All Terrain General Vs All Terrain High Conductor

[AirmetTango]

On 1/6/2023 at 5:51 AM, fishersari said:

I did an air test between these 2 modes by using a high conductor copper coin (ID-91). The AT general has depth advantage over AT High conductor mode around an inch. Both mode used same setting: sensitivity - 18, recovery speed - 4, ground balance - 0, audio theme Normal + Simple. AT High conductor should go deeper? Did I do or think wrong? Would love to know your thought and if possible same air test to compare result. Thank you in advance

 

On 1/6/2023 at 6:31 PM, fishersari said:

It caught me by surprise that the general mode is deeper about an inch compare to HC mode for high conductive coin. I mean the HC should be deeper than General even on air test?. Assuming its using much lower frequency weight in than the general mode right? I will test it today at relic site.. If general mode is still deeper than HC for high conductive target... I don't know maybe there is something wrong with my machine

I don’t think there’s anything wrong with your machine - I honestly think you’re just seeing a very real demonstration of how air tests can be very misleading. As you probably know, high frequency machines do very well on low conductors (ie, small targets). But in reality, high frequency machines do very well on all targets - high conductors (big targets) as well as low conductors - in air tests. It’s the ground that gives a high frequency machine problems as the ground matrix much more quickly attenuates a high frequency signal. And the more mineralized the ground, the worse the problem gets as the high frequency lights up all the magnetite and other mineralization that a low frequency machine is less susceptible to.  This is why high frequency machines tend to get used for gold detectors (40 to 70 kHz machines targeting small gold, for example), but they get terrible depth in mineralized ground.

Low frequency machines also air test quite well, although for several reasons it wouldn’t be surprising for it not to air test as well as high frequency. Where the low frequency shines is in the ground, for certain sized targets. Low frequency punches through any mineralization better, providing better depth, especially as mineralization increases compared to a high frequency machine…the caveat is, you absolutely will lose smaller (less conductive) targets that the low frequency just can’t hit.

So putting it all together, AT General is weighted as higher frequency compared to AT HC, which Minelab says is weighted to low frequency. Based on what I mentioned above, it makes sense that the two modes will air test similarly and maybe even with an advantage to high frequency depending on the size and/or conductivity of the sample target. But bury a high conductor near the edge of good detection depth for AT HC in highly mineralized ground, and you may be surprised to hear silence when you switch to AT General.

But you don’t have to take my word for it - Steve Herschbach covered this concept in fantastic detail in his excellent post about Target ID versus Target Size here:

Target ID More About Target Size Than Type Of Metal

Further down, @Steve Herschbach even relates a story about his Fisher F75 vs a Fisher Gold Bug 2 that directly relates to your air test. The whole thread is invaluable reading!

 

 

[fishersari]

Thank you for detail explanations and I did buried high conductive coin at one of my relic site, like Strick said the HC has slight advantage over the General mode .Only 1 more possible problem for me to find the answer though before I am satisfied with my machine.. that I can hunt with the sensitivity of 35 with the coil submerge in salt water and what unforeseen ground/target reaction etc, maybe the 35 sensitivity overwhelm the noise, the ground.. I don't know ... but for now I'll run with the sensitivity of 29.

[Steve Herschbach]

On 1/10/2023 at 4:46 PM, AirmetTango said:

 

I don’t think there’s anything wrong with your machine - I honestly think you’re just seeing a very real demonstration of how air tests can be very misleading. As you probably know, high frequency machines do very well on low conductors (ie, small targets). But in reality, high frequency machines do very well on all targets - high conductors (big targets) as well as low conductors - in air tests. It’s the ground that gives a high frequency machine problems as the ground matrix much more quickly attenuates a high frequency signal. And the more mineralized the ground, the worse the problem gets as the high frequency lights up all the magnetite and other mineralization that a low frequency machine is less susceptible to.  This is why high frequency machines tend to get used for gold detectors (40 to 70 kHz machines targeting small gold, for example), but they get terrible depth in mineralized ground.

Low frequency machines also air test quite well, although for several reasons it wouldn’t be surprising for it not to air test as well as high frequency. Where the low frequency shines is in the ground, for certain sized targets. Low frequency punches through any mineralization better, providing better depth, especially as mineralization increases compared to a high frequency machine…the caveat is, you absolutely will lose smaller (less conductive) targets that the low frequency just can’t hit.

So putting it all together, AT General is weighted as higher frequency compared to AT HC, which Minelab says is weighted to low frequency. Based on what I mentioned above, it makes sense that the two modes will air test similarly and maybe even with an advantage to high frequency depending on the size and/or conductivity of the sample target. But bury a high conductor near the edge of good detection depth for AT HC in highly mineralized ground, and you may be surprised to hear silence when you switch to AT General.

But you don’t have to take my word for it - Steve Herschbach covered this concept in fantastic detail in his excellent post about Target ID versus Target Size here:

Target ID More About Target Size Than Type Of Metal

Further down, @Steve Herschbach even relates a story about his Fisher F75 vs a Fisher Gold Bug 2 that directly relates to your air test. The whole thread is invaluable reading!

Could not have explained it better myself! Yes, air tests are good for lots of things, but determining relative depth between machines or even modes on one machine is not really one of them. An air test can help reveal the theoretical max depth you might get in the ground. It is the ground that matters in the end however, as different frequencies and types of detectors (VLF vs PI) are affected by ground at different rates. VLF vs PI is a big one, as VLFs can look very good in air tests compared to PI detectors, but fall flat on their face on in ground targets. It's not that the PI goes deeper in the ground, it is that is loses less depth in the ground than the PI. So in a bad ground situation, you might see a PI lose 10% of its air depth in the ground, while the VLF loses 60%! That's not trivial, that's huge, and it is why I tend to belittle air tests anytime people use them to compare detector depth.