Minelab Multi-frequency

[Steve Herschbach]

15 hours ago, Rick Kempf said:

I agree that the recent stuff on multi IQ has been much more informative. But the whole 28 frequency malarkey went on far too long - for decades I think.

Of course it started in a time when the “magic” of metal detectors was very much what was selling them to the hopeful, but about the same time Whites was publishing their engineering white papers on their new units.

It’s not partisan - just pointing out that folks who want to actually know what is going on - and who recognize the need to protect proprietary information - have historically had a very hard time getting decent technical information on which to base their purchasing decisions.

 

From everybody and everyone for decades. What I object to is this idea that Minelab is inherently evil and lies about everything while the rest of the companies get a pass. It gets tiresome. If the best the competition can do is rag on Minelab's advertising methods, well, it's not a good look either. Anyone who thinks this line of inquiry is being pushed purely by frustrated consumers is even more naive than those who think Minelab is going to explain to their competition proprietary details via advertising. I would rather see competitive hardware than counter information campaigns myself.

Oh, there is that cynic again.... 

[Mark Gillespie]

8 hours ago, Steve Herschbach said:

From everybody and everyone for decades. What I object to is this idea that Minelab is inherently evil and lies about everything while the rest of the companies get a pass. It gets tiresome. If the best the competition can do is rag on Minelab's advertising methods, well, it's not a good look either. Anyone who thinks this line of inquiry is being pushed purely by frustrated consumers is even more naive than those who think Minelab is going to explain to their competition proprietary details via advertising. I would rather see competitive hardware than counter information campaigns myself.

Oh, there is that cynic again.... 

The main thing for me is, will it outperform my present detectors.  The answer is yes, but my TDI in bad ground is still my trump card.  But that is not a fair comparison.

 

[LowTide]

Purchasing decisions are based on what works in the ground or doesn't work.  Not on how it works!  If Dong Fong based in Shenzhen China makes a detector that is 25% deeper no one is going to ask(except fanboys of certain brands), how it works or complain about advertising....they will just buy it and be happy it is 25% deeper.

[Xergix]

This discussion intrigued me that in multi-frequency Equinox does not transmit all five frequencies,i thought about the way to analyze the transmitted signal without having to open Equinox,  unfortunately I do not have a spectrum analyzer but only an oscilloscope,  Equinox is a vlf so its signal can be heard by a good microphone, i had done a similar test in the past on Deus,  so the instrumentation used is a 20 Mhz band Fluke 123 portable oscilloscope and a Prologue dynamic Shure microphone.

 As you can see from the picture I placed the microphone in the middle of the coil, in Park 1 I checked all frequencies individually, as seen in the photos, all five frequencies correspond, in multifrequency things change, the graph is noticeably different from that with a single frequency, Fourier does his job, these views are also identical in other mode, excluding Beach 1 and 2, things change in Beach, the visualization is different, at first interpretation, one has the sensation that in all other modes, in multifrequency, there are all frequencies.In beach 1 and 2 in multifrequency something is missing.Probably there are only the most useful frequencies for sea and beach research.

This analysis gives no certainty that Equinox in multifrequency actually uses all or part of the frequencies, but certainly establishes that the use of the multifrequency is different between the terrestrial and marine modes, what then happens in the processing of the signal only knows Minelab.

[groundscanner]

Great visual!  Thanks!

[dewcon4414]

Its possible nothing was missing from beach....... but in fact added... a salt setting the other dont use.  Oooo pretty lines .... thats the extent of my knowledge you just showed lol.

[Mark Gillespie]

On ‎12‎/‎24‎/‎2018 at 10:49 AM, Steve Herschbach said:

The why of it is simple - you are reading things into the careful gaps Minelab leaves in their advertising. I am not reading it the way you are, and so I am not offended because I do not feel I am being mislead. You are reading something else into it and feel unhappy because you feel you have been mislead somehow. It all boils down to debating perceptions of what you think the advertising means as compared to what is really going on under the hood. Since you don't 100% know what is going on under the hood, you just don't know.

All detectors are transmitting on at least one primary frequency and many harmonic frequencies. This can be determined with a scope and if you count harmonics it is just a matter of picking a number you want to advertise when it comes to transmitted frequencies. You have no idea how many are being processed unless you know the processing algorithms.

