TESORO GOLDEN SABRE

[Aziz]

Hi,

I observed on DD coils phase anomalies on metal pins (like drills). The phase shift is dependend on target shape, orientation and on placed coil position.
Please, check this out.
Aziz

[Max]

I think Max said that he could confirm there was a phase-shift to the left with a Tesoro factory-made concentric coil, but do not remember what he found with the DD.

Actually, the difference in phase-shift direction will produce different results. For the concentric coil, a left-phase shift means that the target is detected as it enters the RX coil, whereas a right phase-shift will only detect the target as it leaves the RX coil, which makes it more difficult to pinpoint amongst the trash. For a DD coil, the effective detection area is a thin strip in the middle of the coil that runs from front to back. In this case there would be little difference between a phase-shift in either direction, due to the narrowness of the detecting area.

Regarding whether a concentric or DD coil is the best, is often a matter of preference. You have to overlap consecutive sweeps with a concentric, which means that the area cannot be covered so quickly. But they do have superior pinpoint capabilitie,s and are better at picking out targets in trashy or iron-infested areas. DD coils have a wider sweep area, and there is no need to overlap sweeps, and are also less affected by ground mineralization. I believe that Tesoro ship their detectors with concentric coils because these give the best overall performance for the greatest number of customers.

Hi,
yes my original 9x8'' shift to the left; I suppose all concentric by tesoro are this way, like you stated... but have just the 9x8'' original and didn't test others for phase till now.

I remember also that all my DD shift one way... but now I don't remeber now if left or right ...must check again in some spare time (if I find some I mean... very busy these days).

Kind regards,
Max

[Max]

Hi!

I have redy the next coil DD255x137.Results are very good 35-40cm with 3cm coin.Disc. also work correctly.Still i heve next problem,when the coil is puted on the desk work good.But when I bring him from desk detector start self oscilating,and only can hear beeb.It is same if i stroke to the desk.

Hi,
ok...I suppose you didn't fix it already so you need to epoxy it... of fix in another way but very tight and avoiding any movement relative tx/rx . Any vibration would change coupling between tx and rx and so you get false signals when move the coil.

We discussed fixing with epoxy somewhere before : you need liquid epoxy stuff to do perfect way. Can use also other stuff but I suggest epoxy expecially clear one used for surfboards: I found it extremely good for coils.

Kind regards,
Max

[nelson]

How i can measure RX frequency, to know if RX coil is resonating at 16.XXX Khz?
Regards
Nelson

Hi Qiaozhi,

I've read many posts on Tx frequency of ~14.6 KHz here, but where does the Rx frequency (16.12 KHz) you stated above come from?

Will try swapping coils tonight...

Thanks,

Molzar

[scevlik]

Hi!

I have redy the next coil DD255x137.Results are very good 35-40cm with 3cm coin.Disc. also work correctly.Still i heve next problem,when the coil is puted on the desk work good.But when I bring him from desk detector start self oscilating,and only can hear beeb.It is same if i stroke to the desk.

[Qiaozhi]

Hi Qiaozhi,

So with DD or OO coil configuration shift is to the right. Didn't Max get shift to left? or was he using concentric coil?

Interested in why "direction of phase shift is not a problem" on TGS. Can you please explain? Why do you think Tesoro deliver concentic coils, why is better?

Molzar

I think Max said that he could confirm there was a phase-shift to the left with a Tesoro factory-made concentric coil, but do not remember what he found with the DD.

Actually, the difference in phase-shift direction will produce different results. For the concentric coil, a left-phase shift means that the target is detected as it enters the RX coil, whereas a right phase-shift will only detect the target as it leaves the RX coil, which makes it more difficult to pinpoint amongst the trash. For a DD coil, the effective detection area is a thin strip in the middle of the coil that runs from front to back. In this case there would be little difference between a phase-shift in either direction, due to the narrowness of the detecting area.

Regarding whether a concentric or DD coil is the best, is often a matter of preference. You have to overlap consecutive sweeps with a concentric, which means that the area cannot be covered so quickly. But they do have superior pinpoint capabilitie,s and are better at picking out targets in trashy or iron-infested areas. DD coils have a wider sweep area, and there is no need to overlap sweeps, and are also less affected by ground mineralization. I believe that Tesoro ship their detectors with concentric coils because these give the best overall performance for the greatest number of customers.

[Molzar]

Cable

Nelson,

I use Belden 8723. This is foil sheilded (2) twisted pair, very nice!

Also you could used (2) RG174U (thin) coax cables. (like for scope probe)

You could even use (for bench testing) (2) regular coax (RG6, RG58 or 59).


Molzar

[Molzar]

At last I've found some time to test the overlapping coil configuration that most of you are using to build your homemade coils. The Tesoro factory-made concentric coils are all constructed to provide an initial phase-shift between the TX and RX of about 120 degrees, with the RX signal measured at the output of the RX preamp. All targets give a phase-shift to the left, with ferrous targets causing a decrease in amplitude, and non-ferrous causing an increase.

I constructed a simple test using two round coils of 180mm diameter. The TX coil consisted of 115 turns of 0.56mm enameled wire (5.6mH) and the RX had 122 turns (6.5mH). I was really trying for 5.9mH on the TX, but this discrepancy will not affect the test.

To get the correct 120 degree phase-shift between TX and RX, it is necessary to gradually move the two coils together until you reach a null point, and then go through the null until you have a few mV at the RX input. You can find the null point more easily by monitoring the preamp output with a scope. In this position, ferrous objects will cause a decrease in amplitude, and non-ferrous will cause an increase. However, all metallic objects will cause a phase-shift to the right. This is, of course, different to the concentric coils, but because of the way this type of analogue detector works, the direction of phase-shift is not a problem.

