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I am a big fan of the White's SignaGraph display. A version 1.0 was originally developed for the Eagle Spectrum. The Eagle Spectrum underwent a complete hardware revamp, and was renamed the Spectrum XLT. A more refined version 1.1 of the software was matched up in the XLT with a much better LCD display. The SignaGraph was also used on the DFX, and was largely the same as on the XLT, with the addition of multifrequency options. The SignaGraph was later greatly enhanced on the V models (Vision, V3, V3i, VX3) and renamed the SpectraGraph.

The genius of the SignaGraph/SpectraGraph is the ability to display multiple target id numbers at the same time, and even to choose how the target id number is determined. Here is the SignaGraph explained by its designer, engineer Mark Rowan. More details can be gleaned from the White's XLT User Guide.

Spectrum XLT Engineering Note
The SignaGraph™ "Phase Spectrum Analyzer"

by Mark Rowan

Some time ago, I had a conversation with an avid treasure hunter whose instrument of choice was White's Eagle II SL 90. He described to me a technique with which he could discern pull tabs from rings, nickels, and other desirable targets by listening for some subtlety in the audio response. Then he asked me, "If I can do this, why can't you program the Eagle's microprocessor to do it?" My response was, "If you can do it yourself, why would you want the microprocessor to do it for you?" I mention this as a means of illustrating what I consider to be the metal detector designer's fundamental dilemma, which is, as Prince Hamlet might have phrased it, "To beep or not to beep". More specifically, if you're faced with a target at some depth in badly mineralized ground and the detector has a hard time getting a solid reading on it, what do you do? If you design your detector to ignore the target, and then someone comes along with their El Cheapo brand detector and digs the target, which just happens to be a $10 gold piece -- you're in big trouble. If, on the other hand, your customers find that they're spending most of their time chiseling through eight inches of hardpan and finding bent nails and wads of aluminum foil, you're not much better off. The point I was trying to make with the gentleman who had devised the clever pull tab discriminating scheme was, that if you put too much of that kind of "intelligence" into your metal detector, there are always going to be those targets that you miss because the machine got fooled.

Which brings me, of course, to the newest White's model, the Spectrum XLT. The Spectrum XLT has all of the features, performance, and flexibility of previous members of the Eagle series, plus a new display which makes the instrument remarkably easy to use. It also makes use of a new way of displaying information about targets -- the "SignaGraph™ or "Phase Spectrum Analyzer" -- which shows the operator everything that we currently know how to display about the characteristics of metallic objects in the ground. In this way, we have gone a long way towards addressing the dilemma I mentioned earlier. The Spectrum XLT is a very "smart" detector, but it is also an "honest" one.

Having done the best it can to determine the probable identity of a target, the Spectrum XLT gives you all of the information you need to make your own decision (human beings are, despite what you might have heard, still a whole lot smarter than computers) to dig, or not to dig.

Before I begin to describe in some detail what the SignaGraph™ is and how it works, I should emphasize that you don't need to know how it works in order to use it effectively, and that the best way to learn how to use it.... is in the field. In a very short time you will begin to recognize certain display patterns as being characteristic of certain types of targets. I should also point out that even if you ignore the SignaGraph™ altogether, this instrument still has the audio discriminator, V.D.I. number, that its predecessors had, plus the icons, and some significant improvements in terms of weight, physical size, and ease of operation.

whites-signagraph-visual-display-indicator-vdi.jpg
White's SignaGraph display

For many years, White's has built detectors which identify targets based on a V.D.I. number (V.D.I. stands for Visual Discrimination Indicator) which characterizes metallic objects according to their size, shape, and composition. The V.D.I. scale on the Spectrum XLT runs from -95 to +95. Large positive numbers typically indicate objects which are good electrical conductors; for example, silver dollars will come in at 92. Smaller positive numbers usually indicate objects which, because of their size, shape, or composition, are not as conductive; nickels will read about 20 and aluminum foil may come in near 5. Large negative numbers are typical of targets which are readily magnetized, but which conduct electricity poorly or not at all. Some sands or soils which have a high concentration of ferromagnetic minerals may read -93. Metals containing iron have both magnetic and conductive properties, which causes them to spread over a wide area of the scale, although most typically iron objects will fall in the range -30 to -75.

The V.D.I. reading is an excellent way to determine the identity of most commonly occurring targets, although I might mention in passing that the only 100% reliable discriminator is called a shovel. However, as a famous metal detector engineer once said, "Life is grossly unfair" (actually, there is no such thing as a famous metal detector engineer, and life really is fair, it just doesn't want anybody to know). For one thing, the signal which a detector receives back from even moderately mineralized ground is typically much stronger than the signal it receives from the targets buried in it. This makes determining an accurate V.D.I. number for a target at any substantial depth a very challenging business indeed.

