Multi-Frequency

[Mark-VA]

Why is it that a multi-frequency machine does better in hot highly mineralized ground. I have a few old schools where they discarded the coal waste in the school yards. This material will easily attract to a magnet and creates very difficult hunting conditions for regular single frequency machines. The Minelab Etrac and the V3i are the best performers at these sites so far. In reality I can bury a nickel at 5" deep and it all but disappears from the detection of all machines. I'm confident these areas hold a vast amount of goodies if I ever find a machine that can punch through all the waste signals. Why?

[golfnut]

Why is it that a multi-frequency machine does better in hot highly mineralized ground. I have a few old schools where they discarded the coal waste in the school yards. This material will easily attract to a magnet and creates very difficult hunting conditions for regular single frequency machines. The Minelab Etrac and the V3i are the best performers at these sites so far. In reality I can bury a nickel at 5" deep and it all but disappears from the detection of all machines. I'm confident these areas hold a vast amount of goodies if I ever find a machine that can punch through all the waste signals. Why?

I dont really understand it either, but in comms generally spread spectrum is popular as you can see signals below the noise floor - GPS and CDMA do this.

Minelab have an app note for their intepretation of why spread spectrum is good.

Id guess at, if the ground contamination was common, then for a given target there will be a frequecny which will give the best return from that target. If you aint transmitting that tone, then you done see the target.

Like the V3i from memory it has ~22kHz which is great for small gold jewellery
It has a mid - great for coins etc

and a low which will go real deep on handguns etc

So I dont think multi's get rid of the nasty ground, rather line you up better with the targets within it. ?

S

[Mark-VA]

No one know anything else?

[Bodhi3]

Actually Minelab E-TRAC is not a "true multifrequency" machine as it is supposed to be or, at least, not in the same perspective the Spectra V3i is.
Minelab FBS/BBS patented technologies do work in the Time Domain as Pulse Induction machines while V3i's Multifrequency VLF/IB (or DFX or Fisher Cz21) works in the true Frequency Domain.
Without going too technical, try to picture FBS and Multifrequency VLF as both using a "High Power Light Source" to "illuminate" the ground and investigate targets. Well... Imagine FBS is using the heat correlated to the high power light beam to investigate targets by measuring their temperature's variation after different periods of time and using different "flashing duration" while VLF/IB uses light's intensity and color variations due to targets' interaction.

As you can see, they both use "light" emission, but they use it in a completely different way.

Anyway, at least on a theoretical perspective, FBS should be better performing on highly mineralized soils thanks to its minor impact on Time Domain technology (as with the true Pulse Induction machines) while VLF/IB could loose something in depth. VLF best performances in highly mineralized soils are achieved by single-low frequency machines. The lower is the frequency, the better will be the penetration of the ground. And single frequency detectors also have optimised TX power while in Multifrequency this won't happen.

Hope I was useful and forgive my poor English...

Leonardo/"Bodhi3" (Italy)

[Carl-NC]

Why is it that a multi-frequency machine does better in hot highly mineralized ground. I have a few old schools where they discarded the coal waste in the school yards. This material will easily attract to a magnet and creates very difficult hunting conditions for regular single frequency machines. The Minelab Etrac and the V3i are the best performers at these sites so far. In reality I can bury a nickel at 5" deep and it all but disappears from the detection of all machines. I'm confident these areas hold a vast amount of goodies if I ever find a machine that can punch through all the waste signals. Why?

Could be the correlation of responses between the 2 or 3 frequencies. That is, if they correlate (nickel) it beeps, if they don't (slag) it don't.

Actually Minelab E-TRAC is not a "true multifrequency" machine as it is supposed to be or, at least, not in the same perspective the Spectra V3i is.
Minelab FBS/BBS patented technologies do work in the Time Domain as Pulse Induction machines while V3i's Multifrequency VLF/IB (or DFX or Fisher Cz21) works in the true Frequency Domain.

They're done differently, no question, but BBS/FBS is more akin to freq domain than PI. Speaking to BBS and assuming FBS is the same, 2 frequencies are transmitted: 3.125k and 25k. The TX currents are triangle waves instead of sines, so they are continuous waves like VLF and not discontinuous like PI. Unlike most VLFs, the demods are "partial wave" demods as opposed to full-wave demods. That is, they sample/integrate portions of the RX signal. Yes, that is akin to PI, but still much closer to what traditional VLF designs do. If you took BBS and eliminated one of the frequencies, you'd swear it was a normal VLF.

