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TDI Signal Chart
Posted by: Reg
Date: May 15, 2013 10:07AM
I have never seen a chart that tries to explain how signals change as the GB control is changed. Now, for the record have you ever given the thought as to how to do this that makes sense. Well, I did and it isn't easy but I hope once a person better understands this chart, the more sense it will make.

Once you better understand the chart the more it will make sense. For example, if you look at the ground signal line, you notice it crosses the 0 line at less than 9 on the chart. At this location, the ground signal is minimal so there is little to no ground response. As you move away from the crossover setting on the GB, you will notice the signal from the ground gets stronger. Move towards a lower GB number and the GB signal becomes a high tone. The strength of this tone increases as you move away from the balance or crossover point.

Move to the right or a higher GB number and this ground signal becomes a low tone. The farther to the right and the ground signal becomes stronger.

This same technique holds true for all signals from metal objects also. This means that if you set the GB low when looking for silver coins, the signal will be weaker than it would be if the GB was set at maximum.

So, in simple terms, any high tone will become higher and louder as the GB is moved to the left and any low tone will become lower and louder as the GB is moved to a higher number.

Let me know if this graph makes sense.

Reg



Edited 4 time(s). Last edit at 05/15/2013 10:19AM by Reg.




Re: TDI Signal Chart
Posted by: Reg
Date: May 15, 2013 10:23AM
One more thing I wanted to post separate from the previous post is why when the GB is off, all tones are high tones. Well, if you look at the chart I just posted, you will note that as you move the GB to the left, more and more items become high tones. Unfortunately, you run out of adjustment once the GB control is at minimum. Well, that isn't true really, because if you could adjust the GB to a minimum setting, then all signals would become high tones and that is exactly what happens when you turn the GB off. With the GB off, the GB is at minimum and thus all signals are high tones.

One more note, if you looked at the chart and did so right after I posted it, I did add more info as noted by the 4 times I edited the post. So, if you are one of the earliest readers you might want to look at the post again to see if what I added helps.

Reg



Edited 1 time(s). Last edit at 05/15/2013 10:26AM by Reg.

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Re: TDI Signal Chart
Posted by: LittleJohn
Date: May 15, 2013 11:53AM
The more I read your writings...the less intelligent I feel. Even when I read and re-read them over and over, I still feel like I am not getting the message that you are putting out there. I am trying to understand how the settings I used last night, translate based on the latest information you have put out in the past few posts you have done.

If I am even close to being partially correct, instead of relic hunting with the pulse delay at 10, I should have been at 25 and ground balanced accordingly. I even tried hunting in high conductor only...and still kept digging every nail or piece of rusted iron that went under the coil. Did I set myself up for failure by having the TDI set up this way, in that I would only be digging iron...and the lead bullets I was after became low conductors based on my GB or pulse delay...or both? Trying to wrap my head around this..thank you for your patience.

LittleJohn



Diggin' it up in South Central PA!

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Re: TDI Signal Chart
Posted by: LittleJohn
Date: May 15, 2013 12:07PM
Ok looking at and studying this graph is starting to make some sense....:stars: That's exactly what I did....



Diggin' it up in South Central PA!

Re: TDI Signal Chart
Posted by: filternozzle
Date: May 15, 2013 12:21PM
Reg, I think the graph is great, it really shows how it is.
Would it be possible to add in the a line or further graph to show the effect of pulse delay? That would complete the picture

Re: TDI Signal Chart
Posted by: Reg
Date: May 15, 2013 12:39PM
filternozzle,

It would be easier to simply test the ground signal yourself and see where it ground balances if you turn the delay up to something like 17.5usec and see what happens.

Now, I will say that all items don't move in tandem but vary somewhat, so experimenting is the best way to actually determine what is happening. So, trying to draw what happens could get more complex than it is worth which would add to further confusion.

Reg

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Re: TDI Signal Chart
Posted by: LittleJohn
Date: May 15, 2013 12:44PM
Reg is that what happened to me yesterday?



Diggin' it up in South Central PA!

Re: TDI Signal Chart
Posted by: Reg
Date: May 15, 2013 12:54PM
Little John,

You are looking for simple quick answers to your questions and, unfortunately, there aren't any. So, my recommendation is do what you are doing and listen to the signals from the various objects with the delay at 10 usec rather than begin changing the delay. Much can be learned from simply listening and playing with a target signal.

For example, lets say you get a strong low tone. You need to listen to see if that signal is a double blip or a single consistent tone. Next try moving around the target and check again. Does it ever change to a double blip? A double blip will tell you something and help you eliminate some trash without having to dig it once you have confidence in what you hear.

Besides, before you begin moving the delay, we need to do more experimenting with changing only the GB control. But even that shouldn't be done until you are quite comfortable with what might be under the coil without digging up the target to see. You may not know for sure just what the target is, but have a better idea simply by the tone of that target and how that target tone is heard.

It has taken me years to learn what I know so I am speaking from experience. Most people give up way and try shortcuts way before they learn the detector and miss out on the true value of the TDI. What is even worse is people are not willing to take the time to really learn what the TDI is telling them.

The only advantage of people with little to no patience buying the TDI and then selling it a couple weeks later is someone else usually gets a good deal.