Furthermore, some targets will cause an abrupt change in V.D.I. response during the course of a single pass under the loop; the most notorious of these are the dreaded bottlecap and the dreaded small piece of foil near the surface in bad ground.

Enter, as they say, the Spectrum XLT. The SignaGraph™ is very similar in some respects to the familiar analog V.D.I. meter. The display is calibrated from left to right in V.D.I. units, from -95 to +95. When the loop is passed over a target, a V.D.I. determination is made, and a vertical bar is placed at the appropriate place on the scale; near the right end of the scale, say, for a reading of 78. So far, this is just what an analog V.D.I. meter would do. At this point, the similarity ends.

An analog meter can indicate only one value at a time; with the SignaGraph™, up to 30 readings can be displayed simultaneously. Also, the vertical height of the bars in the display has significance; the height can either be used to indicate signal strength or a running total of the number of readings at that point on the scale ( the operator may choose which of these two indications is to be used). The advantage of this type of display format becomes evident when the loop is passed over a bottlecap or some other flat, thin iron object.

Although the instrument may respond with a loud, clear audio output, and the V.D.I. readout may register a value near the upper end, the SignaGraph™ will tend to "smear out"; numerous segments will appear throughout the display, many or most of them in the negative (typically iron) range. Try the same things with a coin, and you won't see the "smear"; typically you will see 1-3 bars grouped closely together near the top end of the scale. If any smearing does occur, as it might on a deep coin in bad ground, the more accurate readings will stand taller in the display and will tend to persist from sweep to sweep.

Another unique advantage of the Spectrum XLT is the ability to make use of information gathered during the course of multiple sweeps of the loop. For years, clever detectorists have realized that by passing the loop over the target repeatedly and mentally keeping track of the range over which readings appear, and the most frequently occurring numbers within that range, they can achieve the highest possible accuracy on really tough targets. The Spectrum XLT performs this operation automatically.

The standard mode of operation is the so-called "Graph Averaging" mode, in which a continuous count is kept of the number of readings that fall into a particular slot in the graph. This might also be a good time to mention that more than one V.D.I. determination is made during the course of a sweep; sometimes as many as 6 or 8 readings will be taken during a single pass, so it only takes a couple of sweeps for the effect of averaging to become significant. What you will see in the field will be a single bar on the display which will "grow" until it stands out prominently above the other bars on the display.

Although it is not necessary to adjust them, there are a number of controls that allow you to customize the way that the graph is displayed. It can be set up to clear itself on each sweep of the loop, if you find that too much information is persisting in the display for too long. Or, you can configure it to let the vertical bars fade slowly out of view. Even the rate at which this fading takes place is adjustable. If you don't want to be bothered with any of that, then don't be. The factory preset settings should work just fine for almost anyone. For those of you who want to know an explanation of Accumulate, Average, and Fade, one is included in this Guide.

If all of this sounds confusing or mysterious to you, allow me to put your mind at ease. The Spectrum XLT is one of the simplest-to-operate detectors you will ever use. I shall describe just how and why it is so easy to use momentarily; but before I finish talking about the SignaGraph™, I want to say it one more time-- you don't need to be a Nobel Prize candidate to figure out what the display is telling you. The usual response from somebody seeing it for the first time is something like: "Okay, I get it now. Now leave me alone and let me hunt!"

What is it that makes the Spectrum XLT so easy to use? The key is something that is known in the software business as a "menu-driven interface". To implement that, we have used what is known in the display business as "A True Graphics Display". What all of this means to you, the user, is that all of the controls and options are listed clearly in plain English on the display. A flashing arrow appears on the screen next to one of those options; you can move the arrow up or down with the two "arrow" keys on the 5-key touchpad. When the arrow is next to the control you are interested in, you push the ENTER key. That is everything you need to know to run this machine. If you are like me and you hate reading instruction manuals, I believe I can safely guarantee that you will be able to operate the Spectrum XLT successfully your first time out without ever having to open the cover -- although the manual should be extremely helpful if you want to fine-tune the performance of your detector by adjusting any or all of a rather lengthy list of professional options. Incidentally, another name for this method of running a machine is the "point-and-shoot" method; you point at what you want, then "shoot" with the ENTER key to make it happen. Finally, for those in a hurry, there are a number of "shortcuts" designed to make accessing commonly used features as fast as possible.

What makes the Spectrum XLT even easier to use are the factory preset programs (like those in previous Eagles) which you can load with just a few simple keystrokes, following the prompts in the display. These programs configure the machine automatically so that the beginner or casual treasure hunter can expect a great deal of success over a broad range of conditions.

Any attempt on my part to detail all of the advanced features and controls which the Spectrum XLT has to offer would probably leave me with blisters on both of my typing fingers. Suffice it to say that all of the features we have had in previous state-of-the-art detectors are here in this one, plus several new ones. Most of the features are there because somebody asked for them -- the moral of the story being, keep those cards and letters coming, and we will continue trying our best to give you the kind of detector you really want.

