TGSL Tuning & troubleshooting

[Vladimir]

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

[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

[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

[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

[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 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

[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.

[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

[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]

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]

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

[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

[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.

[Vladimir]

Hi Vladimir:

I think what dfbowers was asking is: do you also ground the cable shields together at the PCB? (see green line in attached photo).

-SB

-YES- they are at GND

[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

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