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  #1  
Old 09-02-2008, 09:42 AM
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Default Those pesky ghost signals

I've recently purchased the Whites MXT and couldn't be more pleased with its overall performance and accuracy.Been able to find my fair share of wheaties,musket shot and a Indy (very thin and brittle)that I'm still trying to figure the age one. My question pertains to ghost signals.There are times,mostly in trashy areas where I'll get a full bar on the VDI and great audio signal then initiate the dig and recheck my hole and poof the signal vanishes....Any ideas on why this occurs?
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  #2  
Old 09-02-2008, 09:53 AM
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There is a phenomena commonly called the "Halo Effect". It is sometimes present when an iron object completely rusts away...leaving "ghost" ions in the soil immediately surrounding the object. Digging disturbs this "halo" and the signal disappears.

I've only blamed one for an undiscovered find. Do your audio signal and VDI remain constant in both directions before digging?

There are many experts here who may answer the question better than my explaination, but I'd suspect it's your problem...given the hunting area you described above.

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  #3  
Old 09-02-2008, 10:16 AM
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Yes the audio and VDI have remained constant the two times it happened.Its possible it could be a learing curve thing but I would definitely like to get to the bottom of this issue.
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  #4  
Old 09-02-2008, 10:35 AM
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Quote:
Originally Posted by Mister7 View Post
I've recently purchased the Whites MXT and couldn't be more pleased with its overall performance and accuracy.Been able to find my fair share of wheaties,musket shot and a Indy (very thin and brittle)that I'm still trying to figure the age one. My question pertains to ghost signals.There are times,mostly in trashy areas where I'll get a full bar on the VDI and great audio signal then initiate the dig and recheck my hole and poof the signal vanishes....Any ideas on why this occurs?
Hi Mister7, I have several questions for you:

You say it happens in trashy areas. What coil are you using?

Is most of the trash of a ferrous nature?

Was the machine on auto-track, or did you lock the ground balance after balancing on clean ground?

What was the sensitivity setting?

When you pin pointed the ghost target, how deep was it? How "tight/small" was the target as you swept it in pin point mode (while listening to the pin point VCO signal, did you get a short bleep, or was the VCO sound on the broadish side)?

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Old 09-02-2008, 04:29 PM
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Hi Rudy and thanks for taking an interest in my problem. I use the White's 9.5 coil in that area,the types of trash are full spectrum ieull tabs,screw tops,nails,aluminum cans right down to out right rusted iron and other heavily rusted metal objects.....I keep the MXT on auto trac but have considered locking it in this area because of the wide array of dedris (liteally 250 yrs worth).I would just say to heck with the area accept my gut is telling me there are some neat finds buried there (already found several). My sensitivity setting is at the first factory preset (just below nickle). Thanks
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  #6  
Old 09-02-2008, 05:45 PM
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Originally Posted by Mister7 View Post
Hi Rudy and thanks for taking an interest in my problem. I use the White's 9.5 coil in that area,the types of trash are full spectrum ieull tabs,screw tops,nails,aluminum cans right down to out right rusted iron and other heavily rusted metal objects.....I keep the MXT on auto trac but have considered locking it in this area because of the wide array of dedris (liteally 250 yrs worth).I would just say to heck with the area accept my gut is telling me there are some neat finds buried there (already found several). My sensitivity setting is at the first factory preset (just below nickle). Thanks
If the area is that trashy and littered with ferrous there are several things you need to do.

Ground balance on clean ground (you can sweep around in pin point mode to find a target less area) and then lock the ground balance. It will cut out a lot of extraneous sounds caused by the ground balance circuit as it tries to adjust for the changing ground matrix (including the junk).

You gave me the discrimination setting "first factory preset (just below nickle)." not the sensitivity. Your discrimination is fine where it's at, but if your sensitivity (gain) is also at the preset mark, it is likely too high for a junky area and you are picking up a lot of fringe signals from nearby junk targets. Bring the sensitivity (gain) down to around 6. This will cut down on picking up too many fringe targets.

Consider using a smaller coil under such conditions. The 4x6DD would be ideal or even the 6x9DD (my favorite).

I had also asked how the "ghost" targets pin pointed, broad or tight beeps, other nearby targets,...? Can you shed some light on this?

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Old 09-03-2008, 12:00 AM
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Quote:
Originally Posted by Rudy View Post
If the area is that trashy and littered with ferrous there are several things you need to do.

Ground balance on clean ground (you can sweep around in pin point mode to find a target less area) and then lock the ground balance. It will cut out a lot of extraneous sounds caused by the ground balance circuit as it tries to adjust for the changing ground matrix (including the junk).

