and ran at 8 kHz. Great for silver in mild ground, not good for nickels in bad ground. So we get new model running at 15 kHz with DD coil. Much better depth on nickel in bad ground. More depth! Maybe not quite as good on silver as it used to be, but let's just not worry about that, hmmm? Bottom line no better depth on Tom's dime in Florida, but the ad can claim "better depth". 

Previous model did not ground balance to salt range. Poor depth on beach. Now ground balances to salt range, "more depth" on beach. But no better depth on Tom's dime in Florida. 

More depth where, on what, under what conditions, and with what trade offs made? Gaining depth in one area often imposes new limitations somewhere else. They never mention those in the ads. 

Minelab's new GPZ has technology that allows it to pick up certain spongy, wire gold type specimens that a GPX 5000 cannot detect when sitting on the coil. If a detector cannot detect something, and another detector can find it at 5", how much deeper is that? 100%? 500%? I have personally found targets with my GPZ at depths 200% to 300% deeper than my GPX 5000 can find those specific wire gold specimens. Minelab largely pulled a number out of a hat and was very conservative, claiming "up to 35% greater depth" than the GPX 5000. 

People hear what they want to hear. People consistently read "up to 35%" and interpret that to mean "35% across the board". The GPZ will not detect a nice, solid, round nugget any deeper than a GPX. The advantage is on specific gold types. So people get up in arms, much gnashing of teeth and pulling of hair ensues, tantrums thrown, all because people chose to ignore what the words "up to" mean. It means once somewhere, someplace, under some conditions, but true and verifiable. It is a true statement. "Up to" can also mean "same as" under most circumstances. 

I get all this. I made my living in marketing and sales. I see right through this stuff but at the same time I do not get angry because I understand it. An advantage is being had, just not for all people under all circumstances. And almost never, under any circumstances, will it mean any more depth on Tom's dime. 

People who ask on the internet "will it go deeper" are just engaging in an entertaining game we like to play on forums that keeps forum owners like me happy by stirring up discussions. Are machines going deeper on a dime in the clear in mild ground? No. But are they getting better, by using better coils or better recovery or better discrimination/ground rejection techniques at eking out finds from the ground, very often finds at shallower depths? Absolutely! And are they easier to handle, more forgiving while doing so, making it easier for novices to get expert results? For sure. We are getting machines that are getting more more finds in places other machines failed, and the machine that finds the coin the other machine missed does "go deeper". But please everyone quit with the nonsense and hearing what you want to hear and reading "more depth" to mean more absolute depth on a dime in mild ground. That is almost impossible without that new patent. 

I love the new machines, I love what they do and how they do it, and playing around with them brings joy to my otherwise boring life. There are indeed advantages to be had by knowledgeable people leveraging a new coil or a new frequency or recovery speed - or combination of them all - to make finds previously missed. I am personally seeking a machine that runs really well at a low frequency on silver coins, and can then be switched to a high frequency to work well on gold. And satisfies my personal tastes for sound, feel on arm, menu structure, etc. Toss in the ability to also run in true multi frequency mode, for beaches, and we are getting close to the perfect detector. The V3i in theory did it but it has its limitations also. The Impact delivers much of what the V3i offers in a more traditional package and operating system, the only thing really lacking being the multi frequency operation. 

So will the new Garrett deliver more depth? I am sure it will on some target under some circumstance in some place. But will it go deeper than existing VLF machines on a dime in the clear? Not if it is a VLF without a new patent number attached. The reality for most of us is I expect an AT Pro with wireless headphone capability built in and hopefully a more readable display for old eyes. Make a great machine a bit better. More depth? Yeah, whatever.

How To Make Yourself Crazy!

[Guest Tnsharpshooter]

A sensational thread.

 

 

[Randy Lunn]

Hi Steve,

This is an amazing thread. As a relatively new member to the forum I am constantly cruising old posts to learn. Thank you for this incredible forum and sharing your vast knowledge and experience. 

