VLF Detectors And Depth

[Norvic]

On sink rates of coins or nuggets in dry country (all dry where I chase). As some of our dry country dries after the wet,(usually black soil) it cracks, which allows some targets to "fall" down these cracks, but sometimes this soil movement also pushes even solid nuggets further to the surface. Over the years speaking to cattle property owners they comment on how in some cases it even "pushes" the steel star pickets almost right out of the ground.

One such case in a back soil basin whose depth was more then a metre, I scored a 6 ounce solid about 6 inches deep. Nothing else until the ground was pushed to bedrock where the wash was. Can only deduce that nugget was pushed almost to the surface, it certainly did not shed there as it was fairly obvious the black soil came after the gold shed. This phenomena while not common is not so rare in the country I speak of. Well at least this is the only logical explanation I could think of.

[1515Art]

 SOMEBODY will - and if Apple's success in China is any guide, it might not be a low ball outfit - whether Chinese or otherwise.

After checking with my friends it seems selling metal detectors in China might not be such a great market after all, they are a little touchy about their antiquities and all metal detecting type stuff is controlled by the government. Not to say there isn't a market, but not  for the average person in the general population. 

[nevadad00d]

Sounds like the Inverse Square Law.

[auminesweeper]

According to Carl Moreland, Dan Geyer John Plautz and John Earle They say that VLFs are in No way Maxed out regarding Power and Depth.

http://detectorstuff.com/detector-stuff-interviews-the-engineers-of-whites-electronics/

Here's and Article by Dave Johnson about Search Coils,

http://www.fisherlab.com/hobby/davejohnson/searchcoilsessayrevised.htm

[AU_Solitude]

Good reading, thanks! 

[beardog]

All this info reminds me of just how much I love my Infinium LS PI machine. Say what you want about it, it's a soil slayer, dig everything, multi-tone machine. Of course, it does have the iron ID feature by cranking the disc knob around, but who needs that?

I'm "old school". The less bells and whistles the better and the Infinium gives me this. This machine, for relic hunting, should not be overlooked by the deepseekers. It kills on ferous, the slightest sliver of iron, no matter how tiny, shouts out, within an inch or two from the surface. At 16 inches with a bottle cap size object, no problem. (of course, depending on ground conditions)

What's exciting about the Infinium is that it is truly an "all around machine", finding gold as well as any other conductive targets. 

It does have it's quirks and I did have a struggle when I first purchased it (as a matter of fact I hated it for a while) but eventually learned to respect it.

So give me a machine that I can ground balance, adjust TH, throw in some ground tracking and I'm there. It don't even need to have a disc mode either, just learn coil language.

That's why I love this site, this forum. It makes me appreciate the simple things.

[Rick K - First Member]

I had a look at the above links and Carl Moreland's opinion struck me as about summing it up

"CM: No, but what is practical? Do people want to dig 15-inch-deep coins? The reality is that depth is limited by soil conditions and trash. For mild soil with little trash, it is possible to design a super-deep VLF (2-foot-deep coins), but there are few sites where it would be useful."

At the time, Carl was Chief Engineer at Whites, now he's Engineering Manager at First Texas.

Also, Dave Johnson, said in another interview -

"Getting extra depth out of a VLF, multifrequency, or PI machine is very difficult, because these machines follow an inverse 6th power law relationship between signal voltage and depth. If everything else is maintained equal, doubling the depth requires 64 times as much signal. If this is done by increasing transmitter power, doubling depth requires 4,096 times as much battery drain. That’s the basic reason why depth increases come so slowly in this industry.

The biggest impediment to getting usable depth in the ground, is interference from magnetic and electrically conductive minerals in the ground, which can produce signals hundreds of times as strong as that of the metal target you’re trying to detect and hopefully identify. There are several approaches to extracting the metal signal from the ground mineral signal, but they all have their limitations. That’s why you see several different technologies coexisting in the market."

"http://fisherlab.com/hobby/davejohnson/davejohnsonjohngardinerinterview.htm

Interestingly, Minelab's new super detector - the GPZ is not a PI machine, but a new type of VLF.

[auminesweeper]

Having Dug coins at 13-1/2 inches I can agree with what they say about digging coins at 15 inches, It is seriously hard work and if that coin turns out to be a pulltab most folks would not be too happy about that, VDI's are not too clever at such depths and most detectors depth meters only go up to 12 inches, Not that they are ever right unless the ID happens to be correct.

john

[Steve Herschbach]

Yeah well with all due respect to Carl Moreland, Dan Geyer (may he rest in peace), John Plautz and John Earle not a thing has changed since that article was written in 2009. To get more depth from a VLF requires it to not be a classic VLF as we currently understand it. I have never said anywhere above more depth is not possible, just that is has not happened since 1990 (or earlier). I actually do think we will see something soon, but in the form of hybrid technology that blurs the lines between VLF and PI. The GPZ is just such a beast and it does get the depth, but lacking accurate discrimination raw depth has obvious limitations.

[auminesweeper]

Well there are such things being tested at present, so hopefully they will get to market before winter is over and then we can see what can be done, To be polite I think that the VLF market has been left Wanting for quite a few years now and the that market continues to grow but with very little response from certain areas, The Detector in My head is a lot better than the ones in the shops