[deemon]

They're done differently, no question, but BBS/FBS is more akin to freq domain than PI. Speaking to BBS and assuming FBS is the same, 2 frequencies are transmitted: 3.125k and 25k. The TX currents are triangle waves instead of sines, so they are continuous waves like VLF and not discontinuous like PI. Unlike most VLFs, the demods are "partial wave" demods as opposed to full-wave demods. That is, they sample/integrate portions of the RX signal. Yes, that is akin to PI, but still much closer to what traditional VLF designs do. If you took BBS and eliminated one of the frequencies, you'd swear it was a normal VLF.

Just the same situation with this "square wave pulse induction" .... we can process this signal both in PI and VLF manner

[golfnut]

A clip from Mr C's write up

" Minelab’s Sovereign, Excalibur and Explorer units use a more advanced transmit signal

consisting of multi-period rectangular waves, which gives more useful information (more frequencies, in effect) than square waves. Themajor advantage results from having several different frequency R signals. These can be used to more accurately determine time constantsof targets because these different frequency R signals are not contaminated by soil mineralisation X signals, unlike the more common VLFdetectors which use R and the mineralisation contaminated X channel to determine the target time constant. In essence, targets with shorttime constants produce larger high frequency R signals than low frequency R signals, whereas with long time constant targets, the lowfrequency R signals are larger than the high frequency R signals. Thus, the ratio of the low frequency R component to the high frequencyR component gives a measure of the target time constant without interference from the large soil X component. In addition, it is possibleto extract a better assessment of the ferrous/non-ferrous nature of a target using multi-period rectangular waves by measuring X whenthis target component is maximized during a particular period of the multi-period rectangular signal. No equivalent such period occurs in aVLF system. See Chapter 2.9 for more information on Minelab’s BBS and FBS ferrous target processing. This results in greater accuracy of

discrimination at greater depths."

[Davor]

Pure unadulterated marketing gibberish. Long version of "it works against all odds"

[Paul99]

Pure unadulterated marketing gibberish. Long version of "it works against all odds"

The leader of the boys club has spoken again! Seems like you have nothing intelligent to reply, and a bystander would think you are wanting to stifle discussion on anything you don't understand?

Lets see you put your detector design up against the CTX3030, and I'll put money on what works best.

[Mark-VA]

My hunting buddy will have his new CTX 3030 tomorrow. We are very excited about this baby. I had the Etrac last year and it did better than any machine I've ever had in our bad ground areas. The V3i is also a good performer at these locations. I'll keep all posted on how well the CTX does.

[Davor]

anything you don't understand?

Which part of diddle-doodle power hog I did not understand?

[WM6]

The leader of the boys club has spoken again! Seems like you have nothing intelligent to reply, and a bystander would think you are wanting to stifle discussion on anything you don't understand?

Lets see you put your detector design up against the CTX3030, and I'll put money on what works best.

Agree, it has best submersible GPS ever.

[golfnut]

The basics of the Tx drive look fairly simple on exp2 i.e. fast, not so fast and slow and back.



S

[Paul99]

Which part of diddle-doodle power hog I did not understand?

Who would know. All you did was make a derogatory comment. You have offered nothing of relevance to the discussion.

You are amusing, Davor. You want people to believe you are a "scientist", yet you don't seek knowledge and the facts. You are happy to discredit without understanding what you discredit. You talk as if you are the uncontested font of detector design knowledge, yet you have added nothing of relevance to detector design.

Your statement "Which part of diddle-doodle power hog I did not understand?" suggests to the reader that you understood everything in the extract from Candy's paper presented in Golfnut's post #7 above. Accordingly then, considering you state the content Golfnut reproduced from the Candy paper is "Pure unadulterated marketing gibberish" would you like to explain your understanding of the difference between square waves and multi-period rectangular waves with respect to Candy's statement of "more frequencies? See if you can back up your ridicule!

When you present the science to discredit Candy's statements re more frequencies from multi-period rectangular waveforms compared to square waves, there are a few more concepts presented in the Candy extract above that you might also like to present the science to discredit.

I can see us all having a far better understanding of whether ML's FBS has any merit after you present your explanation of waveform frequency content Davor. Are you up to it????

[Davor]

First off, I'm not a person of marketing gibberish background, and you are right, such empty pile of near to meaningful phrases put into so many words is most certainly beyond me.

As for diddle-doodle power hogs, yes, they need a lot of marketing push. In a way I sympathise with people entrusted with task of selling meaningless stuff.

Multitone technologies make some sense on difficult ground, yet there is no mention of true benefits in the above mentioned pamphlet. Only various "possibilities" that are most obviously lost in diddle-doodle human interface.

I believe there was nothing derogatory in my initial post. A passage I referred to is absolutely meaningless in any technical sense. It may serve some marketing purpose, which obviously did not work on me, but otherwise there is nothing inside that will ever explain any facet of this technology. I'm not religiously tied to any metal detecting company, and so far I'm incapable of sucking to something like that.

I've seen videos of those monstrosities in action though.