TESORO GOLDEN SABRE

[Max]

Hi Max,

OK - I think I understand what you're asking.

Firstly, there needs to be a phase-shift (air measurement, no metal present) between the TX and RX as shown. If this is incorrect then the detector cannot find the correct ground balance point. The GEB channel should be sampling at the zero-crossing point of the RX signal where the signal is crossing from negative to positive. When metal comes close to the coil, the RX signal phase-shifts to the left, causing an increase in the amplitude for the GEB channel. If you only had the GEB channel, you would not have any discrimination. The DISC channel samples at the positive peak of the RX waveform. Non-ferrous targets cause an increase in the amplitude, and ferrous targets cause a decrease. In effect, the DISC channel inhibits the output of the GEB channel, when a ferrous target is close to the coil. By shifting the sample point in the DISC channel (with the discrimination control) you can also control the rejection of certain less conductive non-ferrous items, such as pulltabs and bottlecaps, for example.

Hi,
ok, so the GEB signal, no matter if target is ferrous or not-ferrous, will slide to left when nearing target to coil.

On the other side... when a ferrous item is neared the amplitude of DISC signal fall; when non-ferrous instead it will rise.

So you say, like in Gifford's patent I think, that you'll scale disc channel level in a way it will compensate the geb channel level increase by same but reversed in sign (decrease) action due to ferrous target, thus resulting in an opposition or subtraction when ferrous stuff, and instead sum when there's a non-ferrous target.

When non-ferrous the geb channel out increase will actually sum with the disc channel output increase to give a "boost" on actual detection behaviour, so this will increase also SNR in some way cause will be superimposition of two effects, geb increase and disc increase.

Am I right on this ?

So the principle is... I will disc sliding the disc sample in a way I will consider in-phase components give me maximum amplitude, so other angles that will make the maximum of wave slide left or right of the sample interval will give actually a discrimination like could happen with foil when you set disc in a way the shift due to foil will be not enough to center maximum peak of wave exactly in the middle of sample interval.

But that doesn't actually mean there's also a phase shift due to target ?

Another thing:
I mean... I always thought at quadrature demodulator like something truly acting 90° apart about pulses sequence but seems here you set geb with one control and disc with another... thus giving not exactly 90° shift from one another in the general case but just "about" 90°, sometimes e.g. 85° , sometimes maybe 95° or 100°.

So in TGS, formerly speaking there isn't any quadrature demodulator, apart the case when you fix samples exactly at 90° shift using geb and disc knobs: the only case where signals are really in "quadrature" to exactly 90°.

If all this is right why the hell we still call it quadrature-demodulator ???

Now another question: suppose you can measure absolute phase of RX signal at output of rx amplifier respect to tx signal (reference) with very hi accurancy.

Now suppose you will do that on air: you will read rx-tx phase shift due to coil only when in air and no target near.

Then suppose you lower the coil on soil and then measure again the phase shift: you'll sure will read a different value than before, due to ground effect.

Suppose then you will consider that ground reading your zero phase, like moving the needle of an old IB/VLF to the central zero: will you read any target signal phase variation as positive or negative then to the zero point ?

What I'm asking here... is... Is right if I assume 2 phase components effects from a target buried in soil (one due to soil only, and the other due to target only) that actually give you the composite effect on RX signal ?

I think it's so... and when we do GEB tuning on soil... we actually rotate the coordinate system to make the component due to soil only give no effects on the disc channel signal , cause its projection on it is zero, since the 2 channels have input at a real quadrature demodulator to are 90° truly shifted.

If so, zzy is right and we lose some GEB nulling when in TGS cause it has not always a quadrature-demodulator action.

Sorry for the long post... but I have this dubt also before... but don't wanna make people spend much time on details of TGS design or mistakes before they show up like in this case.

Kind regards,
Max

[Max]

Hi,
I forget to say a thing in last post:

Sorry I must clear this: I didn't consider relative amplitude of grond signal and target signal in the example of above... but just phase. Sure the system of above will never work in real world (cause ground signal is maybe thousand times greater than signal due to eddy currents in target)... unless we consider TOTAL cancelling of ground signal influence due to rotation...things that happens just in a particular case in TGS (at right positions of both geb and disc control knobs)... but the example is just to understand better how things go there.

Kind regards,
Max

[tiktak]

Hi,

Hi,
Max.
Thanks for the pictures I saw those.
Did you check my e-mail?

[Max]

Hi,
Max.
Thanks for the pictures I saw those.
Did you check my e-mail?

Hi,
no I will check later... and let you know.

Kind regards,
Max

[tiktak]

Hi,

Ok.

