Would like some help please on a specific coil for my TDI Pro,i have the option of buying this brand new Coiltek 6'' Mono coil which was of course specifically designed for the GPX range of detector,the GPX Mono coils do work very well on my TDI Pro as i own and use most of them on the TDI.
Has anyone specifically used this small 6'' Mono coil i am looking at using it most of the time because i am using smaller coils more and more due to the problems that i am hving with a broken wrist that i had from a bike accident decades ago,does anyone have any thoughts on this combination please.
By Steve Herschbach
My first comment regarding discrimination with a ground balancing PI like the TDI and others is that people may be expecting things of the TDI it cannot deliver, and may be better off with a good discriminating VLF detector. If your priority is discrimination, no PI will discriminate like a VLF.
There are two ways to tune the TDI. The first and preferred option is to tune the detector for the best depth. On low mineral beaches ground balance "off" usually give the best performance and you generally have to dig all targets. The sensitivity control and pulse delay are set to the desired level of quiet operation. You have to adjust those settings for your conditions. Forcing it by using settings other people use is fruitless. Salt conditions do vary as does mineralization and electrical interference, and the machines themselves vary by a small amount.
I notice many people think lower settings will cause lost depth and therefore insist on higher settings, and then complain the machine is unstable. It simply is what it is. Adjust the machine for the conditions. If it does not perform to your satisfaction, use a different detector. You can't make a detector do what it does not want to do.
As ground mineralization increases on some beaches, there is a point where using the ground balance “on” gives you more depth. Only with experiments can a person determine which setting gives more depth on your beach - ground balance “on” or ground balance “off”.
If you use the ground balance, it BY ACCIDENT creates two audio classes of targets, those above the ground balance setting and those below the ground balance setting. These give either a low tone or a high tone. The resulting two classes of targets have only a little to do with what they are made of, but are based instead on the rate at which eddy currents decay in the target after the transmit pulse shuts off. Size has as much to do with the audio results as composition, just like on a VLF. The pulse delay sets the minimum level for this eddy current cut off or rejection. See Understanding the PI Metal Detector by Reg Sniff.
With ground balance “on” you would normally, just like with ground balance “off”, adjust the sensitivity and pulse delay for whatever level produces quiet operation. I usually just put the coil underwater and pump it in the water, and first try lower sensitivity. If that does not remove noise I raise the pulse delay a little and try again. In general I am trying to keep the pulse delay as low as possible and sensitivity as high as possible. Eventually through trial and error I find a combination of sensitivity and pulse delay that eliminates audio results when pumping the coil in saltwater.
The ground balance setting is determined by whatever setting gives no audio results when moving the coil up and down over the beach or the bottom when underwater. If basalt cobbles are present they may also need to be included in the ground balance tuning procedure. In extreme cases you may have to lower the sensitivity and pulse delay even more to get a proper quiet ground balance.
Again, once you have tuned everything for best performance, you will have a pulse delay setting and ground balance setting that ACCIDENTALLY creates two classes of targets. The only way to see the result is to test various targets. In the U.S. our coins are much more conductive than many European coins and retain eddy currents better, and therefore generally give a low tone while most jewelry will give a high tone. Large ferrous will give a low tone and small ferrous a high tone. Very large rings may give a low tone as will most silver rings. In Europe and other places the tones may vary from what we see with U.S. coins.
After experimenting to find out what items give what tones, you have a simple decision. You can dig one tone only, or you can dig the other tone only, or you can dig all targets. The results will be what you have determined by your experiments and if digging only one tone or the other loses items you do not want to lose then you must dig all items. If that is not acceptable, your should be using a VLF detector instead.
Now, if you are willing to give up some depth, you can try to purposefully misadjust the ground balance control to move the tone division point. Doing so may switch some items from one tone to the other for a better result as regards discrimination. This however puts the detector out of proper ground balance. In mild ground you can do this easily but in highly mineralized ground the machine will now signal when moved over the beach or the bottom or past hot rocks. The depth is lost as you compensate for this by again reducing the sensitivity or increasing the pulse delay. Again it all is a matter of experimentation. If a desired item that is giving a "wrong" tone can be made to give the opposite tone by misadjusting the ground balance you may benefit from this in milder ground. It may be that the lost depth or audio side effects from being out of ground balance are not be worth it. You have to decide.
To sum up, VLF detectors offer the best discrimination but may not get enough depth on mineralized beaches. A PI detector can get more depth, but any discrimination is an accidental byproduct of the ground balance system employed and will not separate targets like a VLF. In general you dig everything with a PI but in some cases you can derive benefits by digging some tones and not others, but you will without a doubt miss some class of good targets by doing this. That is just the way it is.
