Am I Or You Costing Ourselves Coins By How We Pin Point?

[Critterhunter]

This has been bothering me for a while and I want to get some opinions on it. With the DD coils I've used on the Explorer or GT I could never quite master doing the standard method of pinpointing that most use. That would be using the very center of the coil to X off the target's location from two different directions. I never really gave that method much time or practice to get good at it, and I will if things are happening that I suspect might be.

My normal routine for the stock 10" coil is to use the heel of the coil to pinpoint the target in either discriminate or PP mode. I'll then move 90 degrees and do the same thing again to pin down the location of it. Using the heel of this coil seems to work better than the tip for me, and it's also the easiest way to PP in the water because I can then stick my big toe up against the trailing edge of the coil and use that as a guide for my scoop as to where to scoop.

For the 15x12 coil when I owned one on land I prefered to use the tip of the coil and the base of the "V" to mark targets with. However, in the water I would use the heel and base of the "V" for the above stated reasons I do with the stock 10" Tornado in water.

With the 12x10 I also prefer to use the tip of the coil/base of the "V" to mark targets on land, although the trailing edge/base of the "V" seems as good as well. I'm sure in the water I'll prefer using the trailing edge as I did with my other coils when water hunting for ease in guiding the scoop to the right spot.

Anyway, I have noticed with some very deep coins (usually wheats) that when I use the tip of the 12x10 to locate the target can seem to be in two different spots when checking from 90 degrees. Doesn't matter if I PP in discriminate mode or PP mode, that can often look to be two different locations when checking 90 degrees away on the target. The distance between the two spots can be as much as about 3 inches. When this happens I center in on a spot halfway between the two and dig there usualy with good results.

I've also noticed that some real deep coins can sound good and ID well from two directions using the center of the coil, but when I go to PP it's either what happens above or I can't even seem to get any idea of exactly where it might be. Again, doesn't matter if they are PP'd in PP mode or discriminate mode. Mostly I prefer using discriminate mode to center in on targets because it offers less chance for some other object nearby to throw off my centering. PP mode might sound off so something like a nail nearby while discriminate will only give a good ID when I'm just at the edge of the target with the edge of the coil/base of the "V".

As a result from the above I've passed up a few seemingly good coin signals because I just can't get any clue as to where the target was by using the edge of the coil. That started bothering me in that I might be walking right over some good coins, so I decided to do some air tests to see a few things. End result is that if I move the coil from far away and slowly approach the coin (in an air test) until I just do get a good coin ID out of it using the center of the coil...That if I keep that same distance from the coil and then see if the very tip or tail of the coil will also pull a coin ID from it, I'm finding that at the outer extreme edge like this the tip or tail will NOT give a coin ID. Remember that I've only moved the coil just close enough to where it just starts to give a good ID using the center of the coil to sweep over it.

That tells me a few things...That at the very outer fringe of detection depth a DD coil can act somewhat like a concentric in that the very center is going to be the very deepest. The difference between depth might only be 1/4th of an inch or so but we all know that can mean all the difference in detecting a deep coin or not. So I would overlap my swings as much as possible just like I was using a concentric. Sure, the DD has more uniform depth acrossed it's entire length than a concentric, but the fact remains that it seems to have it's very best depth dead center.

Coming full circle, my concern is that I might be detecting a good coin with the center of the coil but by using the edge of the coil to PP it I might be losing the target and walking away from it. My normal routine once I've used the center to discover a deep coin is to stay in discriminate and then check it from 90 degrees both ways using the edge of the coil. If I can't pull a coin ID I might walk away. I don't like the difference in depth from center to edge and so that tells me that I might need to practice and learn using the center of the coil to PP targets because I'm missing those real deep ones at the outer fringes of depth. I would think that using PP mode might even things up, because then I'm just looking for a sound off of any type to center on using the edge, but what bothers me about that is that I have found deep coins that I can hear in discriminate but PP mode will not sound off to.

