A few answers Digger. #1 the soil color. #2 its location where he challenged Bart to a match. #3 the lack of black sand (the DARK grey or black color). #4 the lack of hematite (red color). #4 the white silica soil . I've seen lots of his videos and the remarks really do fill in the blanks ABOUT LOCATION, so do the men's accents. Also many people know (exactly) where he does his comparisons. He haunts the East to SE coast and the Gulf where the mineral content is much lower than most other areas. As Keith Wills once told me, "there ain't any minerals in our soil here in Texas at all."
As for the F75, F70, and even the CZ's (most) people don't read the instructions so they drive the power (sensitivity) so far up that they actually hide targets by locating deep iron or lower soil strata (matrix) instead. I'll look for the engineering notes on this.
Here is where to start written by George Payne, but the following one about SENSITIVITY is good too;
http://cleotusrus.tripod.com/Baron/payne.htm
Sensitivity, as its name indicates, only determines the detector's ability to respond to the weakest electromagnetic fields generated by the conductive and ferromagnetic
substances which may range from non-ferrous targets to clods of mineralized material in the ground (read more about Sensitivity on page 1 of my article -
How To Search Around Cellar Holes Successfully). In other words, by increasing the Sensitivity level, you only instruct your metal detector to LET YOU HEAR more weak audio responses emitted by small and deep targets situated within the detector's actual DEPTH PENETRATION (see details in my article -
"Detector's Depth Penetration & What Affects It").
In case of detecting with
maximum Sensitivity on the
high-mineralized ground, the detector is allowed to respond to the ground minerals, and the user hear lots of additional "noise" - the
ground "clutter". Now the user hears anything but the small non-ferrous targets. Their weak responses, even when amplified by the 'Volume Gain", become masked by a mix of interferences such as the high-sensitivity circuit noise, iron falsing of any type including responses to partially rejected targets and, most of all, ground mineral effects including effects of natural magnetic mineralization - all being also INTENSIFIED
The biggest reason that people have trouble with CZ's for example, is because they crank the sensitivity up past 5, when it only hurts them, and causes GOOD targets to be masked. I have only found one RR spike with my CZ in the last 12 years, an no other nails at all. And it was so much better and deeper than my Ace 250 that I gave the ace to my Daughter. She now uses it as a door stop for her closet, and prefers the cheap Chinese made one I bought her
because "it works better."
Agreed, the ATG is a much better detector..
And from here, and this gets FT users into more trouble and greater loss than anything else: ) I believe this is a Minelab Engineer's article
Using too much Sensitivity intensifies not only the ground mineral interferences but also additional signals from nearby rejected targets - all mixing with the target signal, and the target signal strength gets degraded. If too much Sensitivity is implemented, the detector's circuitry is not able to separate the target's response from responses to other targets and, moreover, to the now amplified ground mineral noise. As a result, the detector's Detecting Range is greatly impaired: the detector's circuitry can not recognize a faint signal from a deep coin among the blend of high Sensitivity circuit noise and ground mineral effect. You may want to read more about Sensitivity here -
"Quieter Operation of A Metal Detector vs. Detecting More Deep Coins" (this article is included in the "Search Programs for Minelab FBS Metal Detectors" section), and on this page
How To Search Around Cellar Holes Successfully, page 1.
You can regain the detector's decent Detecting Range by reducing Sensitivity to a level of the detector's stable performance. However, if the ground mineralization is very high, the stability level of Sensitivity may be too low which is not good either. Under such circumstances, your last resort is to replace the current search coil with a smaller one (see details on next page
The post will be of some value though, it's an entry-level learning tool.
