Understanding your by Randy Horton (AKA Digger) for w o n k r eve n l l ” it ” u o d a e “y r u s yo s e l n u . . sure .
Contents Introduction Getting Started Ground Balance Discrimination Coils Practical Detecting Technology 4 5 6 8 Greetings from Digger Product Timeline Product Comparison Minelab’s Documentation 10 11 12 14 16 Battery Status Noise Cancel Channel Threshold Sensitivity Volume 18 20 21 22 24 Manual Ground Balance Auto Ground Balance Tracking Tracking Ground Balance Offset Beach Ground Balance 26 30 34 38 40 Discrimination Patterns X-TERRA TID Chart of US Coins Treasure Talk - Notch Discrimination
Introduction ...
Greetings from Digger Dear Rea der, I was fortu nate to be chosen to test the fir help field st series of Minelab’s metal dete X-TERRA ctors. Sin ce that ti thousand me , I’ve sp s of hours ent trying to how to ma better und ximize th erstand e perform truly ama ance of th zing meta is l detector X-TERRA . Althoug is quite ca h the pable of o “turn on perating a - and - g sa o” detecto technique r, there ar s I’ve disc e so overed th its perform at have im me ance in th proved e sites I h unt.
Product Timeline You can see from the timeline below, that there have been two different generations of X-TERRA metal detectors. • The first generation consisted of the X-TERRA 30, X-TERRA 50 & X-TERRA 70. • The second generation consists of the X-TERRA 305, X-TERRA 505, X-TERRA 705 & 705 Gold Pack .
Product Comparison X-TERRA 30 X-TERRA 50 X-TERRA 70 Application Coin, Relic & Jewelry Coin, Relic & Jewelry Coin, Relic, Jewelry, Beach & Gold Prospecting Detect Modes (1) Coin & Treasure (1) Coin & Treasure (2) Coin & Treasure, and Prospecting Discrimination One factory Discrimination Pattern that can be personalized & All Metal. 12 segment Discrimination Scale. Two factory Discrimination Patterns that can be personalized & All Metal. 18 segment Discrimination Scale.
X-TERRA 305 X-TERRA 505 X-TERRA 705 X-TERRA 705 Gold Pack Application Coin, Relic & Jewelry Coin, Relic & Jewelry Coin, Relic, Jewelry, Beach & Gold Prospecting Detect Modes (1) Coin & Treasure (1) Coin & Treasure (2) Coin & Treasure, and Prospecting Discrimination Two factory Discrimination Patterns that can be personalized & All Metal. 12 segment Discrimination Scale. Three factory Discrimination Patterns that can be personalized & All Metal. 19 segment Discrimination Scale.
Minelab’s Documentation st u j t ’ n Do read ds! r o w the • My first bit of advice is to read the Instruction Manual thoroughly. • Don’t just read the words. • Apply what you read to your particular circumstances. It is important to know how to set up the detector for effectively hunting a specific site. • Gain an understanding of how each of those settings can (and will) affect your hunt. • Learn when and how to tweak your X-TERRA to best accomplish your task.
Getting Started ...
Battery Status The first thing I do after arriving at and analyzing a site is to turn on the detector and make sure I have sufficient battery life. Some detector makes and models use an unregulated battery voltage for transmission. This results in a loss of detection depth as the battery discharges. Not so with the X-TERRA. The X-TERRAs are capable of using 1.5 volt AA alkaline, 1.5 volt AA carbon, 1.5 volt AA non-rechargeable lithium, 1.2 volt AA NiMH rechargeable or 1.
Noise Cancel Channel ise Cancel o N e h t g n i tt While se hold the u o y e r u s e k a l objects ta Channel , m e m e g r a l y om an coil away fr When I am confident the batteries are sufficient to maintain operation, I set the Noise Cancel Channel. Some X-TERRA models do this manually and others do it automatically. Refer to your Instruction Manual to learn how this is best accomplished with your particular detector.
Threshold Threshold settings range from -5 to 25. Having a proper Threshold setting is very important and should not be taken for granted. Where you set yours will depend on how well you hear tones and where you are hunting. For hunting old coins at old sites, I would discourage anyone from using a negative setting. vice is My ad our to set y old at h s e r h T that is l e v e l a .