To eliminate my fears it looks like I need to practice the center coil PPing method. Sure, I've read the technique in the past but am wondering if anybody has any pointers that you don't usually hear. Also, have you found the same thing for yourself- that the edge of the coil won't hear the coin or at least well, while the center gives a rock solid ID?

 

[erikk]

Well depending on which machine I am using and in or out of the water I don't vary too much on how I get the target. In the water with the Excal WOT I have dug so may targets that I don't even think about it. Get the signal, move the coil and go for it with my big scoop. In the dirt with either the Explorer or the F-75 if I get even a flash of a good number/tone I will dig it. If I get a signal from one way I will dig it. I guess what I am saying is if it beeps I dig. Don't get too wrapped up in technicalities and never walk away from a target unless you are SURE IT IS A 55gal drum (empty)

 

[fir469]

The one instance I noticed what you were saying about the SEF being just a tad deeper in the center was at the beach this past weekend. I located 4 targets that were just a threshold rise, no tone just raise in the threshold but a solid rise from 360 degrees. They could only be picked up with the center of the coil, they were too weak and deep for the edges to pick up. Pinpoint was very very weak also. All 4 targets were coins... 2 dimes, 1 penny, and a quarter. Dimes and penny were four solid scoops down and quarter was almost 5. Didn't measure but I'd say without exaggerating that they were about 14-15" on the dimes and penny and about 16 on the quarter. Unmistakable rise in threshold though, no nulling. Makes me wonder what I've passed in the woods now lol. Was sure an eye opener to the depth these machines are capable of. But case in point, I got no signal from the outskirts of the coil and only a faint whisper rise in threshold dead center of the coil, pinpoint was only clear in the dead center of the coil and was very weak. Once I took the first scoop the signal was lost on all of them but I kept going knowing something had to be there.

 

[Critterhunter]

Good info. That's what bothers me too. I need to learn to PP using the center of the coil because like I said it seems real deep ones end up in two places when I use the tip or I can't PP them at all. That bothers me because some of these were good coin signals for the most part, but since I couldn't finger them using the edge of the coil to PP I figured they must be spikes or something.

 

[synthnut]

fir469,
What you are experiencing in the rise in threshold is what a lot of beach hunters experience when there are few and far between targets on the beach .....THIS is where the setup with the audio amp to bring those whisper tones to light comes in .....Some like myself , who does not have as good hearing as you do , REALLY benefit from the audio amp ....It's set so that you amplify those whisper tones with the threshold set as low as possible and you raise the volume of the amp , then lower the threshold some more and raise the amp even higher ....You go back and forth until you threshold is set as low as it can go with the volume of the amp turned up as high as it will go and still be able to just hear the threshold .....When going over extremely deep targets , all you will hear is a change in threshold ....There will be no tone , and if you have a meter , surely no ID .... Bring a good shovel !!.....HOWEVER , if you are in an area that it populated by quite a bit of trash , this method will rip your head off with LOUD targets ....BE CAREFUL where you use it .. Jim

I learned this method from Oldbeachnut on the Beach/Water forum ..... There are not a lot of places I can use it by me because of the trash that's littered all over and under the beaches in my area .... I'd have to get rid of at least 4 ft of sand to get down to where there is any use for this ....Down on the NJ shore is a GREAT place to try this out ....There are beaches down there that get sanded in , and can utilize this technology to the hilt ......JIm


Critter ,
There is something about the physics of how a DD coil hears and locates targets .....but I can tell you that with the AT Pro , if you hit most of your round targets , the AT Pro seems to ID them as coins ......Some targets you can clearly distinguish a crown cap from the low/ hi/ low tone that the machine makes .....Sometimes though , the target sounds clearly "high tone " and you think it's a coin .......If you then check the target by slowly hitting it wth the heel , or the toe of the coil , and move slowly , you will get that low / hi /low tone that you DON'T get when sweeping and crossing the target in the middle .... Since the middle of the DD coil acts more like a Concentric coil , perhaps you are getting a more accurate pin point by using pinpoint mode ? ..... Another thing to consider is maybe there is another target in the area that is throwing you off ..... ?????......These are all just guesses ..... Jim