Mark Rowan was a Senior Engineer for White's Electronics, Inc. Mark holds degrees in General Science, and Electronics Engineering Technology, and is a graduate of the University of Oregon. His background includes satellite communications and RF test and measurement instrumentation.

whites-signagraph-display-examples-spectrum-xlt.jpg
White's SignaGraph examples from Spectrum XLT manual

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  • Steve Herschbach changed the title to White's Signagraph Display Explained

There are a lot of feature similarities between the XLT/DFX/V3/V3I/VX3.    I often reference DFX docs to help further understand my V3 features as many of the performance features are the same.....maybe setting differences but actual functionality is the same...ie. Hot Rock Reject for example.

Thanks for including this XLT information.   

HH
Mike

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I have a DFX. When I first purchased it I read the Owners Manual but much was over my head at the time. Purchased " Digging deeper with the DFX" by Jeff Foster. That helped a lot, and I was very impressed with that detector. I understand much more due to this site. Thanks!

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5 hours ago, Mike Hillis said:

There are a lot of feature similarities between the XLT/DFX/V3/V3I/VX3.    I often reference DFX docs to help further understand my V3 features as many of the performance features are the same.....maybe setting differences but actual functionality is the same...ie. Hot Rock Reject for example.

Thanks for including this XLT information.   

HH
Mike

I love these kind of tech notes, and often information detailed in earlier models is sometimes left out in later models as not "new" anymore. I'm pushing it as far as copyright goes reposting some of this stuff I have archived over the years, and which seems to have disappeared as time goes on. This was all on the White's website or in their informational pamphlets once upon a time, but is all long gone now. Anyway, I'm going with the "reposting for historical and informational purposes only" excuse because I hate to see this stuff get lost over time.

I just added the notes on Accumulate, Average, and Fade on a separate thread.

whites-xlt-metal-detector.jpg

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Thank Steve! makes me appreciate the $100.00 XLT i purchased in the pawn shop. asking amount was $250.00 but would not power on. While the salesman was busy with another customer i pulled the battery out and saw the corrosion inside the compartment. After i took it home i ordered a new battery for it and found it works like new. When i removed the coil cover it also had sand inside...just a bonus.

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A few updates made to the original post. I indicated that the SignaGraph display was originally developed for the White's XLT. Not quite. White's was a genuine innovator in digital metal detecting, with the first true digital model, the White's Eagle. As shared in Mark's notes, the original Eagle models had a very basic display. The SignaGraph first appeared in the last version of the Eagle, the Eagle Spectrum, the first White's detector to bear the Spectrum moniker. The SignaGraph was thought of as a "Phase Spectrum Analyzer", and that is where the "Spectrum" part of the name derives from. The Eagle Spectrum had the old larger control box powered by four C cells.

The Eagle Spectrum was very short lived however, as this is when White's was making the move to smaller control boxes powered by eight AA batteries. This set the stage for most everything else that followed, and the White's XLT was one of the first beneficiaries of the new design. The slimmed down Eagle Spectrum powered by eight AA batteries and with a better LCD display was renamed the Spectrum XLT, and then simply XLT.

Here is the ad for the new Eagle Spectrum touting the new SignaGraph display. Click for a larger version. And here is the Eagle Spectrum owner's manual, where one can see the basics of what later became the XLT, then DFX, and the V series.

whites-eagle-spectrum-ad.jpg

whites-eagle-spectrum-metal-detector.jpg

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The Signagraph is one of the most useful visual signal indicators ever devised.  It's a very logical and elegant solution.  On analog metered detectors, the operator can watch the needle "flickers" over a bad target and mentally keep track of where the needle pauses for a split second as it passes over the target, which is a trick I learned with my 6000D back in the 80's.  The Spectragraph basically does this trick for you.  When I upgraded to the new XLT, I immediately took to the Signagraph because the logic was the same, just presented a whole lot easier

The V3i I use now, has the Spectragraph - a direct descendant of the XLT's and DFX's Signagraph.  As far as I know, the V3i is the only detector on the market ...er, recently on the market ... that has this Signagraph capability.  The MXT has the probability indicator, which at first glance is similar, but it actually operates on an entirely different principle.  One of the upgrades to the MXT that I badgered White's to do, was incorporate a true Signagraph into the MXT, which would have made the MXT even more killer.  

The Signagraph was and is a great idea, and one of the many reasons I will never part with my V3i.  With the V3i, you have so much control over the way Signagraph presents the information, which makes it even more useful and fun to use.  I wonder why the idea never really caught on with other detector models/manufacturers?  

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11 hours ago, Wayfarer said:

I wonder why the idea never really caught on with other detector models/manufacturers?  

More to the point, why did White’s abandon the concept after the V3i/VX3? I always wanted a 50 kHz XLT type nugget machine, but as soon as you say nugget machine they take away all the features.

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