Another place where a negative Threshold could come in handy is on wet sand at a saltwater beach. Here, black pebbles of basalt act as little hot rocks. They can sound off like pieces of foil and can be very annoying. Having a negative Threshold helps him in this situation. But understand that doing so can result in missing small gold targets (e.g. jewelry chains) and the signals produced by deeper targets may not be heard. One final note on Threshold...
Sensitivity Next, I check my Sensitivity setting. Sensitivity determines how strongly the receive circuit of a detector responds to anything under the coil. By anything, I mean the soil as well as any targets. Sensitivity parameters vary with the model of X-TERRA you are using. The 305 range is 1 - 10, the 505 has a range of 1 - 20 and the 705 can be set anywhere from 1 to 30.
On the other hand, when you are driving in foggy conditions and your view is obstructed, low beams provide a clearer line of sight. If you were to turn on the high beams in fog, you will find that the light bounces back toward you, making visibility very difficult.
Volume X-TERRA 705 manual p.37 One X-TERRA setting that I never change is my Volume, which is always left at the maximum setting. My headphones have volume controls. So if I ever want to turn down the audio, I can do it easily on the headphones. A couple of things I would like to mention are that the different models of X-TERRA have different parameters for audio volume settings. For example, the 305 adjusts from 0 to 10, whereas the 505 and 705 adjust from 0 to 30.
Ground Balance ...
Manual Ground Balance After adjusting my Sensitivity setting, I establish the proper Ground Balance (GB). Once again, each model (with the exception of the X-TERRA 30, which has a factory preset GB) has a different degree of “fine tuning” for Ground Balance. The 50 and 305 offer Manual Ground Balance with settings ranging from 0 to 20. The 505 offers Manual Ground Balance with settings ranging from 0 to 50. And the 70 and 705 offer Manual Ground Balance with settings ranging from 0 to 90.
ce Balan d n u Gro pad + Pad 5 RA 70 X-TER l p.8 a manu - Pad Pinpoi nt/Det ect pad The theory behind manually ground balancing your detector is the same, regardless of model. Your objective is to “tune the ground phase” of your detector to a setting that compensates for the mineralization at a particular site. In other words, you are trying to neutralize the effects of mineralization. This is accomplished by pressing the Ground Balance pad and “bobbing” the coil a few inches off the ground.
Auto Ground Balance If I am runnin with a g fixed G B, I like t o check it ever y few minut es. If your X-TERRA has the Auto GB function (X-TERRA 70 & 705), you can accomplish a proper Ground Balance by pressing the Ground Balance pad, then pressing the Mode pad while bobbing the coil a few inches off the ground. The letters AU will appear on the display, and within a few seconds, your X-TERRA will have set the Ground Balance for you by using the software parameters established within the electronics.
Tracking For those models with Tracking Ground Balance, know that Tracking allows your detector to constantly update the ground phase setting, on the fly. That means you don’t have to set your Ground Balance before hunting as it will “set itself” within a couple sweeps. After a few sweeps, you can either lock in the current ground phase setting by pressing the Tracking pad again, or you can continue to hunt in Tracking.
Tracking Ground Balance Offset ally, in n o s r e P es the sit of t s o o m I like t , t n u A Ih -TERR X y m run slight a h t i w d Groun e v i t i pos e. Balanc A feature unique to the 705 is Tracking Ground Balance Offset. In simple terms, this allows the user to run in Tracking and at the same time, maintain a Ground Balance setting that varies from the one “recommended” by the electronics of the X-TERRA. On the 705, you can adjust this offset to be anywhere from +1 to +15 or from -1 to -15.
Press the + or - buttons to adjust the Offset. For more information see X-TERRA 705 manual p.44 If I am manually setting the GB on my X-TERRAs, I will properly Ground Balance the detector and then lower the ground phase number by a few clicks of the - pad. Now, with the Offset Tracking functionality of the 705, if I want to maintain Tracking and keep it a bit positive, I can insert a -3 (or whatever level I determine I want) into the mix.
