Decipher Questionable Signals with Minelab FBS Metal Detectors, page 2
How To Recognize Ambiguous Responses To Coins Close to Nails with Minelab E-TRAC
With Minelab's FBS technologies, a signal is analyzed from a wide range of responses - 28 in total. This allows the E-Trac metal detector to analyze 28 times more target information than a single-frequency detector is allowed to process, and, therefore, the target identification is not only considerably more accurate but also remains that way under adverse metal detecting conditions.
Superiority of the Minelab FBS detectors to other brands' metal detectors also manifests itself in situations related to QUESTIONABLE responses to coins lying in close proximity to iron nails. Metal detectors of other brands do not have such effective means for dealing with ambiguous signals. The E-Trac's Smartfind system along with the FBS technology make it fast and simple for an operator to distinguish responses to good targets from iron false signals.
Upon hearing a questionable response of the Coin+Nail type (described on previous page), you should employ the following E-Trac features for signal analysis:
1) QuickMask's Smartfind window which shows the Target Crosshair position and the target's FE-CO properties on the screen - a 2-Dimensional Phase-Shift Scale;
2) "SIZING" option of the Pinpoint mode (activated by pressing the Pinpoint button on a Control Panel);
3) Depth Gauge with its range of 0-30cm (0-12 inches) from top to bottom.
To analyze an ambiguous target signal, you should follow these steps:
1) Switch to the QuickMask screen (an example of the QuickMask Discrimination pattern is shown here) by pressing the QuickMask button to open the Detect Screen Quick Menu);
2) Sweep a search coil, with extremely narrow and slow coil movements, over the signal spot. Make sure you get the most stable FE-CO reading by approaching the spot with a search coil from different directions or simply TURN 90° on it.
3) As soon as you start getting the most repeatable response, keep moving the coil over that point without changing direction or raising the coil, and look where the Target Crosshair is located in the Smartfind window:
• If it is in the lower right corner, you have less chances to dig up a coin.
• If the cursor is somewhere between the FE-17 and FE-28 lines, your chances to dig up a coin are a little better.
• If it is "hovering" over one of the "coin spots" inside the Conductivity area located above the FE-17 line, it is time to start thinking about calling your detecting buddies over to look at your cool coin find. :)
4) Now you need to keep an eye on the FE-CO readings - this is the most important part of the process. Do not pay much attention to a Fe number as its values will be fluctuating vigorously with every pass of the coil.
This occurs only to the Fe numbers, especially of targets buried deeper than 4 inches, because the Fe numbers represent the target's magnetic properties, and if the coin's response gets affected by nearby iron junk, the coin's Fe reading will be influenced and distorted by close presence of magnetic material. This is why the Fe values are not considered reliable and should not be used for identifying coins, especially deep ones.
The Conductivity readings are usually more stable in cases like this, and, therefore, they play a KEY ROLE in analyzing the target properties, especially of those targets that are lying deeper than 4 inches underground. If you notice that the Co value changes only by 1-4 units with every sweep of the coil, or has the same reading upon every third, or even fourth, sweep, you start calling your buddies over.
5) After you are done with that, make sure that your target is not just a large steel bolt or anything else of a large size. Press the Pinpoint button and pinpoint the target. Do not activate pinpoint when a search coil positioned directly over the target, or the target will be masked out by autotuning feature (for Pinpointing procedure, refer to pages 33 and 77 of the Manual).
While pinpointing, determine the "size" of an audio response and observe the Depth Gauge. Keep in mind that this gauge is factory-calibrated only for coin-size objects. And make sure that you are not pinpointing a rejected target near the potential coin-find because 1) the depth gauge is updated for rejected targets as well, and 2) Discrimination patterns of Smartfind and QuickMask are temporarily disengaged during pinpointing, and you may confuse a coin's depth indication with indication for a junk target. If the gauge indicates large depth, and the audio response is also "large", or the depth gauge shows no depth, and the size of the "screaming" response is larger than your search coil, you better drop your "project" and start running away from fast approaching buddies.
Here is another tip for pinpointing a questionable target: if, during pinpointing, the most strong audio indication of the target is slightly off to the side from where the coin-like signal was initially "picked up" in normal mode of searching, the target is most likely a wrought iron nail with a large nail-head.
But if pinpointing indicates a coin-like object right on the spot, there still will be some time left for you to recover the coin before you hear "Lemme see that!" from your buddies standing by. It usually takes an experienced detectorist a couple of minutes to complete all five steps of this procedure, and less than 30 seconds to recover a coin with use of an electronic pinpointer, probe or inline probe.
This procedure is very easy to do and will become your second nature after some practice. And you will sure develop your own technique and come up with some tricks for analyzing the dubious responses of coins. The major rule in dealing with questionable signals is simple: if you notice any consistency in the target's CO readings, and you hear the high-pitched tone, dig the target!
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