You gave me the discrimination setting "first factory preset (just below nickle)." not the sensitivity. Your discrimination is fine where it's at, but if your sensitivity (gain) is also at the preset mark, it is likely too high for a junky area and you are picking up a lot of fringe signals from nearby junk targets. Bring the sensitivity (gain) down to around 6. This will cut down on picking up too many fringe targets.

Consider using a smaller coil under such conditions. The 4x6DD would be ideal or even the 6x9DD (my favorite).

I had also asked how the "ghost" targets pin pointed, broad or tight beeps, other nearby targets,...? Can you shed some light on this?
Rudy, I think you have nailed my problem,I went out this evening for about an hour just to trouble shoot and get to the bottom of this whole thing.My feeling is that I was running my gain way to high like you had mentioned in your previous post. When I ran the sensitivity on the factory preset I was losing that smooth clear continuous hum in the head phone and my audio and VDI alerts were eratic. As you guessed when I was running high my pinpoint sweeps were broad and not getting that good crisp audio alert when on a good target. Tonight I backed the sensitivity down to 6 and in some of the areas had to even take it down to 4 but the machine was very precise and sharp in finding and pinpointing targets. This one goes under the heading of getting to know my machine and I thankyou for helping me get there.
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  #8  
Old 09-03-2008, 12:24 AM
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Glad I was able to be of help.

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Old 09-07-2008, 04:18 AM
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Rudy, Thanks for the information. I have a DFX, and have had the same problem. It comes in as a variety of signals (dollar, dime, etc.), but often is a nice tight signal, coming from both directions when I do the cross pattern to pinpoint it. It often happens on our farm; there's a fair amount of trash, but not unreasonbly so. Last week I had a solid signal for a dollar, a few inches down. I went down 3 inches and hit a rock. Nothing on my pinpointer (Whites Bullseye) as I dug. Kept getting the dollar signal till I dug out the rock. Then nothing. At all. Anywhere. Hole was silent, the rock had no signal, the grass in the area was empty. Happens often enough to be pretty frustrating. This is all on factory settings. I usually rezero (ground) it if I suspect bad signals, but don't change the gain, etc. I have to get my manual out and play around with it some. This is why I love this forum. You guys are great! CT
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  #10  
Old 09-07-2008, 12:55 PM
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You may be running into Hot Rocks.
HOT ROCK: A rock that contains a higher or significantly different concentration of nonconductive ground minerals than the surrounding ground to which the detector is balanced. A metallic (positive/conductive) response will be heard in the motion and non-motion modes and a null or negative drop in threshold is heard in the All-Metal ground balanced mode over these rocks. Ironstone is a typical hot rock. VDI number response is +95.

I'm not a DFX expert, but you may want to read up on the HOT ROCK REJECT capabilities of your DFX.

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  #11  
Old 09-09-2008, 11:54 AM
Rocksann Rocksann is offline
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Default Application to ace 250?

Quote:
Originally Posted by Rudy View Post
If the area is that trashy and littered with ferrous there are several things you need to do.

Ground balance on clean ground (you can sweep around in pin point mode to find a target less area) and then lock the ground balance. It will cut out a lot of extraneous sounds caused by the ground balance circuit as it tries to adjust for the changing ground matrix (including the junk).

You gave me the discrimination setting "first factory preset (just below nickle)." not the sensitivity. Your discrimination is fine where it's at, but if your sensitivity (gain) is also at the preset mark, it is likely too high for a junky area and you are picking up a lot of fringe signals from nearby junk targets. Bring the sensitivity (gain) down to around 6. This will cut down on picking up too many fringe targets.

Consider using a smaller coil under such conditions. The 4x6DD would be ideal or even the 6x9DD (my favorite).

I had also asked how the "ghost" targets pin pointed, broad or tight beeps, other nearby targets,...? Can you shed some light on this?
Hi Rudy,

Would this apply to an ace 250 by reducing the sensitivity? I have had
problems with a broad signal but no object when digging. This was in a tot
lot with some ferrous and pop tops.
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  #12  
Old 09-09-2008, 06:20 PM
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Originally Posted by Rocksann View Post
Hi Rudy,

Would this apply to an ace 250 by reducing the sensitivity? I have had
problems with a broad signal but no object when digging. This was in a tot
lot with some ferrous and pop tops.
Yes, it would also apply to your ace 250. Quite often when the detector is acting erratically and is beeping when no targets are present, it is an indication that you are running it too hot. Back off on the sensitivity enough
to achieve stability.

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  #13  
Old 09-13-2008, 01:40 PM
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Thank you! This was my problem yesterday. Made me nuts. I've the Ace 250. Now I know why.
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  #14  
Old 09-13-2008, 02:23 PM
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Thank you! This was my problem yesterday. Made me nuts. I've the Ace 250. Now I know why.
You are welcome.

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