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VDI not reading correctly

J

Jim D

New member
Hello I,ve been having a problem with older coins not showing a correct VDI while in the ground. Before I got the V3i upgrade it was ok.
For instance yesterday I got a 81 to 83 vdi signal 5" deep, thinking I may have a silver dime and found a Indianhead penny witch when out of the hole
read correctly 54 to 60,put back in the hole again read lower 80,s again. I tried different programs,, same results Anybody else have this issue
Had same problem couple wks ago with older wheaties,, If just a few nos.off wouldnt be too bad but an Indian reading in the 80,s. Does anybody
have any solutions?

Regards; Jim D
I
 
Is this your first metered detector?

HH
Mke
 
Chances are the V is giving you the correct VDI by what it is "seeing". By putting the coin back in the ground and getting the same results indicates something in the ground is being averaged with the coin raising the VDI. I could be a mineral pocket, multiple targets, halo or anything else. Don't rely solely on VDI's as to dig or not, or what the target might be, it is only a tool to help you make that decision.
 
VDI numbers aren't always 100% - especially at depth and/or mineralization. Try this - next time do a manual ground balance - then rescan target - if vdi changes significantly that's your problem - drift - if using locktrac need to gb more often/and/or offset +/- - if using ground trac - need to adjust accordingly - probably faster. Even with these adjustments - vdi's are still affected by age/decomposition of coin - depth - mineralization and other variables - that's why so many people dig iffy signals.
 
I too found the oddity, if you can call it that, when I was testing a new V3i on both a unburied and a buried coin. I had a nickel on top of the ground, using a custom coin program, and it was consistent VDI of 19. I'd buried a nickel some time ago at 4", and the program kept reading it a 22, with an intermittent 19 in one swing direction, using the same custom coin program. I could go the the built-in Coin and Jewelry program and get the same readings I got on the surface nickel, VDI of 19. consistently. There's something odd with that IMO. martin
 
As Larry said there is nothing odd about it. As I said in an earlier post I got 12 nickels out of a hunted site. 10 of the 12 did not read 19, many read 22. Why did I get them because people think VDI are perfect and are not affected by G/b, ground and depth. This is not particular to Spectra. The MXT is a nickel getter and the V is every bit as good. Forget air tests.
 
rcasio44 said:
As Larry said there is nothing odd about it. As I said in an earlier post I got 12 nickels out of a hunted site. 10 of the 12 did not read 19, many read 22. Why did I get them because people think VDI are perfect and are not affected by G/b, ground and depth. This is not particular to Spectra. The MXT is a nickel getter and the V is every bit as good. Forget air tests.
Click to expand...

I must still ask though...if the preset coin and coin & jewelry programs consistently read a solid 19, yet the customs programs can't,,,why? The only variable here is that it's one of the preferred custom programs that fails to be that consistent. It's gotta be odd in some way. martin
 
Larry you must be right about the high mineral and or the halo effect, I,ve only noticed this problem with older coins 4"
or more the last few weeks. Whats got me stumped is I never noticed it with the V3 on older coins the 4 months I used it
before I updated to the V3i.
I did notice with my Eagle Spectrum years ago ..I dug alot of buf,s and V nickles that vdi,d in the 30,s and 40,s.even
up toward 50. but I know that was halo effect.
CyberSage and a few other guys on another forum told me not to worry too much about it as theirs did that some to but still
makes me curious. I guess I just needed some more imput about it.

thanks to all for your answers

Jim D
 
that makes me wonder if the the adjustment that is supossed to match the particular coil that is being used is set correctly, or if it is maybe a different setting would do better?

You might also try getting the best ground balance you can get, that might have some effect. Adjusting the GB offset might help but i'm not sure. Adjusting the filter and recovery may also help but first i'd play around with the coil matching adjustment... I don't yet have the upgrade so I cannot tell you how to do it.

I hope if you get it so it works as well as the V3 did, you'll let us know how you fixed it.

Julien
 
The coil matching will have not affect on anything but the accurately of the depth reading. The G/B offset also should have no effect. A poor Ground balance will.
 
Julien; I,ll be out checkin adjustments and tryin a few things in the next few days ,if I find its reading more accuratly I,ll let you all know.
I did find a worn redish buff 4" deep about 5 wks ago and it ID 19. also a war nickle 4", it came in at around 23 - 24, a merc 6" came in at a
jumpy 81.
One thing Im going to do is bury the indian 5 in" deep in my yard ( low minerals ) and see how it ID,s on top and in the hole.
I had a good GB and like rcasio44 said the coil match 10" DD adjustment was correct and helps on the depth reading.only.