This back and forth with Minelab and the others has been going on for years. Garrett picked 96 frequencies for a Garrett Infinium ad as a direct poke at Minelab. How many people thought the machine was really transmitting and processing 96 frequencies based on the ad? It is all about transmitted because a PI detector does not receive and compare frequency information. Meaningless fluff, an industry insider joke.

Get your 96 frequency detector right here....

Garrett Infinium ad - 96 frequencies!

Carl Moreland weighed in with his frustration on another thread. White's even gave room over in the V3i manual, probably with Carl's input, to comment on the situation. From the White's V3i Owner's Manual, page 6:

"There is much confusion - some of it deliberate - over how many frequencies a detector actually uses, and whether multiple frequencies are truly better than a single frequency. What defines a multi-frequency detector? What do multiple frequencies really do for depth and discrimination?

A multi-frequency detector is defined as one that simultaneously—or, in automated sequence— transmits, receives, and processes more than one frequency. Some detectors have the ability to operate at one of several selectable frequencies, but they still are single frequency detectors because during operation they can only transmit and process a single frequency. The same is true of detectors that have a control to slightly vary their operating frequency to minimize interference; even though they have the ability to operate at many (slightly) different frequencies, they are fundamentally single frequency designs. Currently, all multi-frequency hobby detectors run their multiple frequencies simultaneously as opposed to sequentially; they are all characterized by having multiple processing channels in the receive circuitry. Therefore, a 2-frequency detector will have two processing channels. Spectra V3i has three independent processing channels; it is a true 3-frequency detector.

This all sounds easy, so where is the confusion? It turns out that (currently) all multi-frequency detectors create a transmit signal that is composed of digital waveforms which are designed to produce peak energies at the desired frequencies. As a side-effect, these digital waveforms also produce undesired harmonic frequencies. Lots and lots of harmonic frequencies, 10’s or even 100’s of them. These harmonics have no useful energy and are not part of the signal processing. So while we can claim to transmit many, many frequencies, we cannot claim to process or use them. Therefore, we could easily claim the Spectra V3i transmits 17 frequencies, or 28, or 39, or 55—we could get plain silly with this. And such a claim would be true, technically speaking, but since all those extra frequencies are not actually used, it would be misleading to make such a claim. White’s chooses, instead, to claim the number of frequencies we are actually using and processing. It may not sound as impressive as a 55-frequency detector, but it’s honest and accurate.

Pulse Induction (PI) detectors also utilize a digital (pulse) transmit waveform, so they transmit a tremendous number of harmonic frequencies as well. So is it fair to include pulse induction as a multifrequency technique? Not really, because PI detectors process in the time domain, not the frequency domain. So even though they use broad-band signals, they are not frequency-based detectors at all. Calling them “multi-frequency” is simply another attempt to confuse the consumer.

Once we get beyond the marketing hype, the real question is: What does multi-frequency do for depth and discrimination? The truth is, any time a detector is simultaneously transmitting more than one frequency, the transmit energy must be divided amongst the frequencies. Therefore, a single frequency detector can usually squeeze out slightly more depth than a multi-frequency design at that certain frequency. But this is an advantage only at one frequency, which tends to favor only a narrow range of targets."

 

These are old debates going back to Minelab BBS and it’s 17 transmitted frequency claim. I reference it all in my discussion at Selectable Frequency And Multiple Frequency

Anyway, interesting subject for armchair engineers and armchair attorneys. Hopefully you all get it sorted out while I am out metal detecting! 

This is another machine I've always wanted to try.

 

[broadfield]

Does anybody know what frequency the VDI number is normalized to?

I assume a target will give the same VDI number regardless of what frequency is used? Multi or Single?

[Chase Goldman]

3 hours ago, Dan Fox said:

Does anybody know what frequency the VDI number is normalized to?

I assume a target will give the same VDI number regardless of what frequency is used? Multi or Single?

There are slight variations but not enough to worry about.  Basically the VDI's are normalized across the board regardless of frequency or multifrequency in each mode.  There is no frequency reference (like the Deus at 18 khz) that the VDI's are normalized to.  

[Xergix]

The waveform taken with the microphone is not the real one, but it is distorted by the dynamics of the microphone, the signal taken with a link has the right shape, and compared to the Minelab chart you can see that it coincides.
In beach mode it is evident that at least two frequencies are missing.