Pull tabs

[secondstar]

I’ve been hunting almost exclusively in 25 kHz lately using the X35 coil. With ID Norm set to off, I’ve noticed that nickels fall between 69 - 71 with shotgun shells and pull tabs being “elsewhere.” 25 kHz seems to spread out the mid tones nicely while pushing the high conductors way up into the 90’s. This is great for coin shooting IMHO. Start with Deus Fast and set frequency to 25 kHz. I chose to switch to 4 tones and set the 4th tone break at 93 so that copper and silver coinage really sings to me. I’ve been absolutely killing it using these settings, give it a shot!

 

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[vferrari]

I’ve been hunting almost exclusively in 25 kHz lately using the X35 coil. With ID Norm set to off, I’ve noticed that nickels fall between 69 - 71 with shotgun shells and pull tabs being “elsewhere.” 25 kHz seems to spread out the mid tones nicely while pushing the high conductors way up into the 90’s. This is great for coin shooting IMHO. Start with Deus Fast and set frequency to 25 kHz. I chose to switch to 4 tones and set the 4th tone break at 93 so that copper and silver coinage really sings to me. I’ve been absolutely killing it using these settings, give it a shot!

Yep, you sacrifice a little depth with this approach on high conductors, but overall, it is worth the trade off. My ideal frequency for hunting mid-conductive relics like lead and brass is 28 khz using the round HF coil. It does seem to spread these mid-conductive targets better while jamming the high conductors above 90. Also, 28 khz is more reactive to mid-conductive targets, it makes them sing more than the lower frequencies.

 

[SD51]

Because the metal detector is not doing a metallic analysis. It is inferring what the target is based on the phase shift, strength, size, and shape of the magnetic field that is induced into the target by the transmit coil (and subsequently detected by the receive coil). Electromagnetic properties of metals like conductivity and magnetic permeability (which determines magnetic field strength and phase shift of the field induced in the target and "coupling" with the receive coil) and target shape affect the sensed magnetic field of the target which the detector uses to "ID" the target, but it is only a guess as many external factors such as soil type, nearby targets, and target corrosion and damage can distort the field from the "ideal". Also, it just so happens that aluminum pull tabs, nickels, and gold rings of similar size are a very similar in these electromagnetic properties as far as the detector is concerned and the phase shifts are similar, so most metal detectors have trouble differentiating between these electromagnetically similar targets. Higher conductors like copper and silver are much easier to differentiate because they result in large phase shifts, iron is also easier to detect and discriminate because it is ferro-magnetic and this affects the magnetic coupling to the receive coil which can be easily determined by the detector (though field distortion can cause falsing). Some multi-frequency machines like the Equinox can eek out some additional information as the target is hit with different frequencies and behaves slightly differently to each of those frequencies such that there is some additional capability to differentiate between a nickel and a pull tab but corrosion and soil conditions can still fool the machine.

Bottom line: it's complicated, but these mid-range conductive metals like brass, lead, aluminum, gold, and nickel of similar size are hard to differentiate from each other.

vferrari - Thanks for the excellent explanation, well stated!

 

[Cyberdeus]

Some trash items have rectangular sounds, most of colors have a round smooth sound. This video might help in understanding the nuance tones (skip to 2:00).

The guy in the video is also demonstrating the sounds of the pull tabs.