Discrimination issues?

[Derwood]

I just recently purchased the Vista x. I have been metal detecting seriously for about eight years now. I started out with the MXT and then about a year ago switched over to the whites v3i. I use the v3i exclusively for a year and when I switch back to the MXT I realize I was missing quite a few targets with the v3i. and all manual machine like the Vista x is new to me so I have some learning to do. The first day I received the Vista x I went to an old park that has been hunted quite a bit over the years. I found some clad but I also was digging quite a few pull tabs that crept up into the coin range. Themain discrimination was set at 35 and alternate at 40. When I got home I ran it through my test garden and was quite impressed. The next evening I went to an old elementary school that is still in use and found quite a bit of clad but also found a 8 in wheat penny and a 5in 41 Mercury dime. I went back to the park yesterday evening and was getting a lot of pull tabs, square tabs and beaver tails that were coming in with the discrimination set to 45. I had to set it up to 47 in order to get rid of the pull tabs. It did not behave this way at the old school. One thing I noticed was that I had to turn the ground balance up to about 2 o clock in order to get balanced. At the school it was set to 12 o clock. I was digging pull tabs from 5 to 8 in deep and they were clear signals with a nice smooth high tone. I'm not sure what's causing this. Could ground conditions be a factor, possibly have high mineralisation maybe? The park is not particularly trashy a lot of those pull tabs did not have close by targets. I was sure they were going to be coins. Any suggestions would be helpful.

 

[Derwood]

In defense of the Vista x I do recall getting an unusual amount of pull tabs at the same site with the MXT.

 

[Sven]

As soil conditions at different locations change, ground balance needs to be adjusted, higher or lower.
That's why you ended up with two different GB settings.

But, that can also shift the disc reject/acceptance settings. As well as disc performance. As you found out.




Other effects of Ground Balancing

In some soils after GB balancing neutral so no sound difference is heard when the coil is raised and lowered, then increasing to a bit negative or positive
will see some performance gains.

Too much negative GB under some conditions will enhance falsing, but using the right amount can give a user more depth under right ground conditions.

When you ground balance
(clockwise) positive, you are not only discriminating out the sound of ground minerals, some hot rocks, but also some of the targets
sound as well.

 

[Derwood]

Thanks for the response. I'm going back this evening and I'm going to bury some coins and those areas and see how high they read.

 

[vlad]

on minerals (more can change your detectors responses.)
At a certain point in depth not enough signal is returned for an accurate i.d. and many machines will bump up targets a few numbers (or a notch.)
This seems to happen more with low conductors; a tab (disced out) can be bumped up into the IH penny/screwcap range. And a nickle or ring
can suddenly go up enough to be pushed into the discriminated tab zone. Ground balance will absolutely shift points here.
And turning up sensitivity higher can cause rejected targets to be accepted. (This is different that adding transmit boost.)
Air testing is the optimum your results can be good; it degrades in performance when ground is introduced into the equation.
(Ground balance is adding some discrimination.) You may be digging some tabs in some situations, but as more gold rings fall into that area than the nickel zone
gold recovery possibility goes up. (You'd be surprised the white gold and platinum that falls in the foil zone too.)

 

[Derwood]

One thing is for sure. Avista x does hit deep treasure. I went back to that Park last night and found a 12 in wheat penny. I have pound of that area over the years and so have many other people.