TGSL Tuning & troubleshooting

[Vladimir]

If the RX coil Shild not cover the GND, what the purpose of Shild?. The purpose is to electro-static voltage of green grass brought to GND. The second question is "trickle" of the signal. My experience is that the RX and TX signals must be separated with Shild. This will avoid interference in the cable.

[simonbaker]

Looking back through the threads now, I get the impression that Ivconic arrived at his conclusion through trial and error. It would be interesting to see how Tesoro does it, but we cannot compare a concentric directly with the DD design unless they offered one for the TGS.
Don

Oh yeah - every other moment I forget about concentric. But maybe from shielding standpoint it could be similar?

Also, I think the TGS was not that ambitious a detector and the designers probably didn't pull out all the stops for air depth -- they considered cost. For example, the current low-end Compadre cable does not have a shield that is grounded to the PCB -- in fact, with a magnifying glass, I cannot see any trace of a shield at all. There could be one that is grounded in the coil head, but maybe not. So we might have to check a high-end Tesoro to see what their cable shield philosophy is. I think many current MDs use high resistance shields for the coils, like graphite paint, etc., so very different design.

-SB

[simonbaker]

If the RX coil Shild not cover the GND, what the purpose of Shild?. The purpose is to electro-static voltage of green grass brought to GND.

Yes, but you could shield the RX coil and RX wires with a grounded shield without grounding one of the RX wires to the shield.

The second question is "trickle" of the signal. My experience is that the RX and TX signals must be separated with Shild. This will avoid interference in the cable.

I agree that seems to makes sense. But the two coils are somewhat coupled magnetically anyway (since the null signal is never zero). So the small coupling in the cable maybe is not significant. And any coupling is not "noise", it is a constant phase signal which is eliminated by the band-pass amplifiers.

-SB

[Vladimir]

Yes, but you could shield the RX coil and RX wires with a grounded shield without grounding one of the RX wires to the shield.

-SB

Yes, but what is happening with Shild of cable, and cable acts as an antenna?. It is this complex matter. the difference between good and poor detectors is usually in the shielding coil and cable.

I agree that seems to makes sense. But the two coils are somewhat coupled magnetically anyway (since the null signal is never zero). So the small coupling in the cable maybe is not significant. And any coupling is not "noise", it is a constant phase signal which is eliminated by the band-pass amplifiers.
-SB

With this I do not agree, I had to fix the situation Garrett CX 3 which was damaged Shild the cable, nothing could be done until the entire cable was replaced. Shield of cable in Garrett is Al foil and is especially in the Tx pair and Rx pair wire. Any damage to them causes great instability in the work.

Regards

[simonbaker]

Yes, but what is happening with Shild of cable, and cable acts as an antenna?. It is this complex matter. the difference between good and poor detectors is usually in the shielding coil and cable.




With this I do not agree, I had to fix the situation Garrett CX 3 which was damaged Shild the cable, nothing could be done until the entire cable was replaced. Shield of cable in Garrett is Al foil and is especially in the Tx pair and Rx pair wire. Any damage to them causes great instability in the work.

Regards

I agree with you. I'm giving some theoretical reasons why I could believe various different shield arrangements might or might not work. Actual experience is what matters; then try to figure out why it is the way it is. As I mentioned, the Compadre doesn't seem to use a shielded cable at all, and its circuit is probably similar to TGS.

It's good to go back and retry designs that maybe we thought didn't work -- its always possible a problem was due to something else. We'll see what dfbowers finds with his ungrounded RX coil.

To experiment, it would be very useful to make a good coil with a connector at the coil so we could quickly try different cables and cable groundings. Maybe that is what dfbowers is working on.

I am happy that Vladimir's cables work well for him because they are quite easy to obtain and work with. I have tried them also, but first I need to make sure my PCB and coil are very stable before carefully comparing cables.

Regards,

-SB

[Vladimir]

I would not want to create confusion, I recommend a cable that works nicely with modifications to the PCB that I made. With original design, I had very big problems in the wet grass. The laboratory is all nicely done but the soil was very unstable. Now I have these problems solved.
Simon, I accepted your proposal and resistors R25 and R26 was reduced to 100k, works very well with this change.
Regards

[dfbowers]

I noticed that wet vegetation does disturb the operation of the TGLS somewhat.. Dry land, not at all..


I have the same problem.
A wet sponge give the same problem,a lot of falses.
But when I acros the front of the coil with my forearm (ulna) it give a good response,like a coin.
Who can tell me, what the problem is.
Thanks.

Grt Nakky

That's behaving as though it's not shielded at all.

[simonbaker]

I would not want to create confusion, I recommend a cable that works nicely with modifications to the PCB that I made. With original design, I had very big problems in the wet grass. The laboratory is all nicely done but the soil was very unstable. Now I have these problems solved.
Simon, I accepted your proposal and resistors R25 and R26 was reduced to 100k, works very well with this change.
Regards

Your results are very useful and appreciated. It will help me with some similar ideas I plan to make for future PCBs.

Regards,

-SB

[simonbaker]

That's behaving as though it's not shielded at all.

I think a sensitive detector may very well detect a sponge and possibly a forearm. They certainly can go crazy on wet sand.

-SB

[simonbaker]

I think a sensitive detector may very well detect a sponge and possibly a forearm. They certainly can go crazy on wet sand.