Randy

[auminesweeper]

This is such a great thread, But I got thinking with my mind becoming full of "If Only's" because at one time or another we all crave more depth from our machines and after reading a few of the GPZ threads and how it is best described as a Super VLF and then I thought of I wonder what it would take to make a normal VLF ignore the ground in such away that the signal would be able to penetrate the ground to the maximum out put of the machine,

Some VLF's Air test why beyond what any PI does and some VLF's those figures are totally obscene, wouldn't it be great if someone could get that power to ignore the ground and just do it's thing,  Ground balancing is a very cool feature and how it allows the machine to run stable but the machines still can't penetrate the ground like they do in mild dirt or in the Air,

Some people have made posts about doubling the depth and then quoted the power figures required in order to get that power, But what if we did not have to double the power, what if all we needed was a better way to get that power we already have in to the ground, I think the person or company that could make a VLF do that would turn the detecting world on it's head.

This almost sounds like what is going on inside the GPZ but not quite ?  some place I searched back when I owned my sovereign GT It seemed that I could not get anymore depth than 6 to 10" and then the machine decides that it wants to see a small lead toy at 17" using the factory coil, this had me asking my self all sorts of questions and started to give me doubts too mainly How would I ever know if it was searching down deep or not, So I tried bigger coils and found nothing so that helped a bit but this left me wondering how on earth did it see that lead Toy Soldier that deep, I have never repeated such a feat using a standard VLF machine fitted with a standard coil ever since, But it does show that they can do it when all the planets align,

J.  

[longhn]

Steve,

Thank you so much for sharing your knowledge!!!

[Desert Dawg]

I have a remotely located beach here locally on a river, the mineralization is so severe I cannot detect a quarter over 3-4" max with my MXT Pro. This beach was used for a rock concert many yrs ago, I know there is some good stuff to be found on this beach but a vlf sure is hampered by the blacksand in the beach sands. Its also very full of trash from fishermen, sun bathers and the like which is pretty normal for beaches.   Like Steve says above, his vlf depth in Reno is about half what most others experience in the parks they hunt. 

I was initially very excited about Fisher starting a new line of vlf machines with a different form of ground balance, guess that didn't work out as desired since they dropped the CZX project.

[Mark Gillespie]

I might add something that I fell for several years ago.  Tom, down in Florida was promoting the Fisher F75 very heavily.  Explaining how deep it could go, how fast it was and how much more could be found and I,  before thinking had fallen for all the hype, well maybe not hype in Florida.  Now I can say the F75 is a good machine, might go deeper, is faster and might find more but to the levels of Florida, NO.

In the red/orange clay dirt of Virginia, it struggles just like any other of the VLF machines I've had in the past.  I listened to the "you must run this machine hot" to get the depth but not in Virginia or for that matter anywhere the ground is high in minerals.  But in the white sand, no minerals of Florida, YES.

 

 

 

[Steve Herschbach]

On 2/25/2018 at 7:49 PM, phrunt said:

I wonder if the Equinox with multi-iq has changed this very much? Great old thread though, lots of good reading.

Not as far as I am concerned at least.

Mineralization differences are why I honestly pay no attention to most stuff that gets posted as regards metal detector depth. Florida data is completely worthless to me. I may as well air test for that kind of data. It boils down to get the machines and see it with my own eyes. Frankly, it simplifies life. I don't have to watch tons of videos and ask for advice.

If you are a PI user the whole thing about VLF depth gets plain silly. If I really want depth, I will use a GPX 5000 or a GPZ 7000. That's depth! Once you get used to the performance of detectors like that in bad ground all VLF detectors are a distant second. I use a VLF for discrimination, not depth.

Argue about the Equinox versus V3i for depth for instance. To me it is a shoulder shrug because compared to a GPX 5000 they both suck for depth. I use the Equinox because I like the total package and its depth is acceptable for me. But I never kid myself that it is going "really deep". It's just a different perspective I guess.

[kac]

Would air tests be a better comparison to a machines general performance on depth just to compare apples and oranges? Pi usually go deeper on the ground than air, Is that true with vlf?.

[EL NINO77]

If I compare my air-test tests with my less mineralized  ground "1Bar Fe3O4-Tek.G2" -range in the ground, it will be at most lower by about 10-15%,to 20% ... for different types of objects compared to airtest ... on DD coils ...