Regards Jim D
 
There are too many variables when a coin is in the ground to expect that the VDI won't vary. I once found a full set of war nickels on one weekend hunt. They all came out of the same field and I had the same settings on my detector the whole time. Did they all read the same NO. It's a miracle they read as close as they do. The varying ground minerals, iron above below and to the side, the same for aluminum, multiple targets under the coil, interference, etc. all add to variations. I make sure I dig good sounding signals when I get to a site. I don't start rejecting VDI until I see a pattern for that ground and site.
 
Rob said:

I make sure I dig good sounding signals when I get to a site. I don't start rejecting VDI until I see a pattern for that ground and site.

That is some good way of doing business! I do the same thing and I imagine most seasoned hunters do... my problem is I have a hard time stopping mysely from digging targets I am 99% sure are junk... I just can't stand it. Then I start thinking... why don't I just use a Tejon and dig everything above a certain disc point?... why do I need to spend all this time and money to know what I am going to dig when I am usually going to dig it anyway... well, it is because I LIKE detectors. Even if I am digging junk I get a kick out of knowing what kind of junk it is going to be before I dig it... and now and then I am plesantly surprised, and it is sometimes a very plesantly surprised when that pulltab turns out to be an eagle button or a squaretab turns out to be a cuff button... i'm still waiting for the canslaw to turn into a ring, I haven't mastered that alchemy yet, but I am trying! I have a low percentage of jewelry finds but that is probably because of the places I choose to hunt, I mostly hunt relics or older yards in search of silver coins... but i've made a few really nice jewelry finds.

Very good post Rob!

Julien
 
Jim what was your RD set at?
If the recovery delay is set lower, the remaining target signal may have an effect on VDI whereas a longer RD will bypass that decaying target signal.

I run longer RD so maybe that's why I don't notice the problem.
 
I was mostly running RD at 45 but lately been running around 80 for deeper coin searching.
While experimenting before I dug it the first time,all the programs I tried ID the same ( C/J , My custom, Magic,s, couple others) before
I dug the Indianhead at 5" I tried the different recovery delays to see which sounded the the best
and believe 80 was better. I scan the hole after I dug it up and didnt get a signal.
Another thing I noticed that it gave a good smooth signal at one direction and was broken up just a little
the other direction.
Last evening I buried the Indian 5" in my good ground and got around 56 - 60 same as on top before burying it
so my way of thinking is their must have been high minerals content present or the halo effect.


Regards Jim D
 
rcasio:
For hunting deeper older coins I,ve been running recovery delay 80,but with this indianhead
I experimented with it before I dug it switching from 45 to 80 and trying diff programs (my custom,magic,s pro,
a couple others) to see what it would ID,(which all programs I tried ID the same) also it had a clean smooth
sound in one direction,while other direction was a little clippy.
I buried this indianhead in my yard 5" deep where there is very little mineral, The signal was clean smooth 56-60
also about the same on top of the ground.
So likes been said it could have been a halo effect or high mineral or both causing the high ID.

regards; Jim D
 
Well here iam using a time machine from the past xlt,recently started using dc phase to check target Larry helped with that.well started picking up nickels which eluded me before .they should come in around 19 to 23 xlt mxt 18 20 vid nickel for sure but dc phase on xlt would bounce around but noticed on dc phase +10 or +19 or +40 to44 would be jumping in with a lot of negitive numbers jumping in was probably a nickle.I know the v 3 is way past my machine but maybe checking old vid or dc phase chart on xlt or dfx might help.just passing though.
 
As a coin gets deeper in the ground and approaches the fringe area of your coil field the VDI response will start to elevate. The response can even start wrapping to the negative side (-95,-94). This is normal behavior. You can even reproduce this effect to some degree in air testing. Mineralization strength, and lower sensitivity settings can cause this response to vary. I have Wheat pennies buried in a test garden that exhibit this behavior. For me Wheat pennies at an average depth of 5 to 8 inches come in from 83 to 87 on the VDI. Silver Dimes that are laying flat and unobstructed usually hit in the low 90's. I had 0ne start to wrap on me last hunt. It was down 8 inches. Correlate modes allow for easy adjusting to deal with this. If your ground VDI is in the -95 to -93 you are going to have a noisy hunt however.

Jack
 
VDI is dependent on soil conditions. I found the DFX to be more accurate with an adjustable VDI gain control, but the V3 is a superior detector that will find more. If it sounds good, dig it!
 
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