TDI Pulsescan modifications AND BIG coils

[XLOOX]

Does anyone have experience with these super-sized coils on a TDI?

No personal experience with coils larger than 18" on TDI but if you are considering DIY coil building of any size then
https://www.geotech1.com/forums/forumwould def be in your must read resource list.

 

[AVXVA]

The problem with a silent threshhold is that deep targets (at the detector depth limits of the coil/machine), can register as a negative signal, where the threshhold volume dips rather than rises. If you are running your machine with a silent threshhold at the time, you will walk over these potentially great targets without having any inkling of their existence, even though your gear detected them.

Oh. My. God...

As a matter of coincidence, THAT VERY THING happened yesterday. The TDI was running well, threshold purring consistently, and then it went blank. I swept that spot several times--same thing--the sound stopped. Couldn't figure it out.

Today, I'm 80-miles away from it, and I don't think I remember where I was exactly...

I will not make that mistake again..

Rob

 

[AVXVA]

By the way, the ProScan TDI manual says (in several different places) that turning the GEB circuit ON reduces the absolute detection depth of the machine. Running the TDI with the GEB turned OFF is deeper.

Does anyone know how much deeper? 10% ~ 50% ~ "A lot" ~ "Not much" Anyone?

Thanks

 

[grubstake]

This linked article by Jonathan Porter for Minelab, comparing the 19" GPZ coil with the standard 14" when chasing maximum depth for big gold, includes an enlightening video wherein he demonstrates the differing effects of the two coil sizes on signal audibility (along with different machine settings which aren't relevant to the TDI):

GPZ 19 compared to GPZ 14 - Nugget Dig! - Treasure Talk

 

[nesral]

By the way, the ProScan TDI manual says (in several different places) that turning the GEB circuit ON reduces the absolute detection depth of the machine. Running the TDI with the GEB turned OFF is deeper.

Does anyone know how much deeper? 10% ~ 50% ~ "A lot" ~ "Not much" Anyone?

Thanks

The Pro Scan TDI Manual is correct

In places or ground where GEB is not required a depth increase is noticeable with GEB off.

A wet beach is such a place; excluding heavily Black Sand Beaches where GEB is definitely required.

TDI have GEB On/Off switch so it's easy to set/adjust. . . . . ATX do not.

 

[AVXVA]

Now I'm studying at three (3) different coil designs in three (3) different sizes.

1) The 22" CoilTek mono coil,
2) The 21" - 17" DeTech SEF coil,
3) The 32" DeTech concentric coil.

All are designed for the Minelab pulse inductors.

As you know, application is large meteorites in western Kansas at a depth of several feet to six (6) or seven (7) feet. The detector is a White's PulseScan TDI (pulse induction.) I don't necessarily need to pinpoint them, I just need to know something is there.

Which of these coils is consistently deepest?

The 32" concentric is impressive in transmission, but I'm thinking the small diameter return coil is maximized to target fist-sized or smaller targets.

My guess is the CoilTek mono coil is deepest. (And that is just a guess.)

Any experience, insight or advice would be greatly appreciated.

What in everyone's estimation works best (ground balances) with the TDI PulseScan?

Thank you.

Rob

 

[XLOOX]

From some of Reg Sniffs old posts on the TDI detectors, for coils over 20" he recommended using 15-20us delay and High mode.

Now that is for deep large gold ( max 2x coil diameter deep) so you would need to see if bigger deeper iron gave a reasonable signal in High or not.