Odd pinpointing quirk

[PSS1963]

I've had something weird happen to me with my MXT. I was hunting very junky ground - each sweep of the coil sounded like Morse Code! Sometimes I get a good target hit - nice high tone - and after making a few passes over the target from a couple different directions to be sure of the location I lift the coil, squeeze in the trigger, and lower it back to the target spot to pin-point, and I get . . . nothing, nada, not a peep, crickets! When this happens the visual display reads 12" which I think is the max the MXT recognizes. I haven't finished reading Jeff Foster's book on the MXT yet, but I've seen in the part I have read, a couple possible explanations for this. 1) it could be a GB problem (I generally work in "lock") . . . apparently, iron can make the all-metal threshold blank out (salt causes a dramatic increase) -or- 2) maybe I'm trying to PP in one of the coil's "dead spots" which he claims exist in every coil type and prevent detection at a certain depth and location relative to the coil center. This has happened to me using both the 9" spider and the 5.3" eclipse so maybe it isn't coil dependent.

My settings: C&J, 7-tone, Disc 0, Gain 10, light threshold hum.

Big mystery and a huge annoyance for me - I hope somebody has an answer.

-pete

 

[Flintstone]

Hi 1963, I have never had that trouble but I always just move off to the right of target and pull trigger. I don.t lift the coil, you might be losing ground balance if lifting to high. Try and just move off the target a little and pull trigger. That might help. Good luck

 

[PSS1963]

Hi 1963, I have never had that trouble but I always just move off to the right of target and pull trigger. I don.t lift the coil, you might be losing ground balance if lifting to high. Try and just move off the target a little and pull trigger. That might help. Good luck

Thanks for the input but I have to ask . . . doesn't being in "lock" prevent losing GB? Also, pulling off to the side doesn't guarantee me clean ground. A lot of the places I hunt have more than one target per square foot of area - its literally a sea of junk!

-pete

 

[Flintstone]

Even in lock it still tracks the ground. It will change if in pin point, I think, so if you lift the coil and pull pinpoint it will lose ground. Maybe some else that's know more will post, but I have been using a MXT for 14 years and I think that is how it works. Good luck, maybe both of us can learn something.

 

[Nancy-IL]

Are your batteries low? Mine chatters like "Morse Code" when it's 10 volts or below .

 

[PSS1963]

Are your batteries low? Mine chatters like "Morse Code" when it's 10 volts or below .

Thanks, Nancy. Just coming up on 25 hrs on the batteries and I still have a good 10v remaining and I've seen this behavior since day one. When I said a sweep sounds like Morse Code, this is how many targets (mostly nails) are actually in the ground - its not just chatter or falsing. Where I'm running 0 disc and 7-tone I'm hearing every one of them. The curious thing isn't the noise but the occasional lack of any sound when I try to pinpoint . . . its like saying you just got a solid motion hit on a target with a respectable VDI, made a rough pinpoint by "X"ing it and then all-metal (i.e. pinpoint) couldn't see it all!

-pete

 

[Aarong81]

When you pinpoint with the trigger, otherwise known as 'all metal mode', the ground balance has nothing to do with it. However, as you(Pete) mentioned...."pulling off to the side doesn't guarantee me clean ground." you know that when you squeeze the trigger that the pinpoint steps up and notches everything at and below the current detection of all metal by the coil. If it is over the target when you squeeze the trigger it will zero out the sensitivity of the coil relative to the target being detected. You know this already but it is part of the problem.

The other part of the problem that I highly suspect is that the 'good signal' that you are hearing is negative hot rocks(technically COLD rocks), Negative hot rocks are usually magnetite or contain magnetite. There are two types of hot rocks, negative and positive. Positive hot rocks are usually iron-bearing rocks. If there is ever a cure for hot rocks many more areas will be opened up to detect.

One way to tell if you are dealing with hot rocks is by setting your threshold where you can hear it and just as you are swinging over the suspect target the threshold goes completly SILENT just before and after the signal response. This 'silence' is the detector discriminating and cutting the audio. The good signal is secondary, which is the detector giving two different signals. Only one is correct, the one you 'don't' hear. A legitmate 'good target' does not cause the threshold to disappear before/after the signal. There are ways to detect in hotrocks but I have had very little success with only a couple silver finds in such areas. It's.....almost not worth it, but to each their own misery, erm, I mean journey.

The morse code behaviour and the inability to pinpoint both sound like hotrocks to me.

 

[Nancy-IL]

Just a thought....Have you tried to turn your discrimination up a bit. I run mine around 3 for all targets. Just a thought.

 

[PSS1963]

Just a thought....Have you tried to turn your discrimination up a bit. I run mine around 3 for all targets. Just a thought.

Nancy,

I've been running the Disc at 0 because I could use 7-tone and hear the 70's and 80's signals that I wanted to cherry pick without any nulling out from things that were below the disc. setting. This past Sunday, though, something happened in a park I was hunting that caused me to want to try a different strategy - at that site at anyway.

I had a complicated cluster of low and mid range targets in which I thought there was an intermittant high tone, but I was so boxed in by the junk (even using the 5.3 eclipse) that I wasn't able to separate enough to get a clean shot on it. The hunt so far had been very unproductive . . . a few dimes and pennies but no quarters or silver - not even a wheat. Clearly this park had been hit pretty hard by lots of people in order for me to not even be able to get a shallow quarter in two hours of hunting. So I decided to try and deconstruct the cluster a bit by picking off some of the signals around the edges where I could get a clean pinpoint - forget the middle - there the targets all averaged together and there was no way tell where one left off and the next began. I selected one on the periphery with numbers in the 60's figuring maybe I could at least maybe bag a zincoln or an indian - the machine said 3 inches. I plugged it and pulled out a lovely piece of aluminum trash, all bent and broken looking. Its condition suggested I might have torn it with the digging tool and there might be another piece of it still in the hole. My pinpointer throbbed a bit at the bottom center of the hole but it didn't buzz like when a target is very close - it was more like one to two more inches directly below where the first piece had been. Dug a little more and up came a gorgeous '41 Merc in EF to AU condition!
Sorry, no pic yet. The camera in my phone doesn't do macro.

I wonder how long that lowly piece of trash had stood guard over that dime and how much longer it would have if I hadn't decided to break protocol and dig something that was more likley to be junk than anything decent. Next time I go back there I'm going to try relic 1-tone and use some discrimination to block out the really low end stuff then just busy myself with digging the junk and see what turns up. Maybe I'll regret it, after an hour or so, but we'll see.

I'll let you know if I see the pinpointing issue while I'm running with discrimination - I'm curious myself.

Aaron - the soil I've been hunting has mostly been the dark sandy loam used for lawns and parks. Does that normally harbor hot/cold rocks? Also, if I raise my coil waist high before squeezing in the trigger, is it still going to zero out the sensitivity? (but if I lift less than a foot off the target it might?)

- pete

 

[Nancy-IL]

I understand now. Hmm. I always use relic mode when hunting for deep targets. Congratulations on the silver dime. I've noticed if there's so much as a little constant beep in the silver range, it's always a dig. Years back there were multiple targets but it was masked by an old roller-skate wheel. Turned out to be 5 silver coins surrounding the area. Sometimes you have to dig the junk to get to the good items.

 

[Wheat Cent]

My grad father's mxt does same thing and the pinpointing is extremely inaccurate my cz will say 5 inches mxt says like 8 it ends up being 5 and the location is usually off as well the mxt is good at finding targets but not giving you a good location to cut a plug. It also haa lots of trouble in areas with iron you need a double d coil to get past the junk and iron.