It does take patience and practice to learn. A perfect example is a guy I know had a much more expensive PI and purchased a GS 5, which is the pre TDI and it took him a year before he realized the benefits of the GS 5. Before it was all over with, he was using the GS 5 most of the time, and the GS 5 didn't have the conductivity switch.

I mentioned the GS 5 because the initial TDI units were practically identical to the GS 5 in design. The TDI has evolved a little but is still based upon this initial design.

Reg

Re: TDI Signal Chart
Posted by: Reg
Date: May 15, 2013 01:00PM
Little John,

Don't feel bad about feeling less intelligent. I have been studying PI's for about 13 years now and when I communicate with Eric Foster who has been working with PI's for years and years, I feel much like you do. Eric has so much more knowledge than me it is embarrassing.

As I said, it takes time to learn the TDI. Please have patience and it will come. In the mean time, do most of your hunting at 10 usec until you have a good handle on just what a target might be.

Reg

Re: TDI Signal Chart
Posted by: filternozzle
Date: May 15, 2013 01:04PM
Quote
Reg
filternozzle,

It would be easier to simply test the ground signal yourself and see where it ground balances if you turn the delay up to something like 17.5usec and see what happens.
Now, I will say that all items don't move in tandem but vary somewhat, so experimenting is the best way to actually determine what is happening. So, trying to draw what happens could get more complex than it is worth which would add to further confusion.
Reg

That's ok Reg, I have been playing around and noticed that pulse delay does have an effect and can be quite useful. Thanks again for sharing your knowledge.

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Re: TDI Signal Chart
Posted by: LittleJohn
Date: May 15, 2013 02:53PM
I have no intentions of getting rid of this detector, and am probably the most patient person you may ever meet Reg. I am looking for answers, this much is true. I am in this for the long haul and will spend whatever time and practice is necessary to become efficient with this machine.

I have waited several years to be able to get one, and now that I finally have, I may be chomping at the bit so to speak...to get started with it. But the patience is definitely there, and I would hope that a process engineer by trade would be able to understand the theory and application of the rules and principles that surround these machines.

That being said I'll continue following your advice and moving forward with little steps as I go. Thanks again for your guidance and sharing your knowledge.

LittleJohn



Diggin' it up in South Central PA!

Re: TDI Signal Chart
Posted by: Reg
Date: May 15, 2013 03:33PM
There is a reason I recommend going slow and that is to learn signals from all possible targets so important items are not left behind. You will learn that some places the iron junk decays away faster than at others. So, simply reading someone elses suggestions may work but it is also a recipe for disaster. Leaving something behind and then noticing someone else coming along behind you and finds that something valuable cause people to quickly doubt their detector.

This doubting the detector isn't the detector's fault. Not knowing what to expect and having a detector appear to fail causes people to give up on a potentially great detector.

I am getting ahead of myself but as an example, lets say you want to hunt silver and older copper coins in a park. So, you follow a recommendation and automatically turn the GB back to something like 2 or 3. At this setting you may miss Indian heads or the signal from them is quite weak but that is ok. Lets also assume this particular park you visit is relatively free of ferrous junk. (Yes, they do exist). However, the only way to tell if a park is loaded with iron junk is to actually dig objects or at least check using reliable testing to see if much iron is present. If the park has little to almost no iron junk there is no need to turn the GB back and not turning it back increases the potential depth of detection of coins by several inches. In fact, then turning the GB to maximum can maximize depth on most copper and silver coins. Knowing this can mean the ability to detect some of those deeper coins or not.

So, there are particular reasons to dig a little trash once in a while.

Reg

Re: TDI Signal Chart
Posted by: nlhawk
Date: May 17, 2013 01:34PM
Reg,

LOVE THE GRAPH !

It took ten seconds for my eyes to adjust, then went from 0 to 60 in a flash. For me your graph makes perfect sense.

Thanks.

Lee

Re: TDI Signal Chart
Posted by: GoldChaser
Date: May 17, 2013 07:36PM
That's awesome, Reg! Thanks for the post. As they say, a picture is worth a thousand words.
So I guess larger silver or a quarter would be parallel to the "Indian Head" only perhaps slightly to its left?


Re: TDI Signal Chart
Posted by: Reg
Date: May 18, 2013 12:28AM
Copper pennies (with the exception of Indian Heads and zinc ones) and most US silver coins will normally still be low tones at minimal GB setting. Very small silver coins such as a half dime or very old Roman or other small old coins can vary with many being a high tone at minimum setting of the GB.

Gold objects vary all over the spectrum, with most gold nuggets remaining a high tone. Certain very pure gold nuggets may transition from a high tone to a low tone at about the 1/4 oz range. Nuggets having a very irregular surface and/or higher silver and/or copper content will have a tendency to remain high tones but this depends upon the actual gold chemistry. This is why it really helps to be able to test different size nuggets from a particular area to see just what setting may be the best.

So, in many locations one can set the detector to low conductor (high tone), set the GB at normal and hunt away. With this setting, in many places most of the gold will be detected while much to most of the thicker ferrous junk will be ignored.

Always try to test the type of gold in the area where you will be searching to avoid errors though.

Relic hunters should try to test desired targets when possible. There is no substitution for testing and learning the signals of what you will be hunting for. Simply taking someone Else's settings and using them can get you into trouble or cause you to miss good targets.

The discrimination feature of the TDI certainly isn't perfect but it does help.

Reg

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