Beach Ground Balance For salt water beach hunting, the X-TERRA 70 and X-TERRA 705 incorporate functionality referred to as Ground Balance Beach. Manual, Auto, Tracking & Tracking offset Ground Balance options are all available in Ground Balance Beach. Ground Balance Beach is capable of minimizing the affects of both magnetic and conductive mineralization in the sand. When combined with a Double-D coil, the negative effects of highly mineralized black sand can be greatly reduced.
Discrimination ...
Discrimination Patterns Once the Volume, Threshold, Sensitivity and Ground Balance are set, it is time to decide whether you want to hunt in a Discrimination Pattern or in All Metal. Discrimination Pattern is the term used on the X-TERRA to describe notch discrimination. The X-TERRA offers multiple Pattern options. The number of available Patterns depends on which model you have. Each X-TERRA offers a “factory preset” for the notch segments that are either accepted or rejected.
X-TERRA 705 Discrimination Patterns (28 segments) Examples of accepted targets for each Pattern All Metal Pattern Pattern 1 Pattern 2 Pattern 3 Pattern 4 X-TERRA 705 manual p.
Discrimination Patterns Definitions !!! Ferrous: Ferrous objects/targets contain iron and therefore are attracted to a magnet. Conductivity: Conductivity refers to how well a target allows electrical current to flow through it. In other words a highly conductive target has low electrical resistance and therefore allows current to flow more easily. Conversely, a target with low conductivity has high electrical resistance and does not allow current to flow easily.
ore The m ts egmen s h c ot n e ble , th availa pecific more s get the tar on . cati identifi Also, both the 70 and 705, with 28 segments, will put all targets into one of 28 TID segments. Those 28 segments represent two digit notches. (Counting by two’s from -8 through +48). So again, the difference between the three models of the X-TERRA, as far as TID is concerned, is the degree in which they can categorize targets. The more notch segments available, the more specific the target identification.
X-TERRA TID Chart of U.S. Coins • These TID numbers were obtained by airtest with coins lying flat. • Depending on many factors, your in-field results may vary. • However, as a general rule , your numbers should be within one notch segment. Pictures of coins I have aquired while detecting (Coins are not to scale) TARGET 30 & 305 TID U.S.
TARGET 30 & 305 TID 50 & 505 TID 70 & 705 TID Zinc cent 32 30 32 Two-cent 40, 44 42 42 Nickel three-cent 4, 8 6 6 Silver three-cent 24 24 24 U.S.
X-TERRA TID Chart of U.
TARGET 30 & 305 TID 50 & 505 TID 70 & 705 TID Clad half dollar 44 45 44 Silver dollar 44 45 46 $5 Gold 28 27 26 $10 Gold 32 33 34 $20 Gold 36 36 38 d n o fi t l l S ti d S n o fi t l til * The reason for wide TID variances is due to their metallic composition changing during the years they were minted. Also the change in metallic composition, wear and corrosion (aka patina) also contributes to a wide TID range.
Treasure Talk - My blog posts Notch Discrimination on the X-TERRA Ever wonder what you're missing? Part one: Friday, September 24, 2010 A guide for U.S. coin-shooters A metal detector does exactly what the name implies. It detects metals. Set to accept everything, you will find nails, foil, pull tabs, jewelry, coins, tokens, relics etc. Anything that is metal. In order to avoid digging those targets you don’t want to dig, we implement a feature known as discrimination.
For the sake of discussion, I will make reference to the Target Identification (TID) scale of the X-TERRA 70 and 705. I will also be using the factory values of Pattern 2, to demonstrate my thoughts. Although the X-TERRA 30, 305, 50 and 505 are similar, the notch segments do have a slightly different value. So, if you are using the X-TERRA 30, 305, 50 or 505, adjust the numbers I’m going to provide, to match your notch segments and TID scale.
Treasure Talk - My blog posts Notch Discrimination on the X-TERRA Ever wonder what you're missing? Part two: Wednesday, October 06, 2010 Now that I’ve outlined how the ferrous vs. conductive properties are represented by the visual and audio TID, let’s evaluate some targets. If you turn your X-TERRA 70 or 705 to the Coin/Treasure Mode, and set it to hunt in factory preset Pattern 2, you will be rejecting notch segments -8, -6, -4, -2, +2, +4, +6, +14, +16, +18, +20, +22, +24, +26 and +48.
