Silver sabre coil problem

[Massimo]

Hi all
I have built silver sabre plus and it go but there are same problem .
I built a DD 20cm in diameter coil and and i mach it at 10KHz, i have on Tx 9 9.5 volt and on rx i can go around 20-30 mv, the Tx and Rx are equal in form and number of turns so i presume that there isnt difference on which are tx and rx.
Each coil have schield and one estreme of the winding is put on shield and other is free so i have a shielded cable with 3 wire tx,rx and ground.
When i put wire on pcb in a order , in disc, i can heard a copper coin at 22-25cm in air and i have a little discrimination power but if i reverse wire Rx- Tx i cant have any signal from copper coin never from a 1Kg hammer at 1-2 cm and never fron a pcb 10x15 but a can heard a little allumium coin at 15 cm.
In all metal there are no difference and i can heard a copper coin at raffli 22 cm ,is not important in which order tx and rx are put.
What about?
It seem that coil have a phase degree and one time i add phase degree of coil whit degree from circuit and in the other case i subtract it.
May be this an explanation ? and how i can solve problem or how can built a different coil like concentric or coaxxial?
This is may first motion and i have learn a lot on motion machine and filter, i like this unit and i will happy it go at better.
Any help is appreciate
Thanks in advant
Massimo

[Carl]

Re: Silver sabre coil problem

There may be an issue with coil alignment, versus the direction of the winding. You say you have 20-30mv on the RX coil -- is that static, with no target? If so, then that residual signal (due to minor misalignment) has a certain phase to it.

Now introduce a target, and you will either add to that signal, or subtract from it. Whether it adds or subtracts will depend on the relative winding directions of the TX and RX coils, and the type of target metal, which determines phase. It might be possible that in the second hookup you are getting cancelation in certain cases.

- Carl

[Reg]

Re: Silver sabre coil problem

Hi Massimo,

I would think the receive coil has to be phased properly for the detector to work at all in either the discriminate or the discrimination mode.

Even though yours does work, I would still be inclined to believe that your phasing is off quite a bit. Any phasing problem would quickly show up in the all metal mode when you tried to ground balance the detector.

Most IB detectors I have used have many more turns on the receive coil than they do on the transmit coil. So, I would be inclined to think that maybe you do not have enough turns on the receive coil.

I would probably try at least a 5 to 1 ratio. In other words, if the transmit coil had 30 turns, then the receive coil would have 150 turns.

Getting back to your original question if the phasing is important, my guess is yes, the phasing is very important.

Reg

[Massimo]

Re: Silver sabre coil problem

Thanks for answer Carl
I do a mistake, i have 30mV not on rx coil but after front end, the gain of front end is about 30 so i think i have about 1-2 mV on rx coil.
Do you think i must go to 0 mV on rx? No signal no phase with it, I suppose.
If i built a coil with a circolar tx coil 20cm diameter, resonantig at 10KHz, and a rx circolar coil 10 cm in diameter put in the middle of Tx; but with Rx divided in 2 equal number of turn, first half turns clockwise and second half turns anti-clockwise .
If the 3 coil are aligned on the same axis i think they pikup 0 signal .
Do yoy think this is a good idea?
Massimo

[Massimo]

Re: Silver sabre coil problem

Hi Reg and Carl
Now i have understand that is important the level of signal on rx but even important is the phase of rx signal!
But how i can control or match the phase in rx coil?
You said to use more ( 1@5 ratio) turns on rx coil but is a good idea even on a DD coil? Because the DD i have seen before have same tx and rx turns.
Thanks Massimo

[Reg]

Re: Silver sabre coil problem

Hi Massimo,

I know that DD coils on PI's generally use the same windings ratio to keep the timing constant. However, my experience with DD coils is very limited and the only one I experimented with a lot had a turns ratio like I mentioned. However, that was not a Tesoro. One other DD coil I have which again is not a Tesoro has a turns ratio of 3 to 1.

So, I may have given you incorrect information when I suggested you try a different turns ratio for the SS.

I found a good Tesoro DD coil I tried to measure a Tesoro DD coil and got mixed results with the wiring attached.

