Vlf better for depth and sensitivity than Pi?

[ElectroNovice]

This was posted on an aussie forum referring to a new gold detector to be unveiled soon.
“cannot comment on the technology as yet but VLF has many advantages over PI on the lab bench including superior depth using the right frequency, coil arrangement etc but gets beaten when the ground mineralization comes into play. VLF discrimination is always superior as is sensitivity. The PI design concept really only helps us with its ground handling ability."
What do you Pi people say?
ElectroNovice

[okantex]

I prefer vlf too

I had used russian made old mining detector.it's head's size was twice a mallboro box ( something like 3*10*13cm).in side circuit there were 2,7 pf capasitors .
IMPORTANT ; WE FOUND A GOLD COİN AT 4 METERS DEPT.coin was in side a small soil cup at size of a fist.
but machine was stolen at the time of earthquake in 1999 in turkey.
have a nice day
okan

[_Raz_]

“cannot comment on the technology as yet but VLF has many advantages over PI on the lab bench including superior depth using the right frequency, coil arrangement etc but gets beaten when the ground mineralization comes into play. VLF discrimination is always superior as is sensitivity. The PI design concept really only helps us with its ground handling ability."

It depends how you define 'sensitivity'. If they are talking about sensitivity to very small targets, then I believe VLF detectors do have the edge in that department. However, on a well designed PI detector, with a very short sample delay, the difference is not too great.

As for depth; In my experience, PI detectors have greater depth capability in the real world. Except perhaps for the afformentioned very small targets.

[JC1]

EE

Hi Electro,

Can't say I'm a PI people as I have PI,VLFs,even BFO, so.
But I can comment. Here goes.

cannot comment on the technology as yet but VLF has many advantages over PI on the lab bench including superior depth using the right frequency, coil arrangement etc but gets beaten when the ground mineralization comes into play. VLF discrimination is always superior as is sensitivity. The PI design concept really only helps us with its ground handling ability."

cannot comment---zero points with me, make that negative

many advantages over PI on the lab bench--- I would rather have one that has many advantages in the field as I can find everything on my bench.

VLF discrimination is always superior --- we all know this, nothing to see here, keep moving along.

sensitivity--- define this.

The PI design concept really only helps us with its ground handling ability. ---- well if that is the difference between working and not working then I would say it could be a definite edge.

[Ferric Toes]

many advantages over PI on the lab bench--- I would rather have one that has many advantages in the field as I can find everything on my bench.

I can't.

Eric.

[JC1]

EE

Hi Eric,

Think I know the source of your noise.

Really like the soldering iron perched on top. Too real.

[kt315]

I can't.

Eric.

this chaos in a field? ... originally!

[jackdetect]

Vlf better for depth and sensitivity than Pi?

Hi all,

Vlf better for depth and sensitivity than Pi?


I am not passionate to any metal detecting technique, so, I believe, I can be objective.
After 3 years on forums, I can see one of fundamental mistakes in approach to rating of metal detector techniques or concrete devices.
Nobody doesn’t speak about polygons, field test etc. Air test is good, but is he ever defined some standard signal level for air testing?
Example:

One of my latest VLF devices, with 50cm coil, having these results, for big roman coin 3,2cm diameter (all metal, tune mod):

In air:

70 cm almost noiseless tone variations
50 cm strong signal (useful)

In ground (on my polygon, with grass etc.):

20 – 35 cm max.

So, what is real result?

The same coin, Puls star II with 38cm coil can not see at all. I known, you will say: low pulse frequency, ok.

Thousand times, I was read about Pi stability for minerals. It is absolutely try, Pi usually totally ignore minerals. BUT, PI is always totally unstable for ground. On any foot, you can get useful signal (like from metal), because of variable distance between coil and ground. But in lab, you can not see it, only on field.

Theoretical, Pi can go deep in ground. But he can go deep only for tank, or something similar. What hunters actually looking under ground?

Maybe ElectroNovice wasn’t give good formulation, but after 15 years of intensive work with all type of metal detectors, I only can agree with him.

And I will try to give better formulation:

VLF technology can provide much more advantages (or future possibilities) for treasure hunters then Pi technology (which is long time ago confront with serious and insolvent problems).

Such formulation was born not only from commercial devices testing, which are catastrophic on both side (Vlf or Pi), but from lot of unusual tests with extreme power, extreme coil sizes, different frequency and shields, etc, and also from lot of concrete field tests.

[Ferric Toes]

Hi Eric,

Think I know the source of your noise.

Really like the soldering iron perched on top. Too real.

Hi JC1, and all who might be worried about my bench.

The picture came from a book on analog circuit design. It's always amused me, as I had an engineer whose bench looked just like that - after he had tidied it up!

JC1 - Can you send me your current email address. I tried one I had for you a couple of years ago, and the email rebounded.

Eric.

[JC1]

Sent you email

Hi Eric,

Sent you email, hope still works.