-SB

Never mind, what am I saying? -- TGSL shouldn't detect a forearm, I'm pretty sure. First, take off your watch and rings . Are you using a finished coil cast in a form, or a loose coil on your workbench? Be really sure you aren't vibrating something, often I think I'm detecting something when actually I'm shaking the floor or table or the cable. Even making air move can affect loose coils. These things are like microphones until they are buried in epoxy.

If worse comes to worse, you can find forearms underground..... CSI will hire you...

Love that Euro, will be reporting on more testing soon.

-SB

[dfbowers]

I think a sensitive detector may very well detect a sponge and possibly a forearm. They certainly can go crazy on wet sand.

-SB

Yes, I could see that.. The shield should remove most of the undesirable effects though. Nakky, do you observe this at reduced sensitivity?

Don

[Vladimir]

Again I need to be in disagreement, the most sensitive detector can be stable if the Shild well done and all the nice set. Of course, I write about stability in the wet grass, sand or other substrates that are full of static charge. If the detector responds to static charge, make sure you have somewhere made a mistake in the construction. It also has the opinion that the Tx does not have to put Shild, wrong, peaks of the static charge will pass on the oscillator and thus again cause instability. In the laboratory all that there is not much sense, but on the ground, any instability or disorder in the work, cause a false signal, no response to a target or a lot of noise that make it impossible for the search. The result is: useless detector, which is good only for laboratory demonstration. In the process of constructing, for me there are always two cycles, laboratories and soil , if both cycles give good effects and it is a good detector.
Regards

[Vladimir]

Also, the sensitivity of the arm can warn of improperly configured GEB.

[Vladimir]

Most common mistakes in the construction of the detector (Part I):
* Badly pinched coils
* Rolled coil without glue
* Al foil broken
* Replaced the polarity of the coils
* Poor connected Shild
* Thermal stability of the coil is bad (hard charging polymers)
* Hydro protection is poor
* The cable has a bad performance (capacity, a small number of wires in Shild, poor choice of cable)
* Bad connector from the coil (an inexpensive, mechanically unstable, corrosive)
* PCB is not well connected to GND
* PCB is not cleaned of welding products (tinol)
* PCB is not protected by varnishing
* System error in setting the parameters
* Poor choice of detector box
* Poor or inadequate battery

[simonbaker]

Tuning/Troubleshooting Review

Reviewing recent conclusions regarding tuning/troubleshooting.

1. DC output level of LM308 / U104 chips may be important factor affecting sensitivity. Checking LM308 chips and replacing as needed might help sensitivity and depth. However, what is the best dc output level, and should both chips be the same? dfbowers mod allows more range in sensitivity threshold to compensate for off-spec dc output levels of chips. Someday we can experiment with separate threshold for Disc and GB channels.

2. Noise picked up by coil/cable may be important factor in limiting air test depth, especially if performed indoors where EMI is high. A good place to measure noise is at the output of LM308 / U104 chips. If the peak-to-peak noise is much above 20-25 mV it is probably a problem. It is important to test somewhere as noise-free as possible; not easy I find. I tested dfbowers nice TGSL in a local park recently and got terrible motorboating a few minutes after turning it on, but not at home. At home, I get different noise at different times of day and different days. I will drive into the mountains to test more. I believe noise reduces depth by breaking up target signal into pieces which are filtered out by the next low-pass filter.

3. I'm using dfbowers TGSL as benchmark to evaluate my own PCB and coils. I connect my coil to his PCB or his coil to my PCB. But it is not so easy to compare air tests as I thought. The quality of the signal causes confusion -- how much chatter is present, how long is the beep, how reliable is the beep at a particular depth, how fast do I sweep the coin, how does the loudness of the speaker/headphone affect my judgment, etc. Also, because of parts variations, the oscillator frequency is not identical and the RX resonant frequency not identical -- how do I adjust those for a good comparison.

My impression so far is that my PCB is close to dfbowers' in depth test, perhaps the beep is a little shorter or the depth just a little less. Many more tests needed though.

I do not have a good coil to compare (mine typically use much thicker wire and have too much gain), so my next step is to try to make some coils quite similar to dfbowers'. I have some 30 AWG wire that I'll use, and a modified coil-winder to compress-glue the coil as I wind. I am also working on a mold to cast a final coil out of resin -- not as good as dfbowers vacuum-formed shell, but hopefully solid.

dfbowers uses "Spar Varnish" to stick his coil windings together as he winds. I could not find smaller than a quart, too expensive, so I may try water-based polyurethane (because I have some). I know, water-based may be bad. If the coils stink, I try again with non-water-based polyurethane. I'd like to find something that is tough and permanent but not so nasty to breath.

This morning I was getting target detection probably at around 25 cm indoors with dfbowers' or my PCB connected to dfbowers' coil. But I would have to make a video so you could evaluate what that really means. Eventually I'll try to do that. As mentioned, a trip to the mountains is planned - but I know there are various transmitters in the mountains, and also that ELF (Extremely Low Frequency) transmissions, such as submarine communications, probably penetrate mountains easily. I feel like noise is a poltergeist haunting me right now.

So I'll build some coils, continue testing dfbowers TGSL in various environments, continue testing my PCB with dfbowers coil (trying some tuning capacitors in the oscillator and RX input). I'll also test dfbowers' mod to the sensitivity threshold and effects of different LM308 chips; then eventually try separate thresholds on DISC, GB channels. Also I should keep an eye on batteries in dfbowers' TGSL to make sure I'm not running them down and affecting the tests.

I hope others with problems in their TGSL are trying some of these tests too and will report.

-SB