To get a better idea of what you might be passing over as trash, let’s check out the conductive properties of various items some might “skip over” while detecting. Again, these numbers are based on the X-TERRA 70 and 705 TID, using the parameters of factory preset Pattern 2. Remember, as I mentioned above, TID numbers are not cast in stone.
Audio Tones The next setting to analyze is the number of tones you want to hear. This is simply a matter of preference. And depending on the X-TERRA model you are using, the number of available tones varies. ine the m r e t e d If I can ductive n o c r o a ferrous values of y rt e y p o pr simply b , t e g r a t ar particul a tone ... g n i r a e h nt time u h y m ize I maxim ving to glance a e by not h ok at th o l d n a down display.
Again, the number of tones you set for your X-TERRA is simply a matter of personal preference. If you chose single tone, all targets will provide an audio report at 450 Hz. Regardless of whether you chose two tones, three tones or four tones, targets with a negative TID (ferrous targets) will produce an audio report of 130 Hz.
Treasure Talk - My blog posts Hunting by ear... Audio tones on the X-TERRA Monday, December 06, 2010 With “old” being a relative term, I hunt for old coins at old sites. The part of the world that I live in wasn’t settled until the mid 1850’s. So finding coins older than 1900 is considered to be a good hunt. Many of my favorite spots to detect are old homesteads and farm sites.
This process is fairly simple… but to implement it, your X-TERRA must be capable of operating in the Multiple Tone mode (X-TERRA 305, X-TERRA 505, X-TERRA 70, or X-TERRA 705). And you must be using zero discrimination (or All Metal mode). Although I’ve found that the 9-inch Concentric coil at 3kHz provides the most easily distinguishable low tones on deeply buried iron, all of the coils will do it to a certain degree.
Treasure Talk - My blog posts Regardless of which coil is your coil of choice, make sure you center the target under the coil before working the coil toward you. And remember, for this method to work effectively, you must have all notches set to accept. Rejected notches create target blanking and audio tones will not be provided for those notch segments.
Coils...
Coil Options sa ERRA i The X-T in r detecto unique lly a an liter that it c rational pe switch o ply s by sim e i c n e u freq fferent g to a di changin y coil . frequenc The X-TERRA range is a unique series of metal detectors in that they can literally switch operational frequencies by simply changing to a different frequency coil. In the previous model series, the X-TERRA 30 was capable of using the 7.5 kHz coils. The X-TERRA 50 could utilize either the 7.5 kHz or the 18.75 kHz coils.
(not compatible with X-TERRA 305) 7.5 kHz Concentric 9” 18.75 kHz Concentric 9” 7.5 kHz Double-D 10.5” 18.75 kHz Double-D 10.5” 18.75 kHz Double-D 10” x 5” 7.5 kHz 6” Concentric 18.75 kHz Double-D ic coil Concentr Transmit winding Water resistant 9” Waterproof Concentric Best ground coverage 3 kHz Best pinpointing Size Large/deep targets Type Medium targets Freq.
Coil Options coil Double-D ric Receive winding Detection field front to b ack ent 6” Conc Transmit winding ” x5 0 1 -D ble Dou With the Double-D coil, one “D” is the transmit wire winding and the other “D” is the receive wire winding. This is easier to understand when you think of the coil as being two capital letter D’s, with the right side facing properly and the left side reversed.
Coil Applications Here are some of the applications I use each specific coil for: 9-Inch 7.5 kHz Concentric Coil The stock 9-inch 7.5 kHz Concentric coil is an excellent “all-around” coil. It is good for coin shooting, relic hunting and general detecting. It offers excellent depth in moderately mineralized soils. And, it provides excellent target response on targets of all conductive levels. So, if you’ve only got the 9-inch Concentric at 7.5 kHz, don’t feel you have to run out and buy more coils.
Coil Applications Multiple Tone (no targets are masked) Detector coil passing over targets Low tone High tone Low tone Threshold es wav d n Sou Sound changes Part of missing target audio response can be due to a fairly fast sweep. But I am able to maintain a fairly quick sweep speed in All Metal (zero-discrimination), multiple tone, and remain confident I am hearing everything under the coil.
