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TDI Ground Balance On Versus Ground Balance Off


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Carl on the Getech just posted air test distances.

13+" all metal, 1-2" less in GB.

I'm assuming this is with the stock 12" dual field coil and a nickel.

This is right in line with what I've saw with the exception of GB on doesn't reduce my depth.  I'll check again and confirm. 

 

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It would be a help if the testers posted the year their SL's were built, along with the battery voltage at the time of the test.

Jim

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My SL was manufactured in 2014.

Rechargeable battery pack was 11.62 v

Fresh set of alkaline batteries in the Alkaline battery pack 12.61v

I re-tested my SL this evening using the above battery packs and the 12" dual field coil.

I saw, absolutely no air test difference between ground balance on and ground balance off.

So, it would be obvious if I was hunting at the beach, to use the GB on feature over the pure PI function of GB off.  At least I'd have some control over the iron and still hear the gold. 

Now I'd like to see other SL users post test results.

Curious to see a date relationship to the depth reduction of ground balance on.

 

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  • 2 weeks later...
On ‎5‎/‎17‎/‎2019 at 10:05 PM, Mark Gillespie said:

My SL was manufactured in 2014.

Rechargeable battery pack was 11.62 v

Fresh set of alkaline batteries in the Alkaline battery pack 12.61v

I re-tested my SL this evening using the above battery packs and the 12" dual field coil.

I saw, absolutely no air test difference between ground balance on and ground balance off.

So, it would be obvious if I was hunting at the beach, to use the GB on feature over the pure PI function of GB off.  At least I'd have some control over the iron and still hear the gold. 

Now I'd like to see other SL users post test results.

Curious to see a date relationship to the depth reduction of ground balance on.

 

 

I guess I should start by making a few statements:

If driving along you come up to a stop light and its red, what will you do?
You stop, right?  Natural habit of good driving behavior.  It’s late at night and you get up to use the bathroom, the room is totally dark, you can’t see anything, and what will you do?  Turn on some kind of light so you don’t fall, right? 

Now, I’ve said all this to make a statement about using my PI machine.  Typically I charge my battery pack prior to leaving the house and off I go.  When I reach my hunt site, I power up the detector, set gain to about 8, make sure the ground balance is somewhere around 7 ½ to 8, set pulse delay to 10, set the conductive switch to all and away I go.  Now, when hunting with my TDI this is a natural procedure for me, to insure these settings are checked before starting my hunt. 

Now I must correct a statement I made in response to ground balance off verses ground balance on.

Quote: “I saw, absolutely no air test difference between ground balance on and ground balance off.”

This answer is both true and false but I failed to perform one adjustment when I performed my test. 

The following is actual test results of ground balance off verses ground balance on.  The results plainly indicate there is a huge depth reduction (-2”) when the ground balance is first turned on up to about GB 6 ½ with both the dime and quarter but not with a nickel. At GB setting >= 6 ½ depth (air test is equal to or exceeds the GB off settings.  I must admit I was not adjusting the GB to these lower numbers when I made the above statement and I greatly want to apologize for the oversight.

Key note on the graphs:

Test were done with a battery voltage of 11.5 as noted on each graph.

GB Value 0 = Ground Balance Off

GB Value 1 = Ground Balance Minimum

 

 

 

 

 

USGA1007.pdf

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Finally, I think you have brought clarity to this issue Mark. It is not just ground balance on or off.... but where the ground balance is set in relation to the target type. Your tests confirm exactly what I would expect. At some ground balance settings there is no difference of import, and at other settings a massive difference. Excellent work and thank you very much. I guess it now falls back on others to compare and confirm.

I do feel like "duh, I should have seen that"! :smile:

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6 minutes ago, Steve Herschbach said:

Finally, I think you have brought clarity to this issue Mark. It is not just ground balance on or off.... but where the ground balance is set in relation to the target type. Your tests confirm exactly what I would expect. At some ground balance settings there is no difference of import, and at other settings a massive difference. Excellent work and thank you very much. I guess it now falls back on others to compare and confirm.

I do feel like "duh, I should have seen that"! :smile:

To be honest I'm kind of ashamed I had not remembered that.  I knew better but for some odd reason it didn't click when I tested the first time.

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Seriously, if somebody invented a ground balance system that had zero downside it would be a near miracle. It is just a fact that with electromagnetics and conductivity that certain ground signals and certain salt signals overlap with some good target categories. It's like the people who want to detect small gold in saltwater. It seems impossible to get people to understand that using conductivity as your basis it is impossible to separate out certain salt and gold signals. It is the same signal as far as the detector is concerned, and eliminating one also eliminates the other. Eliminating the ground signal is the same thing - targets that have any overlap with the ground signal MUST be reduced along with the ground signal. That is why inherently I flat out know that engaging a ground balance is a filter and there is always, always a cost to that on some targets in some locations. The key as Mark has remind all of us is it depends on the setting and the target, and most targets thankfully are not an issue if you are a coin and relic hunter. It's us gold guys that run into this almost daily.

The best way to plug these holes is multichannel/multifrequency comparative methods, which is something TDI lacks. There can be great benefit in learning where the "traveling hole" is and how it affects certain targets, because in most ground the TDI is very forgiving of a ground balance offset. In other words, for certain targets you want to purposefully move the ground balance setting away from the target response to get the best depth.

Really a great post Mark - I needed that reminder.

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Yup...that explains a lot, Mark...many thanks! If I can find the time, I'm going to have to rerun some tests to specifically target the GB settings, and see what's going on.

JIm

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5 hours ago, Steve Herschbach said:

 There can be great benefit in learning where the "traveling hole" is and how it affects certain targets, because in most ground the TDI is very forgiving of a ground balance offset. In other words, for certain targets you want to purposefully move the ground balance setting away from the target response to get the best depth.

 

This is a matter that I have been considering since the announcement of the Manta.  With the various Eric Foster variants there has not been a free lunch with this issue  So is there still a traveling hole or other gotcha with the Manta.  Is it simply a warmed over Foster design which accomplishes an improvement to certain targets but has unknown weaknesses?  The amount of time that is being spent to bring it to market points to some technical issues that are turning out to be difficult to resolve.

Likewise as you stated Saltwater is essentially liquid metal like mercury but not quite as conductive.?  So you can GB it out which is essentially just a discrim filter for the ground.  But get down into the 5us-7us territory and conductivity response of small conductors gets lost in the salt fog.

 

 

 

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Foster designs are single channel. My understanding is Manta is dual channel though I could be wrong - hard to confirm tech details right now for obvious reasons. I can easily imagine how they are working two ground balance points against each other to define a certain target range. It's a highly specialized unit, perhaps one of the most specialized ever made. But that's a whole nother story and different forum than this one.

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