Saeed… yes… I have the original F75 that does not have the “Boost Process” possessed by newer F75 models. I have not done much coin hunting with it, but have used it extensively for silver prospecting. Below is a link to a report describing the F75 in that application. Get past the introductory prospecting discussion, and there is quite a bit about operating the F75.
http://www.treasurenet.com/forums/c...5-metal-detector-revised-february-2011-a.html
The F75 is a high gain unit that can be sensitive to high magnetic susceptible ground minerals, and quite vulnerable to electromagnetic interference (EMI) particularly in urban areas. The motion all-metal mode is much less vulnerable to both ground minerals and to EMI.
The first line of defense to EMI is too
set the frequency adjustment to obtain the least noisy operation.
When using a discrimination mode, the second line of defense is to
adjust the level of iron discrimination up to max iron level if necessary to help attenuate or eliminate EMI. The third line of defense is to
decrease the sensitivity level as necessary to obtain stable operation.
Keep in mind that the F75 may still be unstable (chattery) when the coil is held in the air,
but it will be much more stable when the coil is down and moving over the ground.
Coil Selection… using smaller coils can reduce ground mineral issues significantly and dramatically reduce EMI vulnerability. Small coils see less of each type of interference than do larger coils. DD coils see even less ground mineral than do same size concentrics, which improves stability and depth over tough ground minerals. However… DDs are more susceptible to EMI compared to same size concentrics.
Small coils are very lightweight, provide surprisingly good depth for their size, have less target masking issues… that is to say better target separation, are more sensitive to small targets, and certainly enhance target pinpointing. I recommend you acquire the 5” round DD coil for your unit, it is a pleasure to use in trashy park areas and will improve stability to EMI compared to the stock 11” DD coil.
Other considerations to keep in mind:
(a) If you bury coins and other targets in a testplot to determine how your unit performs, the F75’s target ID and discrimination results will dismay you. Similar to urban renewal projects, and cultivated fields, these are disturbed ground targets. Target ID and discrimination will not work properly on anything other than very shallow surface coins in disturbed ground.
Any use of discrimination on my original F75 will tend to break-up disturbed ground target signals beyond several inches depth. To acquire the best possible indication of what can be expected depthwise, use zero discrimination over disturbed ground. Any coins buried beyond roughly five or six inches in my ground will always read either as iron or will jump erratically all over the target ID screen.
Remember that disturbed ground targets will not give you the depth that can be had on targets that have naturally settled into normal undisturbed ground such as in parks and schoolyards etc.
(b) Read the manual carefully and pay attention to the “notch” section. Enabling the first level of iron discrimination effectively takes the unit out of higher gain in the commonly used DE and PF modes = better stability. Any iron discrimination dialed in under “discrimination” will also appear when viewing the “notch” feature. But if the first level of iron discrimination has been inadvertently dialed-in under the notch feature, it will not show up under the "discrimination” feature.
So it is possible to not to notice that the first level has been selected under the “notch” feature. If you then proceed to select the first level of iron discrimination under the “discrimination” feature you are effectively eliminating that iron discrimination and placing the unit back into a high gain condition.
The above scenario is one of the most common reasons that operators complain about the F75’s instability and seemingly cannot resolve it. I see little or no reason to use the notch feature since any undesirable targets can be seen on the target ID meter and ignored.
Jim.