I hunt a lot of old farmsteads. As such, many of them are littered with broken pieces of implements and rusty nails from fences and barns. Simply put, I find these ferrous targets produce a very distinct audio response that is more easily distinguished by my using the 3 kHz coil. When I get an “iffy” target, I simply sweep back and forth over it, while dragging the coil back toward my feet. As the target leaves the detection field, if it produces multiple low audio tones, you can bet it is not a coin.
Coil Applications 9-Inch 18.75 kHz Concentric Coil 9” Conc en tric The 9-inch Concentric at 18.75 kHz is a bit more sensitive to the ground than the other two 9-inch Concentric coils. As such, I’ve discovered that I have to lower my Sensitivity setting to keep it stable. As well, I find that it is more sensitive to lower conductive targets. That is a good thing for small gold jewelry.
If, however, when I properly ground balance the Concentric coil and the ground phase number is less than 28, I find the Double-D coil will hunt deeper and provide a more stable operation. The TID when using a Double-D coil is not as accurate as with a Concentric coil. Especially on the more deeply buried targets. But the Double-D design allows for more coverage per sweep than the Concentric coil, allowing me to cover more area in a given period of time.
Treasure Talk - My blog posts X-TERRA... Controlling the search coil Tuesday, January 04, 2011 When it comes to sweep speed, the X-TERRA is a very forgiving detector. You can operate with a relatively quick sweep in wide open areas, and slow down when targets are abundant. But to gain a better understanding of how sweep technique may affect the quantity of our finds, let’s first analyze the field of detection for both the X-TERRA Concentric coils and the Double-D coils.
Although not to the degree of Concentric coils, I’ve found the field of detection from a Double-D coil also gets “more narrow” (front to back) as target depth increases (see Double-D diagram). To ensure that you are not missing those deeper targets, I recommend overlapping the swath of a Double-D coil by third. Again, this allows you to maintain a maximum field of detection during your hunt.
Treasure Talk - My blog posts If your X-TERRA makes false signals when you change the direction of your sweep, you’re probably tipping the edge of your coil. Again, slow down the sweep speed and keep the bottom of the coil parallel to the surface of the ground at all times. As I near the end of each sweep, I’ll make a wide, deliberate turn with the coil, to maintain my rhythm.
I’ve hunted some areas that were so nail infested, proper target separation required a sweep speed of no more than 6 inches per second. As someone who hunts “by ear”, using multiple tones and minimal discrimination, I find the slower sweep speed allows me to process the audio response of every single target. And by using a controlled sweep, I am able to maximize my hunt time by minimizing the number of false signals. Randy Horton (Digger) You’ll never know for sure... unless you dig it! www.minelab.
Coil Design & Manufacture How to design and manufacture an X-TERRA coil You may think that a coil is just a bunch of wires in a plastic housing, but it is actually a complex and critical component of the overall X-TERRA detection system. Here are some of the details straight from the guys at Minelab about how a coil gets designed and built. Coil Design Coil design is a long and complex task that requires many steps to ensure the coil will continue to work correctly for many years.
The two design teams then combine resources to assess the prototype coils: • Manufacturing multiple prototype coils • Testing and revising electronic specifications • Mechanical testing, including: - Temperature stability cycle testing - Cable stretching and bend testing - Rubbing, vibration and impact testing - Accelerated aging and salt spray testing • Field testing second prototypes using internal and external field testers from around the world • Finalizing specifications and drawings That i
Coil Design & Manufacture Coil Manufacture Due to the wide variation in size, shape, frequency and configuration, each of the eight X-TERRA coils have slightly different manufacturing requirements.
Practical Detecting...
Applying What We’ve Learned (so far!) OK, so now we’ve learned the basic functionality of the X-TERRA. We’ve learned the importance of an accurate setup. I’ve introduced you to the various coils available. And I’ve mentioned the importance of hunting where people gathered. Now it is time to talk a little bit about an actual hunt. thing I The first I arrive do when te is to si at a new urvey s visually . the area The first thing I do when I arrive at a new site is to visually survey the area.