The first ground balancing PI (GBPI) I used for beach detecting was the Garrett Infinium. Next was the TDI and then Garrett ATX. All three have similar tone results, but the TDI has the additional benefit of allowing you to manually set the tone break point via the ground balance setting. I have also used similar tonal separation using Minelab GBPI detectors. I go into more in-depth detail on another post referencing the new Fisher Impulse AQ where I reference all my notes on all these detectors so I am going to link there for further study. The Impulse is basically a refined version of what the TDI is doing, with the ground balance control used first and foremost as a discrimination control, and as with the TDI there will be performance trades depending on the settings employed. Understanding one will help you understand the other.
This is a very complex subject for those wanting a simple VLF type discrimination system in a PI detector. They are however two different things, and you have to read and think quite a bit about how a PI detector actually works to get your head around all this. Or at a minimum do lots of experimenting and learn by observation. I have tried my best to explain things, but there is no magic tuning or answers I can provide that will make these machines do what people seem to want them to do - act like a VLF. They are not. If they do not discriminate the way you want I have no settings that will make it happen other than what I have tried to explain already. This is kind of a summary and along with all the other posts is really about all I can offer or have to say on the subject. I hope it helps!
Fisher Impulse AQ Discrimination Explanation
Where Will The Holes Be In The Fisher Impulse System
White's TDI SL Owners Manual
White's TDI Beachhunter Owners Manual
White's TDI Pro Owners Guide
Steve's White's TDI Review
Well I decided the TDIBH was too much of a handful in the water so I decided to move it on to a new owner.
Hopefully I’ll not regret the decision but I got what I paid for it so can’t complain too much. One of Whites best for dry and wet sand hunting but never got much market penetration....I guess most want VLFs these days ?
Time to change my profile.......just five machines now 😳
As I mentioned some days ago, I was afraid to have a non waterproof control box after minor works on the coil's cable and the PCB inside.
The final result of this morning Is been: lot of unstable treshold drift since a few minutes inside the water(no way to calm down the treshold even with GB off).
Some minor short cause I can see the voltmeter crashed and fuc...d up...
After almost two hours of terrible noise and a few real signals, nothing to Say but a finally stable treshold without signals at all when targets were under or over the coil...
This means to me:the coil isn't working anymore...
Maybe the dumping resistor?
Maybe the lower resistance due to the cable shortening?
Nope....The gasket leakage and maybe the connector too.
I don't even have the time to dismantle again today..🤬🤬🤬🤬
Pissed as usual
I am still need to metal detecting and learning an original tdi. So lately I have been experimenting with the different controls and how they affect the machine.
I read some instructions that mentioned running the gain at the point that the threshold remained steady and did not waiver. This typically leaves me with a gain of 3 or 4. Does this sound right or am I missing something?
I've been experiencing lower yields due to sites being detected, by me for sure and there are also signs by others previously. SchoolofHardNox's success on a beach using the Minelab GPX 5000 reminded me to re-read Steve's treatise on using the (in his case original big box Pulsescan) TDI for coin detecting.
I just a few days ago stumbled upon a promising site where extra depth could be key. It's a schoolyard going back at least to 1955. Unfortunately as is the case in many of my public sites, it has a history of backfilling. From aerial photos I see than in the 50's it was grass/sod covered but in the early 60's they put down gravel. The person who told me about the site (a person who walked up to talk when he saw me hunting a nearby park) said he was a student there 45-50 years ago and at that time it was (again) grass/sod. I did a one hour survey hunt with the Minelab Equinox (11" coil) and encountered a couple inch thick gravel layer about 5" down. I did find one Wheatie below the gravel, but 7" is getting deep for my detector + soil mineralization combination so if coins remain from the 50's (pre- gravel layering) then I expect I will do better with extra depth (and that may even be required).
One thing I've found in my detecting of these older sites -- there are always nails present. So even if my TDI/SPP can deliver in the coin category it's going to be signalling on a lot of nails. One of the tricks Steve used was to set the conductivity switch to high conductors (low tones) but the TDI/SPP doesn't have that feature -- I will be hearing both high and low tones. This is a dual disadvantage -- extra tones to have to mentally tune out but also extra threshold noise since both parts of the signal spectrum will be contributing to that as compared to only half when the conductivity-low switch selection is made (on all TDI's except the SPP version).
Here are some specific concerns:
1) Am I fooling myself thinking I can get extra depth with the TDI/SPP, particularly when it comes at the expense of a noisier threshold?
2) Which coil(s) should I be using (choices I'm considering are 6"x8" Nugget Finder Sadie mono, 7"x14" NF mono, and 12" round White's 'Aussie' mono)?
3) Should I flag the promising targets but double check with the Eqx 800 (and if so, should I use the 11" or 12"x15" coil on the 800)? (Note, even if I choose this route I will likely at first dig, regardless of what the 800 says, just to get an idea of what is giving the signal and how deep the targets are.)
Any other advice (from anyone) is appreciated.