I also found an old Tesoro DD coil that has been taken apart but the wiring is no longer connected so I cannot say for sure how it was wired to the plug. In measuring this DD coil, I found that one coil winding has 6.13 mh and 85 ohms.

I have no way of measuring the wire size but the windings all look like they are using the same size wire.

The other main winding appears to have two separate windings wound together, with both measuring about 1.49 mh and 19 ohms. If this is the receive winding and the winding measurements I have are for a center tapped coil, then it appears the tx to rx ratio is 1:2.

After looking at the circuit, it is possible the receive coil is center tapped. This would make sense. That would be the proper way of using the differential amplifier circuit as drawn.

Since your detector is working in the all metal mode, and if you have a dual trace scope, you can observe the different signals at various IC outputs to see if they are correct.

However, I wouldn't think you could detect an object correctly if you reversed the windings. So, I suspect your phasing is way off.

Does the ground balance work? If it does, I would think your phase is close to being correct. Right now, I suspect it does not work correctly.

What kind of signal do you get from a piece of ferrite like an old radio antenna or a ferrite core from a switching power supply? If the phasing is correct, you should be able to adjust the ground balance pot and make the ferrite go from a - signal to a + signal and be able to find a location on the ground balance control where the ferrite gives a minimum response.

One other point, I would keep the ferrite a few inches from the coil when checking. Just have it close enough to see what kind of signal it gives. If you get the ferrite core too close to the coil, you can get mixed results.

I would try to be able to get the ferrite test to work first. If you can't obtain the ferrite adjustments, I would try changing the cap across the receive winding, trying either a larger or smaller one until I got the desired ferrite indications. Once you are able to this, then the ground balance should work.

If the ground balance works, then I would think the disc mode should be be close to working.

Reg

[Marcello]

Re: Silver sabre coil problem

Hi Reg and Carl,
I ask to you that you are the mind of this forum and that you help who is really impassioned of electronics.
Also I have built the Tesoro silver sabre plus from the electric scheme published on this forum in precedence.
Also I have the same problems of Massimo.
The scheme of the tesoro silver sabre plus has me really impassioned because didactically it is really valid and functional, however the construction of the heads of search they imply of the studies and of the calculations that are not to my course.
Shortly I reassume you my experiments hoping that you succeed in helping to make me correctly work it.
I have built first a ddcoil from 20cm with 118 turns (to make to oscillate it to 10KHz) both for tx that rx, with wire from 0,35 mm. The resistance of the coils tx and rx is 8 ohms.
The performances have been scarce and besides the oscillator of colpitts produced me a wave distorted.
Then I have wound the two coils with 118 turns with wire from 0,25 mm.
The resistance of the coils rx and tx it is 30 ohms.
with this section of wire the oscillator of colpitts regularly works however the depth of search doesn't overcome the 10-15 cm in air.
In base to your affirmations should leave the coil tx with 118 turns (to make to oscillate it to 10Khz) and the coil rx with a different number of turns!

Then if someone knows how to tell me the value ohm of the coils rx and tx of a ddcoil Treasure I would succeed in drawing the number of turns of both the coils (supposing to use the same section of wire).

You excuse not the prolixity and the very correct English.

Thanks to everybody!

[Massimo]

Re: Silver sabre coil problem

Hi Reg
I try to change the form of DD from circular to elliptcal 16x24 cm.
Now i have this data:
Tx F = 10kHz, amplitude 8 V P.P.
Rx = 10-12 mV mesured on coil and not after front-end, capacitor in parallel with rxcoil 47nF.
With a dual trace scope i chek phase degree in conparison of Tx signal.
I have this data:
degree on Rx coil =36°
total degree after G.B. comparator from 0 to 36°(from Min To Max on trimmer)
total degree after disc comparator 0 to 100-110°.(from Min To Max on trimmer)
If i change the capacitor in parallel with rx coil from 47nF to 22nF i have 5 mv level on Rx coil and a degree of 90°.
In all position (all metal) of GB trimmer i cant nulling signal from a ferrite cilinder 1cm in diameter and 3 cm long but in disc. i can find a position on disc trimmer after which i can nullig respons from ferrite.
I suppose that your suggestion to try with a piece of ferrite is to simular a hevy mineralition condition, is this correct?
May be the piece of ferrite too large for nulling in all metal? Or i would nulling it in every case for a correct operation?
When you said a center tape rx coil you said a rx coil with the center turns put at ground?
Thanks in advant Max