Choosing the Right Coil te I’m The si t to hun t u o b a te defini a s a h on the g n i r a be ill be w I l i co h. ut wit o g n i start The site I’m about to hunt has a definite bearing on the coil I will be starting out with. If it is a wide open area, I’ll likely put on a 9-inch Concentric coil so I can cover the area quicker than if I started with a 6-inch coil.
The Hunt X-TERRA Settings After setting the Noise Cancel Channel, Volume level, Sensitivity, Ground Balance and making sure I’m set up in the proper Discrimination Pattern and with the correct number of tones, I’m good to go. Sweeping the Coil As I walk along, I’m careful to overlap my swaths. On Double-D coils I like to overlap by at least 1/3. On Concentric coils, I try to overlap by 1/2. My swath width depends on the circumstances.
dvice I The best a ne on anyo can give e “right ” finding th ed is to sweep spe rself a build you en , and coin gard practice , practice , practice! Target blanking is caused by the detector losing its Threshold while passing over a rejected target. If you are sweeping the coil and your X-TERRA is silent for what seems like seconds at a time, you’re going too fast and are likely passing over too many close targets to allow the Threshold to reset.
Pinpointing Pinpointing Each of the X-TERRA models offer visual and audio Pinpointing. When you press the Pinpoint pad, your detector switches to an All Metal, non-motion detector, with a visual display and audio tone with volume modulation. Pinpoint Auto After getting an initial target signal, press the Pinpoint pad and slowly sweep across the target from multiple directions.
Pinpoint Sizing - X-TERRA 705 In addition to Pinpoint Auto, the 705 also offers the option of a Pinpoint Sizing Mode. Pinpoint Sizing Mode allows the user to maintain the Sensitivity at a constant level, allowing you to trace the size and general shape of the target. With practice, you will be able to separate coins in areas that are too cluttered for most other detectors.
To Dig, or Not to Dig? My Three Rules of Consistency As I have mentioned , I like to hunt in zero discrimination (or All Metal) with multiple tones. And , I’ve explained why. When I am hunting a site , I live by my three rules of consistency. They are the consistency of location , consistency of sound and consistency of TID. 1. Consistent Location By consistency of location, I am referring to where a target is located in relationship to some sort of marking on the ground: a reference point.
2. Consistent Sound I’ve learned the X-TERRA has a very forgiving sweep speed which I use to my advantage when determining whether to “dig or not”. By varying the sweep speed as I “X” over the target, I am able to work the coil very slowly, while maintaining an accurate TID. On the same token, I will regularly increase my sweep speed while X-ing over a target, trying to make the sound “break up”. If it does, it is usually a deep ferrous target.
To Dig, or Not to Dig? 3. Consistency of TID Having located a target with a consistent location and a consistent audio tone, it is time to check the TID. At this point, I already know if I am going to be digging this target, based on the location and sound. But if those two things “pass my test”, I’ll check the TID primarily to see if it is going to be copper, silver, nickel or gold when it is exposed. As I sweep back and forth across the target again, I take notice of the display.
My Recommendation... Again, practice with coins at home. Listen for the sounds and study the TID for different sweep speeds and varying angles. Once you get an understanding of the language of the X-TERRA, go back to the local park and re-hunt along those sidewalks. Think about it... most of the coins that fell from pockets and hit the concrete, rolled off the edge of the sidewalk. The edge of the sidewalk is vertical, making those coins fall “on edge”.
Gold Prospecting Prospecting Mode on the X-TERRA 70 and X-TERRA 705 is primarily designed to find metal objects in highly mineralized conditions. Particularly gold nuggets and relics. In Prospecting Mode, there are no TID numbers as found in the Coin/Treasure Mode. Instead, targets are identified by a change in the pitch and volume of the Threshold Tone. The operational pitch of the Threshold Tone can be changed (ranging from 140 Hz to 1010 Hz) by using the Tones menu.
Technology...
Minelab’s VFLEX Technology lab’s Here is Mine ation of n a l p x e l a i c offi ology VFLE X techn VFLEX technology transforms the common analogue single frequency metal detector into a fully digital machine including a small computer, called a microcontroller, inside the control box and also inside the search coil. The microcontroller in the control box generates a perfect high quality sine wave. The sine wave is produced in the same way that your digital CD player produces high quality sound.
