TDI Beach Hunter Has Landed..... Question Time !

[Tony]

My TDIBH got here door to door from the USA in 6 days which is great....thanks again to Gerry at Gerry's Detector's !

I did some basic tests on my back lawn (which is devoid of any metallic targets to at least a metre).

I did notice that no GB was needed which is what I would expect but interestingly if the GB was left at "4", the detector would barely detect my gold ring. As soon as the GB was turned higher or lower, then the ring was detected at great distance. I know I can run with no GB (straight PI) but the depth was slightly improved with GB engaged.

I am wondering that when I hit the beaches, which down here are generally mineral/black sand free, where should I leave the GB if it's not required?

I will most likely bury a target and dial in the GB (assuming it's not actually needed for a proper GB) which gives the best response but I am very wary of a setting that might not see the target !

I am new to the TDI SL platform so any tips is much appreciated.

Thanks,

Tony

[tboykin]

Hey Tony. The TDI's pulse delay and ground balance controls work together. On certain targets in certain ground you might find that a perfect ground balance setting diminishes the target response. This is due to the fact that at that particular setting, the ground balance point effects the machine's sensitivity to that particular target. Some people call this a "P.I. hole" or "ground balance hole."

It's good to do ground testing to find out what effect it has on targets with different ground settings. One thing you can do when a target falls into the "ground balance hole" is adjust the ground balance slightly higher or lower to increase the sensitivity of the machine, or adjust the pulse delay to hit harder on that particular target.

[Steve Herschbach]

The short story is that ground balance is a form of discrimination that discriminates out the ground signal at any particular setting. The issue is that there is some overlap between the ground signal and certain desirable (or undesirable) targets. An accidental side effect of this is that the ground balance setting and pulse delay setting do determine whether the detector makes a low tone or a high tone. All targets over a certain setting make a high tone, and all other targets under that setting make a low tone. The conductivity switch suppresses one or the other of these tones, creating a simple discrimination system.

However, right at the setting itself the detector wants to make neither a low tone or a high tone - it is balanced! The signal right at the ground balance point is simply eliminated, and certain targets can get very weak or disappear if the setting overlaps how they respond. People use this to create discrimination schemes by purposefully mis-adjusting the controls.

How TDI Settings & Tones Interact

White's TDI Coin Settings

 

[Tony]

Tom and Steve.......appreciate the feedback which all makes sense to me.

Maybe it is more prudent to run as a straight PI (GB off) if no GB is actually needed.

Some more experimenting is needed but at least I know what the issue is.

Thanks again,

Tony

[Tony]

Okay, back from the beach and did some basic tests....

Nice clean white sandy beach so it would GB "the same" across the whole pot setting. No GB needed but a noticeable depth increase when GB engaged.

Now, the GB "hole" changes when testing a gold and platinum ring so I really don't know where to set the GB to maximise coverage and limit the "hole"....and then with the pulse delay skewing results even further.

Am I reading into this too much..................seriously thinking of keeping GB off unless it is really needed for those rare black sand spots.

Hmmmmmmmmmmmmmmmmm.........?

[Tony]

I have discovered that 4 x 18650 cells cannot fit into the battery compartment without Dremmeling that area and that is something I won't do. The battery compartment has 4 or 5 internal ribs that run down the whole length and this is what prevents those batteries from fitting.

It looks like it has to be a maximum of 3 x 18650 cells which of course won't get us to the fabled higher voltage and better depth of detection..........anyone know what a realistic depth increase would be from that extra 3.7v cell?

Thanks,

Tony

[Steve Herschbach]

I run the ground balance off unless the ground requires it.

TDI Air Test & Battery Notes

TDI SL Battery Pack Up Grade

Batteries And The TDI SL

[Tony]

Thanks Steve for those links.......I try to avoid creating new threads without duplication !

[Steve Herschbach]

Over at Findmall...

Simple DIY 16V Li-Ion pack for TDI SL

Do note that I do not vouch for or recommend aftermarket modifications. People are on their own with this stuff.

[GB_Amateur]

I commend XLOOX for giving objective details of his tests.  It seems he is displaying the tradeoff between run time and sensitivity.  His Li-ion solution provides an average of 15V (and its associated higher sensitivity) for 2.7 hours of runtime.  That is compared to Eneloop Pro NiMH at average 10 V for 6 hr and White's NiMH pack, also average 10 V but 4.5 hr runtime.

Users must decide if they want longer run time or higher senstivity.  You get both if you carry extra battery packs (==> extra weight and cost).  I doubt any of this is new qualitatively, but I appreciate XLOOX for putting quantitative measurements on these concepts.