After some experimentation with this test setup, it is clear why Tesoro deliver their detectors with concentric coils. Has anyone tried constructing an omega coil for the TGS? I would think that the omega would be much easier to set up than the concentric, and may perform better than the DD.

Hi Qiaozhi,

So with DD or OO coil configuration shift is to the right. Didn't Max get shift to left? or was he using concentric coil?

Interested in why "direction of phase shift is not a problem" on TGS. Can you please explain? Why do you think Tesoro deliver concentic coils, why is better?

Molzar

[Fred]

Tiktak,
Also i think you mentionned before that you did not clean your PCB.
You MUST, also you must be sure you used a non-acidic solder flux,if you used some, or else you will have to make a new PCB...

regards,
Fred.

[Qiaozhi]

Hi,
Max.
Its look like I havent solved the probleme afther all!
Still this week beeeeeeeeeeeeeep all the time.
The 22 ohm resistor were burned and I replaced it but this didnt solved the probleme.The funniest thing is that this morning I bwol air against the PCB from the left short side and this sound stop.But afther a while it begins again.What is this?
Also I have used your pictures and make the same coil but when I attach TX to PCB the frequency is 28,2 kHz???????Why?
Please check the numbers again!I see:11,4;12,5;12,75;13,35;13,7 and 1,6cm~!~~~
Right.
Tx=100w 0,25
Now I have cheked on my old PCB also around this frequency but working desent.
Hum......................

Hi Tiktak,

First - I would check all your power supply voltages, not just at the output of the regulators, but also at the power pins of the ICs, in case there are any wiring errors.
Are all your ICs in sockets? If so, then this could easily be the cause of your problems. In particular, the comparator IC should not be socketed. In the TGS circuit, the comparators are responding to relatively slow input signals that tend to hover around 0V. This can easily cause the comparators to go into oscillation. Try monitoring the comparator outputs with a scope to see if this is happening. These oscillations can be avoided by soldering the IC directly to the PCB (not using sockets), by using good PCB layout techniques (ground plane under the IC), and/or by adding a capacitor across the input terminals. A value between 100pF and 1nF should be sufficient. It may even just be a case of adding a 100nF decoupling capacitor across the power pins. If all these methods fail to remove the oscillations, then you will need to add some components around the comparators to provide hysteresis, although presumably the original TGS does not suffer from this, and it really should not be required.

Of course, this may not be the cause of the problems, but that's where I would start my investigation, after checking the power supplies.

[tiktak]

Hi,

Hi,
Max.
Its look like I havent solved the probleme afther all!
Still this week beeeeeeeeeeeeeep all the time.
The 22 ohm resistor were burned and I replaced it but this didnt solved the probleme.The funniest thing is that this morning I bwol air against the PCB from the left short side and this sound stop.But afther a while it begins again.What is this?
Also I have used your pictures and make the same coil but when I attach TX to PCB the frequency is 28,2 kHz???????Why?
Please check the numbers again!I see:11,4;12,5;12,75;13,35;13,7 and 1,6cm~!~~~
Right.
Tx=100w 0,25
Now I have cheked on my old PCB also around this frequency but working desent.
Hum......................

[Qiaozhi]

Homemade coils

At last I've found some time to test the overlapping coil configuration that most of you are using to build your homemade coils. The Tesoro factory-made concentric coils are all constructed to provide an initial phase-shift between the TX and RX of about 120 degrees, with the RX signal measured at the output of the RX preamp. All targets give a phase-shift to the left, with ferrous targets causing a decrease in amplitude, and non-ferrous causing an increase.

I constructed a simple test using two round coils of 180mm diameter. The TX coil consisted of 115 turns of 0.56mm enameled wire (5.6mH) and the RX had 122 turns (6.5mH). I was really trying for 5.9mH on the TX, but this discrepancy will not affect the test.

To get the correct 120 degree phase-shift between TX and RX, it is necessary to gradually move the two coils together until you reach a null point, and then go through the null until you have a few mV at the RX input. You can find the null point more easily by monitoring the preamp output with a scope. In this position, ferrous objects will cause a decrease in amplitude, and non-ferrous will cause an increase. However, all metallic objects will cause a phase-shift to the right. This is, of course, different to the concentric coils, but because of the way this type of analogue detector works, the direction of phase-shift is not a problem.

After some experimentation with this test setup, it is clear why Tesoro deliver their detectors with concentric coils. Has anyone tried constructing an omega coil for the TGS? I would think that the omega would be much easier to set up than the concentric, and may perform better than the DD.

[nelson]

Ok, thanks Ivconic. I ll do the search.
regards
Nelson

Usb? Dont know. Maybe it is not so suitable to be used there? I am not sure.
Search net for Belden cables, explore its specs and try to find simillar one...already proven as very good to be used here.

[ivconic]

Usb? Dont know. Maybe it is not so suitable to be used there? I am not sure.
Search net for Belden cables, explore its specs and try to find simillar one...already proven as very good to be used here.

[nelson]

Thanks to everyone.
My new coil has the same data has yours Ivconic. Noew i gain a few more cms (24 for a 26mm copper coin)
I also place new LM308.
The coil was nulling with the scope, no problem:
Now i m focusing on cable. I m using usb cable, but i have heard that this is not good for VLF detectors. So what capacity should i use , lower or higer?
Ivconic, this weekend i ll try to open my Gold Bug2. This is also important to me cause i whant to know if is possible to mod the detector to allow full discrimination, instead of fix discrimination (all metal/iron reject).
Regards
Nelson

Indeed. "Wildly" adjusting GEB trimmer there will affect phase to much.Not comfortable and easy in real conditions on the field.Operater must pay a lot of attention on pot. position.