Also when the detector’s transmit frequency is slightly different to the search coil’s tuned frequency, noise and interference will be introduced, reducing sensitivity and detection depth. VFLEX technology corrects this by adjusting the transmit frequency to exactly match the tuned frequency of the search coil. This is only possible because the microcontroller in the search coil communicates information about the search coil’s tuned frequency to the control box. So if the coil is 3.
Minelab’s VFLEX Technology Control box Capacitor eletrical symbol Conventional multiple frequency VLF metal detector Tuned circuit symbol Winding symbol Search coil Other multiple frequency VLF metal detectors have the tuning components spread between the search coil and the control box, introducing noise and instability. As a metal detector’s search coil is moved close to mineralized ground the tuned frequency of the search coil is affected.
With VFLEX the search coil contains a preamplifier that boosts the received signal before noise can be introduced through the cable. This significantly reduces false signals and increases the detector’s sensitivity, even in noisy environments such as under power lines. Another benefit of VFLEX’s preamplifier and microcontroller in the search coil is that the standard heavy weight twin shielded cable isn’t required. The VFLEX coil cable is a light weight ‘Category 5e’ cable.
My Circular Discrimination Theory Lowest Ferrous/Highest Conductive Earlier, I mentioned the discrimination differences between the three models of X-TERRAs. As I pointed out, the TID numbers on the X-TERRA 30 & 305 range from a low of -4 to a high of +44, the X-TERRA 50’s TID values range from -9 to +45, the 505’s TID values range from -9 to +48 and the X-TERRA 70 and 705 range from -8 to +48.
My Circular Discrimination Theory My circular discrimination theory would likely apply to all VLF detectors with notch discrimination capabilities. But for the sake of explanation, I’ll use the 705 as my example. If I were to ask you what direction, in degrees, that straight North represented, what would you say? Is it 360 degrees? Or is it 0 degrees? Actually, it is both. Take a look at your compass. Many of us think of metal detector discrimination as being linear.
My Circular Discrimination Theory Now, if you consider that piece of ferrite I mentioned, and think about those deep pieces of iron you dug this summer (anticipating a silver dollar because they read a +48 ), and toss in this theory of circular discrimination, you get an idea as to how it happened. You dug a piece of iron that provided a TID of +48. Did it read a negative number after it was dug up? Probably.
Q & A with Laurence Dr. Laurence Stamatescu Dr. Laurence Statmatescu is the inventor of VFLEX technology. He worked as a nuclear physicist in a nuclear research institute in Romania, then moved to Australia in 1992. Laurence completed a PhD in Optics (lasers) gaining experience in electronics and signal processing. He joined Minelab’s engineering team in 1996, with the XT 18000 (the predecessor of the Eureka Gold) being his first project.
Q & A with Laurence Q A Question . Answer. If most metallic targets have both ferrous and non-ferrous properties, what triggers whether a specific target registers in the ferrous range (negative TID numbers) or the non-ferrous range (positive TID numbers) on the X-TERRA? There are three “ingredients” of a target that determin its TID.
Single frequency detectors, like X-TERRA, perform discrimination based on the time delay (phase) of the received (Rx) signal with respect to the transmitted (Tx) signal. Given the way the signals are processed in electronics and in software, non-ferrous objects can only have positive phase angles. This can be shown on a phase diagram. Conductance Ferrous objects generally have negative phase angles, because the magnetic response is stronger than the effect of the inductance and conductance.
Q & A with Laurence Q A Question . In sweeping the 3 kHz low frequency (LF) and 7.5 kHz medium frequency (MF) 9-inch Concentric coils over an old U.S. silver dollar (90% silver), the TID displays a value of 48 at distances less than 2-inches from the coil. At distances greater than 2-inches, the TID is 46. When using 18.75 kHz high frequcey (HF) Double-D coils, (6-inch, elliptical and 10.5-inch round) the same U.S. silver dollar registers a 48 regardless of the distance between the target and the coil.
+ + - Normally, changing the frequency of the coil by a large amount (e.g. from 7.5 kHz to 3 kHz or 18.75 kHz) would drastically change the TID of a target. However, because we wanted the TID’s to be the same regardless of the coil frequency, the correspondence between the phase angles and TID’s for the LF and HF coils has been modified (see illustration on pg. 82) to be similar to those for the standard MF coil. This further distorts the TID “bin” size for LF and HF coils.
