This is from Digger's post on the CTX3030 Classroom:
NOTE: this chart is comprised of TID readings from air-testing hundreds of coins with three different detectors, using the stock coils. Air tests are not necessarily representative of the TID numbers you will encounter in the field. Ground conditions, adjacent targets, angle that the coin is laying, sweep speed and other factors can (and will) affect your results. However, this information should provide a good basis for getting you started.
Remember, when you set specific target properties to be rejected, the detector still detects them. As such, you will be able to see each target's image in the SmartScreen. However, when rejected, the CTX 3030 will not provide an audio response on those targets. Instead, the audio will null out (target blanking) the Threshold. That is just one of the reasons we recommend setting your Threshold to a "barely audible" level. Also note that the TID numbers for BIG SILVER coins will vary with the Separation Settings. So when you build a new Search Mode, don't reject targets based solely on the TID numbers of one particular Separation mode. e.g. 12 FE line.
In discussing this with Minelab, we were provided the following explanation...
Ferrous-Coin Target Separation ID variation for silver dollars
Highly conductive targets, such as US silver dollars, can give different target IDs depending on which Target Separation feature is in use.
E.g. a US silver dollar in Low Trash Target Separation could give a Target ID of e.g. 01.41, whereas in Ferrous-Coin Target Separation the same coin could be e.g. 12.43.
As a target becomes more conductive (either due to its material properties, size or orientation) it begins to respond more and more like ground, therefore a trade-off must be made between too much falsing, due to ground, and the aggressiveness at which highly conductive targets can be correctly identified. The Ferrous-Coin signal processing could have been made to correctly ID highly conductive targets but there would be excessive falsing if there was any ground mineralisation (i.e. ground would respond like coins).
In the real world this would not be very helpful, so a more acceptable compromise has been implemented in the CTX 3030.
By making the Ferrous-Coin signal processing more robust against some (mildly) mineralised ground the correct target ID is limited up to a certain level of conductivity.
The net result of the conductivity limit for highly conductive targets, like a silver dollar, is their ID is shifted to the 12 Fe (12.xx) line, which is where most targets with coin-like characteristics are displayed. A further side effect of this conductivity limit is that there is a difference between the real received signal and the conductivity limited signal produced by the Ferrous-Coin processing. The difference between the two is interpreted by the detectors processing as a 'ghost' ferrous signal, which typically appears in the bottom right of the screen, just like a ferrous target.
Although the target ID between the Target Separation options for highly conductive targets is not consistent, these targets will still produce a target ID at the high end of the 12 Fe line representing a highly conductive coin-like target, which is highly likely to be recovered!
Target Audio
When using Ferrous-Coin, in the example above, if the 01.41 segment was discriminated (rejected), such as when using High Trash Search Mode Pattern 1, then the detector audio will blank, even though the target ID generated is in the accepted area of the screen. This occurs because the Ferrous-Coin Target Separation signal processing is performed in a separate processing stream than the audio signal. Therefore if hunting for silver dollars, or similar highly conductive targets, this area of the discrimination screen would need to be opened (accepted), to hear these targets.
Using the Silver or Coins Search Modes Pattern 1 are good examples of this.
Ground-Coin
Also note that similar Target ID limitations and audio performance occur when using the Ground-Coin Target Separation feature.
Learning the different behaviours of each Target Separation function and in which circumstances it is best to use them will ensure you achieve the optimum performance from your CTX 3030.