[Reg]

Re: Silver sabre coil problem

Hi Massimo,

You want to use a piece of ferrite to assure the phasing is correct between the coil and the associated all metal mode circuitry.

I suspect the size of the ferrite isn't the problem As long as you keep it some distance from the coil when testing.

You just need the ferrite close enough to the coil to determine what type of signal you are receiving. By this I mean, if you can adjust the GB pot and cause the ferrite to null, or not give much of a response.

If the phasing is correct, then passing a piece of ferrite across the coil should give a negative response with the GB pot at or near one end, and a positive response when the pot is adjusted to the opposite end or close to it.

Somewhere in the middle, the ferrite should give almost not signal. Remember to keep the ferrite a few inches from the coil when making this test.

Yes, using the ferrite is done to assure the circuitry is adjusted properly.

Since your detector appears to null the ferrite in the disc mode, then your phasing is incorrect. You may have to swap the receive leads as well as make a capacitor change across the receive coil to obtain the proper results.

As for the information I mentioned about the Tesoro DD coil. I suspect the center tap of the receive coil is tied to ground.

Many VLF's having an internal ground balance pot are set up using a piece of ferrite as a reference.

Again, to be sure your phasing is correct, just try to select the proper cap to obtain the ferrite results I mentioned. Once you have done this, then check your disc mode.

Reg

[Massimo]

Re: Silver sabre coil problem

Hi Reg
I do a lots of test with DD but but i cant have good results.
So i try built a new coil. ( samething like a concentric)
Tx circolar coil 110 turns 20cm diameter and Rx bifilar 85 turns 8 cm diameter put in the middle of tx.
I center tapped rx coil and put the center at ground.I put two rx coils in phase so i have two equals signal with same phase at the input of differential stage.
At the output af differential i have a sinusoidal signal at about 50-60 mv.
In this way i thought nulling signal from rx coils, but i null even signal coming from metal!
Infact if i put a big metal piece near coils and look rx signal with scope i see there arent difference in amplitude, i have a little signal only at 1-2 cm.
So i think this is not the good way .
But how can i built a coil DD, coaxial or concentric for tesoro detector? Or where can i have informations on building coils?
Thanks in advant
Massimo

[Reg]

Re: Silver sabre coil problem

Hi Massimo,

Just changing the way the rx coil connects to the opamp will not correct your problem. You have an additional phase error that has to be corrected.

In the all metal mode, you shouldn't be nulling on an iron object. It almost sounds like you have some other thing wrong.

Any iron nulling should be done in the disc channel and not the all metal channel.

I am curious if you tried the ferrite test. If you did, you might want to check to see if it nulls in the disc channel. If it does then you some serious phase shift problem, that can't be corrected by simply winding a different coil.

If the ferrite does null in the disc channel, then you might want to try to swap the signals going to the FET sample transistors and see what happens.

Again, you might also try different capacitors across the receive coil to change the phase shift to see if you can get the ferrite to null instead of the iron in the all metal mode.

Reg

[Massimo]

Re: Silver sabre coil problem

Hi Reg
I think that on schemas of silver sabre post on forum there is an error.
One wire of rx coil is put at ground and so i presume that differential stage dont work well, in this mode i think it work as a normal amplificator and not as differential.
I cut off the copper on pcb and isolated rx pad from ground and now in all metal i can nul ferrite piece. In disc i have again same little problem, i havent a clear difference between iron and not iron, but i think now is only a problem to find right value for disc capacitor.
All right is not a monster of power( a copper coin at 20-22 cm in air) but now that it seem going there are space for inprovement and experimentation.
Thanks for your help Reg
Massimo