Hi Jackdetect,

I have built some vlfs long time ago. Know alot about em too.
A strong ground signal will put a large signal into the input of a vlf and you have to lower input gain to keep from saturating, now to get back to the sensitivity you had before you have to make up the gain somewhere else later on in the signal processing circuit. This tends to ruin the signal to noise ratio you had before. So have to fix this, and you have to subtract this large ground signal and still detect the small goodie signal which means a large dynamic range in the signal processing circuit to pull this off. Not easy.

My opinion why you haven't seen a better vlf on the market all these years with all sorts of engineers working on vlf.
Nothing wrong with vlfs. They have been used to find lots of treasures. So have PIs.

I wouldn't expect dramatic increases in performance in either technology over a short time period, as has been proven in the past years. Every once in a while someone posts that they have figured out how to make one or the other much greater, never seen anything come out of one of these posts, as it is easier to post this then actually make one.

They both serve their purpose and alot of serious gold and treasure hunters have both. By the way a smaller coil on a PI will find smaller objects then a tank.

[JC1]

Seen the bench!

Hi Eric,

Yea, I have seen that bench before. Don't know if that was Jim Williams or one of the other EDN, Electronic design, or Analog Devices books. But I've seen it before, and spent some time myself sitting infront of a 555 oscope.

[jackdetect]

Hi JC1
With good coil shielding, and coil assembly, you haven’t a strong ground signal.

After ground phase filtering, ground signal almost not exist. But real power of Vlf conception is multi channel processing, and with it, you can filtering anything: minerals, unwanted metals etc.

Performances of Vlf technology are quite good, but manufacturers are going in a wrong way, and not used all possibilities.

I have Vlf design, which can beat any commercial Vlf device for treasure hunters (for deep targets), but I can not post it simple because want to make money from it. I was also tested lot of Pi detectors on my polygon, and neither was capable to see non-ferrous metal on such depth, like my Vlf with 50cm coil. About ground stability, and DISC ability is not worth to compare.

For industry, geophysics and UXO detection, Time Domain EM (Pi) is probably more interesting method, but for treasure hunters Frequency Domain EM (VLF) can give much more, then Pi.

Of course, I must exclude gold nugget hunt, because haven’t enough experience to compare these two methods.

I was see hundreds of Pi projects on forums. But is any going to search with it in real world?

Any place, with peoples from past, having a thousands pieces of ferrous. Any meter having a couple of them. So, what you really can find with Pi machine?

[ElectroNovice]

Thanks for your replies. But how would your VLF design handle the extreme ferromagnetic ground found in australia? And are you saying that a good VLF design and coils would outperform a Pi for depth on non ferrous targets in this environment? If what you say is true then you would have a good potential market for your VLF in australia for those that want to hunt for large nuggets.We know that there are large nuggets that we cannot reach with our present detectors either Pi or Vlf.We know that despite all attempts in VLf and Pi that the limiting factor is still the highly variable,extreme ferromagnetic (with varaiable amounts of conductive minerals as well)ground which limits the S/N,prevents the use of Monoloop coils and challenges the dynamic range of all known circuit topologies.We have ground in Victoria in particular which still defeats us and results in a massive loss of depth and sensitivity. Em interference is also becoming an increasing problem and further adds to a diminishing s/n.The take home message from all this is come to Victoria australia to develop and test any detector.if it works well over our worst ground then it probably work well anywhere.
ElectroNovice

[jackdetect]

In my last post, I was exclude gold nugget hunt.

Such extreme ferromagnetic ground can be serious problem, if is not homogeneous, especially for high frequency Vlf (for nuggets). Multi channel processing (DISC) can not be efficient for small nuggets, and also, simple Vlf ground Ex mode can not deal, so easy, with two different ground phase signals (ground and rock) in same time. But Pi also have same problem.

In Serbia, we also have gold nugget fields, with high mineral content, but I newer try to hunt gold nugget, or designed detectors for it, simple because we have lot of antique everywhere.

[Ferric Toes]

Such extreme ferromagnetic ground can be serious problem, if is not homogeneous, especially for high frequency Vlf (for nuggets). Multi channel processing (DISC) can not be efficient for small nuggets, and also, simple Vlf ground Ex mode can not deal, so easy, with two different ground phase signals (ground and rock) in same time. But Pi also have same problem.

Hi Jackdetect,

Ferromagnetic ground has two primary minerals that affect metal detectors. These are magnetite and maghemite. Only maghemite gives a response on a PI detector, due to its magnetisation lag, or delay, in following the induced TX field. Magnetite, due to its permiability, will distort the TX field but will not result in a signal. However, induction balance detectors, whether VLF or not, give a strong signal on magnetite, because the field distortion alters the balance in the search coil arrangement. This gives rise to the phase changes, which depend on the relative proportions of the two minerals. As PI only responds to the magnetic lag, and the decay (log t) is much the same for laterite soils, basalts, fired brick etc., it is relatively easy to filter out.

Eric.