Biggest Coil On TDI SL/BeachHunter On Beaches?

[Roger]

What is your largest coil for gold jewellery on beaches?  What are your settings and why; mineralization of beach and ground balance settings etc?

On a beach when you try to ground balance and there is no change of tone through the whole turn of pot', with a TDI SL or BeachHunter, where do you set the GB? 

Bearing in mind, that received wisdom says that TDI SL/HeadHunter is deeper when in GB on. 

So far, a Detech 18"x12" Mono is deepest in my South Wales beaches in UK.

I'm including the BeachHunter as I know that some have modified them to plug in other search coils. 

 

 

[Geotech]

On 12/2/2024 at 1:08 PM, Roger said:

On a beach when you try to ground balance and there is no change of tone through the whole turn of pot', with a TDI SL or BeachHunter, where do you set the GB? 

Bearing in mind, that received wisdom says that TDI SL/HeadHunter is deeper when in GB on.

TDI is always deeper with GB turned off. Back when I did more beach hunting, the 12"DF coil was all I used, as it was the biggest available. I built 18" & 24" coils for cache hunting but never waterproofed them.

 

[Roger]

I beg to differ Carl as It is well noted that the Pulse Scan/Pro TDIs are deeper when used PI mode, but with the TDI SL and BeachHunter the opposite is true; deeper in GB mode.

"After doing side by side tests between the TDI Pro and the TDI SL I found that turning the GB off on the pro adds depth but by turning the GB off on the SL actually takes away depth," from 18th post:

http://www.dankowskidetectors.com/discussions/read.php?2,119233,119278

"The "deeper with GB on" is true with the SL, but apparently not the others.  Auminesweeper is right, and my tests also bore it out. Regardless of the GB setting, as long as it's "on" the air tests show a definite improvement. Reg S. and I discussed this at length, and didn't come to any conclusions as to why, though Reg mentioned the GB circuit on the SL is different than the other TDI's." ,from 3rd post by Jim in Idaho:

https://www.detectorprospector.com/topic/10023-tdi-ground-balance-on-versus-ground-balance-off/

There are several other references to the SL behaving differently to the other TDIs.

[Steve Herschbach]

18 hours ago, Roger said:

I beg to differ Carl as It is well noted that the Pulse Scan/Pro TDIs are deeper when used PI mode, but with the TDI SL and BeachHunter the opposite is true; deeper in GB mode.

"After doing side by side tests between the TDI Pro and the TDI SL I found that turning the GB off on the pro adds depth but by turning the GB off on the SL actually takes away depth," from 18th post:

http://www.dankowskidetectors.com/discussions/read.php?2,119233,119278

"The "deeper with GB on" is true with the SL, but apparently not the others.  Auminesweeper is right, and my tests also bore it out. Regardless of the GB setting, as long as it's "on" the air tests show a definite improvement. Reg S. and I discussed this at length, and didn't come to any conclusions as to why, though Reg mentioned the GB circuit on the SL is different than the other TDI's." ,from 3rd post by Jim in Idaho:

https://www.detectorprospector.com/topic/10023-tdi-ground-balance-on-versus-ground-balance-off/

There are several other references to the SL behaving differently to the other TDIs.

And I beg to differ with your differ. The “received wisdom” is incorrect in real world operation and is based on a lack of knowledge about the subtractive nature of the ground balance methodology employed. The ground balance is a subset of the full ground balance off signal where a portion of the signal is filtered or removed. By definition ground balance on can only add depth in relation to the ground conditions encountered. If a TDI was exhibiting better depth across the board with ground balance on versus ground balance off, my first thought is that something about the machine is defective.

The real world fact is it depends on the ground conditions and the desired target, and so depending on what you are doing will determine whether ground balance on or off will get the best results. In general if detecting for gold nuggets in hot rock infested ground, ground balance on will generally be your best choice. And in general, on most beaches lacking hot rocks ground balance off will deliver more the best results. Watch the video attached to Carl’s post… it’s spot on.

Seriously, what would Carl know, him being the designer of the TDI SL and all? 

The switch exists for a reason. If one setting or the other was absolutely better under all circumstances there would be no need for the switch. Don’t forget the TDI also has one of the largest detecting “holes” I’ve ever experienced with any detector. You can lose up to half the depth or more on targets that fall into or come close to the ground balance setting. Ground balance on will kill a certain range of targets depending on where it gets set.

 

[Roger]

Ah Steve, I see now; the received wisdom I have read is incorrect.  Thanks for clarification.  I'm just wondering why this received wisdom has not been challenged elsewhere in detecting forums?  Just goes to show one mustn't believe everything one reads on the internet.

Thank you Carl and Steve.

[Steve Herschbach]

1 hour ago, Roger said:

Ah Steve, I see now; the received wisdom I have read is incorrect.  Thanks for clarification.  I'm just wondering why this received wisdom has not been challenged elsewhere in detecting forums?  Just goes to show one mustn't believe everything one reads on the internet.

Thank you Carl and Steve.

The internet has become a lot like metal detecting.... have to sift though a lot of junk to find a few good things. 

[Geotech]

10 hours ago, Roger said:

I'm just wondering why this received wisdom has not been challenged elsewhere in detecting forums?

Usually when I see something I think is wrong I speak up, but I missed those posts. The SL GB method is exactly the same as the Goldscan & TDI. It subtracts a late sample from an early sample so there is really no way it can go deeper with GB on. It makes more of a difference with high conductors than low conductors but I just ran my SL and with GB off both a nickel & a quarter are about an inch deeper. And, as Steve points out, somewhere there is a conductor that is entirely notched out with GB on.

In any case, I have no idea what those guys were experiencing. Normally they know what the heck they are doing so it's a curiosity.