Q & A with Laurence Q A Question . Answer. For many metal detectors, implementing Noise Cancel is typically a slight shift in operating frequency. If the Noise Cancel process of the X-TERRA is similar, how much of a frequency shift does each channel of Noise Cancel represent? Similar to other metal detectors, the Noise Cancel in X-TERRA changes the operating frequency of the detector by a small amount around the resonant frequency of the coil.
Final Words...
My Settings When people ask what settings I use, I generally tell them that they should adjust their detector for their site, using the procedure I’ve outlined in this book. Then I tell them I hunt in All Metal, (zero discrimination), with Multiple Tones. All Metal allows you to hear every metallic target the coil passes over. But if I had to pick one specific setting, I would chose to hunt in a Discrimination Pattern with all the notches set to accept.
In All Metal, those deep iron targets are more likely to bounce between the most conductive reading of +48 and the most ferrous reading of -8. Having a specific notch segment established to accept the most ferrous property values (-8) results in less TID bouncing (-8 to +48 ) on deep iron targets. X-TERRA users will find that the higher frequency coils produce more “wrap around” signals than lower frequency coils.
d Review Study the Instruction Manual. Know what functionality is controlled by each setting, and how proper adjustment of those settings will directly impact the success of your hunt. Always check your Noise Cancel Channel and Ground Balance every time you change sites or switch coils. Check your Ground Balance every few minutes. Recognizing that the software application of the X-TERRA is much more precise than our ears, use the Auto features whenever possible.
If you want to find a deep “keeper” that the last person missed, keep discrimination levels low and apply the three rules of consistency; location, sound and TID. As you approach a hunt site, don’t be afraid to think “outside the box”. Instead of just walking around the base of that big tree, try hunting that area that is shady during the late afternoon/evening hours. Analyze the site, plan your hunt and hunt your plan.
Glossary of Terms Concentric coil A Concentric coil has an inner circle and an outer circle wire winding. Its search pattern is cone shaped and can be useful for accurately pinpointing a target. Conductivity Conductivity refers to how well a target allows electrical current to flow through it. In other words a highly conductive target has low electrical resistance and therefore allows current to flow more easily.
Hot rocks Hot rocks are rocks that are mineralized differently to their surrounding ground. For example a highly mineralized rock buried in mildly mineralized ground would be considered to be a hot rock. However, a highly mineralized rock in an equally highly mineralized ground would not be considered to be a hot rock. Ground mineralization Ground mineralization refers to how magnetic the ground is.
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Best Awarded 2009 & Finds Of h finds 2010. Bot 7 Indian were 187 ts. Head cen Western & Eastern Treasures Magazine www.treasurenet.
Success Stories from Minelab Dear Reader, ding your X-TERRA” by Randy Horton. We hope you have enjoyed reading “Understan to www.minelab.com by other Here are some more Success Stories submitted world. successful X-TERRA detectorists from around the Regards from the Minelab Team “ I was daydreaming of how nice it would be to find a coin from the early 1800’s or 1700’s but that will never happen to me because I live in Montana. And WHAM! The next day I find a 1758 penny.
“With metal detector X-TERRA 705 I found these old objects. They are from 3rd century (ROMEMPIRE) 3 coins, 1 silver bracelet, 1 old key, 1 old padlock . The big coin is from Gaius Aurelius Valerius Diocletianus, was a roman emperor from 284 to 305.” Stojan - Macedonia X-TERRA 705 “HOLY CATS MAN its a STANDING LIBERT Y QUARTER . WOW, I was so stoked . I jumped to my feet and held that awesome Quarter towards Heaven and thanked God out loud .
About the Author Randy (or Digger as he’s known) has been metal detecting in the Central US for nearly 40 years and has a passion for finding old coins at old sites. In addition to performing field tests for several manufacturers (including the Minelab X-TERRA series), he also serves as Moderator on the X-TERRA forum at Find’s Treasure Forums. Digger has written several articles, and enjoys sharing his thoughts and tips on various aspects of the hobby.
