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F-75 DISCRIMINATION AND NOTCH
BuckeyeBrad Saunders  02/03/10
 
I can’t help but suspect that some folks that are still having problems with “chatter” or supposed instability with the F-75 or 75 LTD might be actually and unknowingly (at least partially) fighting the interaction of the discrimination adjustment and notch setting. I’m sure most everyone is clear that the two adjustments interact somewhat opposite. This has been discussed many times by many people so I won’t rehash.
 

The biggest potential source for noise problems arising from the operating characteristic of the software induced gain increase, which occurs for disc settings of 1 through 5, is the actual status of the lower half of the ferrous range which is ID 1 through 7. This potential for problems is compounded by the fact that the display does not indicate where the detector is really set (given the aforementioned interaction dynamic) for the 7 seconds that the adjustment knob is hot or active. One might do well to reread that last sentence. This means a user may make an adjustment such as, dialing in a discrimination level of 5 or 6, which is a popular “norm” for stability adjustment, and as they are doing so, the display will show a slash through the low end of iron up in the target category area just as it should. They then take off hunting and are still getting a lot of chatter, and maybe even notice that all nails seem to be still sounding off, almost as if they were still running no bottom end discrimination, which as mentioned, evokes the software induced gain increase. How many folks have made that setup adjustment, immediately started hunting, and still had a lot of chatter? I know I sure did early on with the original 75. And as such, besides scratching your head and begrudgingly turning down the sensitivity setting to a sickeningly low level, did you bother to look closely again at the target category grid when the detector wasn’t in the adjustment mode? Did it then surprise you to see the low iron (the “Ir” of iron) without the slash through it even though you knew well you had adjusted for a disc of 6 and saw the slash at one time? I bet you didn’t wait the 7 seconds before you started hunting. Conversely, there undoubtedly are some that have never been aware that when they think might think they are hunting with “0” discrimination and running high levels of dialed in gain, they are actually hunting with low iron notched out which in part and effectively “allows” some of that higher operator adjusted gain level. Any and all of this can happen due to inexperience, or lack of paying attention, or even due to an accidental and unbeknownst notch input which is not that hard to do in the field. Given that, it becomes IMPORTANT that the operator is aware of this possibility and take the time to really confirm the status of the low iron acceptability or rejection while in the hunting mode and not the adjustment mode. Many have commented that rebooting is a good way to insure where one is starting from as far as discrimination and or notch status. This is one way, but the operator needs to be aware that upon doing so, some level of discrimination is preset and thus needs to be considered if in turn wanting some iron notching. For example, my original 75’s comes up from a reboot with a disc of 10 while my LTD’s does so with a 15. The point is that the best starting point, or at least one’s best bet and actual assurance of being in control, is to confirm that both disc and notch are effectively at “0” (disc at 0 and notch showing 1 with no slash over low iron if adjustment knob is hot) when the display is in the hunt mode and then adjust as needed from there. One of the best places to casually learn about this is in your house utilizing the nails in your sub-flooring. They are plentiful, typically and primarily have a lower half of iron ID, and thus afford the person an easy and rather graphic way to do trial and error learning. Of course in doing so inside the house environment, extra low gain settings will probably be required. The bottom line is that the both versions of the F-75 are awesome capable detectors and if this helps just one person progress from “Well, I think I sorta understand and when I get lost, I just reboot” to “I got it…no problem…piece o’ cake”, which in effect moves them that much closer to F-75 mastery, then it has been worth the time and effort in writing this.

Good Hunting!