If in real close proximity to iron, and you want non-ferrous unmasking - I think it is most important to use some discrimination with iron volume and multi-tones (2/3/4/5-tones or pitch) vice full tones. Use of disc with targets in close proximity to iron will keep the machine form "down averaging" visual and tone target ID (large iron especially will drag down the target id of a non-ferrous target). Why multi-tones or pitch vice full tones? If you use discrimination, then there is no iron volume with full tones and you will get no iron audio whatsoever from the discriminated region. I find that having a little iron audio when unmasking helps you better discern the masked target as you move the coil between the iron and the non-ferrous target. I personally like pitch vice mult-tones when unmasking. I would suggest using either pitch or two-tones (essentially setting up a ferrous/non-ferrous unmasker). Pitch has the advantage that it can be set to really pop out from the iron volume by setting the base frequency high. The pitch volume intensity will change depending on your proximity to the target. Finally, when unmasking I have reactivity set to at least 2.5 (no silencer) I need to do some more detailed experiments to see whether Reactivity of 2.5 or 3 is optimal. Finally, you can up frequency (in my case, I am almost exclusively running the hf coil so I have an unmasker set at 14 khz and one set at 28 khz). I cannot take credit for pitch unmasker - one of our UK Tnet friends suggested it and Calabash and I have been experimenting and refining it separately.
I pulled this V Nickel out of the muck today using my unmasker program (and 9" round HF at 14 khz) when Tnet buddy Cletus graciously let me play hooky with him today at one of his great permissions. We both found some strange odds and ends but no obvious CW period relics that we were shooting for. The corn stubble, iron, and can slaw were conspiring against us (see below) - so the unmasker and gold field tools were put to work in addition to good old hot full tones (no disc) and disc multitones. Great time nevertheless and managing to pull an old coin out of the ground under those conditions made it worthwhile. Actually, just being there made it worthwhile. Can't wait to make it back there when we can swing our coils a little more freely, I know there are some old goodies that site is going to reluctantly hand over.
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