Question about tgsl

[kt315]

there is NOT a manual how-to-balance-coil, NOT EXISTS, just manuals how-to-make. you have to do balance yourself connecting your mind.
the forum has not possibility to keep a staff of professional consultants helping to everybody in coil bulding. no finance, we are just money-free
peacemakers.

[waltr]

How you read this:

https://www.geotech1.com/cgi-bin/pages/common/index.pl?page=metdet&file=/projects/coplanar/index.dat

[waleed]

I have found in my store a new spool of 0.85mm sized wire, it is ok to use it for building a coil?
If so,how many turns I need for tx and rx and bx?, I'll build the 10" concentric coil, I'm using the coil calculator and i thing i have no problem with Rx coil, but the problem is how many turns I need for Tx and Bx (feedback coil)?, I know that bucking coil turns depending on the number of turns for both tx and rx not only the area diameter, so in my case number of turns would change because of the size of the wire (0.85mm). So how many turns I need for Tx and Bx for that sized wire and 10" coil?

[waltr]

I also did not ground the RX coil. Works great without falsing on wet grass.
In evaluating the design I see no reason to ground the Differential RX in.

I need to play with that Nautilus circuit. I have the question of why connect the RX coil to ground and will this circuit still work without that ground connection. Have a lot of other circuits to work on so won't be getting to this one soon.

[dbanner]

That's a good question. Yes, the side connected to the non-inverting input is connected to ground on the board(battery negative). You can have a look at the Golden sabre schematic or any old tesoro schematic, they all show this end of the Rx coil is grounded.
There is plenty of discussion on another thread about falsing on wet grass with grounded Rx. I think it was said that the Rx should be left floating. You can try it both ways. In the original Tesoro units, the Rx coil is grounded at the connector internal to the main box.
My home built TGSL is with DD coil and I left the Rx ungrounded, it works excellent, no falsing on wet grass, so I left it ungrounded.
The original tesoro concentric Rx coils are tiny compared to 0.5/Tx diameter of the self made. So maybe that has something to do with it. Not sure.

[waleed]

This method seems to be good to use. I'll try it. I would ask should I ground the end wire of Rx (the one going to the non inverting) to the board gnd?

[dbanner]

With this method, all you have to do is set the correct Rx and Tx resonant frequencies, the trimmers do the rest so long as your feedback coil is within the trimmer range for nulling. (sufficiently close to null, the trimmer will fine tune the final nulling) You can make up this circuit on a small pcb which fits inside the coil housing. Many proprietry coils have similar circuits inside the housing.
Fiddling around with small loop of wire I expect is no longer required.

[dbanner]

An alternative which I never really explored but which I know works well is to introduce a feedback network of trimmers for voltage(nulling) and phase. Have a look at the nautilus feedback network. So instead of fiddling around with feedback (bucking) turns, you simply adjust trimmer pots.
One 100K trimmer nulls the Rx coil, the other 100K trimmer adjusts the phasing, so by playing with the two, you can set the concentric coil to your desired parameters. You might want to try it, if only for experiment, you can only learn more knowledge. You can use the same values as in the schematic, as the nautilus coil is almost the same as the tesoro.

[waleed]

Thanks dbanner for the useful informations...but it's really not easy to get everything right,idk which to change it's the cops or adding some extra turns to the coils,adding or subtracting a turns to the bucking coil will change the frequency of tx,idk actually.
Maybe I'll build the DD coil seems easier to do and nulling even though I like the concentric more :/, can someone with experience make it for me with enclosure? I'll pay for him.

[dbanner]

You may also consider adding some turns to your Tx coil to bump up the inductance to closer to the prescribed inductance.
A factory made tesoro concentric is always the best, but a home made always requires tinkering because of so many variables involved with the feed back coil and balancing, it is not so easy. Change the feedback turns, you change the Tx frequency, so it's a give and take scenario.

[dbanner]

Luckily for you, because your Tx inductance is a bit low, the frequency is above 15kHz, so bringing it down only involves adding capacitance in parallel with the Tx coil.
For nulling, you may have to add or subtract from the feedback turns, but it would seem that you are pretty close since your coil is working somewhat from the get-go. If you want to leave the Rx where it is and just bring down the Tx by 1.6kHz, that should be ok too.
Read through dbowers thread on tgsl concentric coil.

[dbanner]

The "off" resonances of your Tx and Rx coils must be correct, otherwise your phasing will be off and GB and disc will not be within the adjustment range of your pots.
This is why the spread is important, to keep the phasing at your null such that the Tx lags the Rx by about 20 degrees (opposite is true for DD)
The degree to which the Rx resonance differs from the Tx frequency determines the phasing, so keep this in mind.
In order to balance the concentric coil, first lock down the Rx at 16.1Khz
Then adjust the feedback for the deepest null. Don't bother too much about the Tx frequency at this stage, just null the Rx.
Finally, you tweak the tank capacitance of the Tx oscillator to get 14.5kHz.
At this point it remains to do the final nulling by moving around the extra loop from the bucking coil for the 20 degrees. It is more important at this stage to get the 20 degrees phasing rather than the deepest null.
Hope this helps.

[waleed]

in stage of testing 'on table' you do not need to shield nothing. your coil and pcb must not move.
just you begin to move a coil you must shield coil before. electrostatic field charge accumulates just in moving process in air.
in some time moment this charge has to be discharged - plus potencial on minus one (kilo-Volts, 10.000 Volts). then that gives impulse of influence and you get beep sound
in speaker.

Dam I just noticed your data joining and number of posts, it's just indicate the experience you have,nice.
Well I'll secure the coil and shield it and connect a shielding cable then I'll ground the pot. Will black when finish.

[kt315]

in stage of testing 'on table' you do not need to shield nothing. your coil and pcb must not move.
just you begin to move a coil you must shield coil before. electrostatic field charge accumulates just in moving process in air.
in some time moment this charge has to be discharged - plus potencial on minus one (kilo-Volts, 10.000 Volts). then that gives impulse of influence and you get beep sound
in speaker.

[waleed]

More progress.
Yes, best to build without nods first and get it working.

Coil resonance difference is to be evaluated by comparing the TX oscillator to the output of the RX per-amp and with test targets (coins). What coin??? A 1 Euro can be detected at 25cm on the BEST TGSL/coils, getting 20cm is good.

If the coils are not epoxied completely ridget with absolutly NO MOVEMNET vbetween them then a slight touch will move them and you get a beep.

Also, without everything properly grounded (GB pot case) and shielded

Hey waltr thank for the reply..yes I didn't properly secure the coils even didn't put a glue on the tx coil only tape,and didn't shield the coils nor the cable is shielded or grounded same as ground pot, so that would cause the beeping problem?,and how would I ground the ground pot like connect a wire from the pot on the metal side to the negative battery voltage on the board?

And I believe the depth would be improved if I get the correct resonance for the coils and then get the right null right?