[Qiaozhi]

Hi Qiaozhi,
"The GEB channel should be sampling at the zero-crossing point of the RX signal where the signal is crossing from negative to positive."
It's seems reasonable,but in practice,it's not that.If you sampling at the zero-crossing point,you can't balance the ground.I find that the ground can also causes phase-shifts.

Actually, in practice, that is exactly how it works. Of course you are correct that lowering the coil to the ground may cause some phase-shift, depending on how much mineralization there is in the soil. This is why detectors like the TGS do not work very well in Australia. This is also the reason why an external GEB control can be useful. When you go through the ground balancing procedure (i.e. bobbing the coil up and down, while adjusting the GEB control) you are again moving the sample point to the zero-crossing position to compensate for the ground. For detectors that have a factory-set ground balance setting, I believe that the sample point is offset by about -5 degrees. This allows the detector to be used over a wide range of different soil types without too many problems.

Another thing:
I mean... I always thought at quadrature demodulator like something truly acting 90° apart about pulses sequence but seems here you set geb with one control and disc with another... thus giving not exactly 90° shift from one another in the general case but just "about" 90°, sometimes e.g. 85° , sometimes maybe 95° or 100°.

So in TGS, formerly speaking there isn't any quadrature demodulator, apart the case when you fix samples exactly at 90° shift using geb and disc knobs: the only case where signals are really in "quadrature" to exactly 90°.

If all this is right why the hell we still call it quadrature-demodulator ???

Good question...
The answer is that it's really called a synchronous demodulator, but some people have also referred to this as a quadrature demodulator. The main reason is because the GEB channel samples at the zero-crossing position, and the DISC channel samples 90 degrees (pi/2) later at the peak of the RX waveform. In this way you have a ferrous/non-ferrous detector. However, if you adjust the DISC control, then you are correct - the two samples are no longer 90 degrees apart.

[Max]

Actually, in practice, that is exactly how it works. Of course you are correct that lowering the coil to the ground may cause some phase-shift, depending on how much mineralization there is in the soil. This is why detectors like the TGS do not work very well in Australia. This is also the reason why an external GEB control can be useful. When you go through the ground balancing procedure (i.e. bobbing the coil up and down, while adjusting the GEB control) you are again moving the sample point to the zero-crossing position to compensate for the ground. For detectors that have a factory-set ground balance setting, I believe that the sample point is offset by about -5 degrees. This allows the detector to be used over a wide range of different soil types without too many problems.


Good question...
The answer is that it's really called a synchronous demodulator, but some people have also referred to this as a quadrature demodulator. The main reason is because the GEB channel samples at the zero-crossing position, and the DISC channel samples 90 degrees (pi/2) later at the peak of the RX waveform. In this way you have a ferrous/non-ferrous detector. However, if you adjust the DISC control, then you are correct - the two samples are no longer 90 degrees apart.

Hi Qiaozhi,
thanks for answers. You forget last question:

if we have a very accurate phase meter, then null to zero reading when coil is put on soil like at geb tuning, can't we actually disc buried targets then by just considering absolute phase shifts ?

I mean... we should have positive shifts for non-ferrous and negative for ferrous. I think this is the general Ivconic's idea of using a phase meter to check for metal kind as used also in older VLFs.

What do you think about ?

Kind regards,
Max

[tiktak]

Hi,

Hi,
Ivconic.
Did you ever tryed to test TGSL with that original coil that you have from your broken RH?
Buy the way what is the probleme with this preshes piece?

[Qiaozhi]

Hi Qiaozhi,
thanks for answers. You forget last question:

if we have a very accurate phase meter, then null to zero reading when coil is put on soil like at geb tuning, can't we actually disc buried targets then by just considering absolute phase shifts ?

I mean... we should have positive shifts for non-ferrous and negative for ferrous. I think this is the general Ivconic's idea of using a phase meter to check for metal kind as used also in older VLFs.

What do you think about ?

Kind regards,
Max

Hi Max,

How the RX signal phase-shifts, and what happens to the amplitude for various targets, very much depends on the coil configuration. For the Tesoro coils they all produce a phase-shift to the left for all targets, and the amplitude increases for non-ferrous, and decreases for ferrous. This can be easily confirmed by monitoring the RX signal at the output of the preamp with a scope, while triggering from the TX signal.

Yes - you could directly measure the phase-shift in the RX signal relative the TX and display this on a phase meter, but the phase measurement is also dependent on the distance of the target from the search coil. This is why target ID is so unreliable, and you can often end up digging a really deep hole and finding a nail.

The 2-channel approach is a simple elegant way of solving the discrimination problem, even though it's not perfect.

[Max]

Hi Max,

How the RX signal phase-shifts, and what happens to the amplitude for various targets, very much depends on the coil configuration. For the Tesoro coils they all produce a phase-shift to the left for all targets, and the amplitude increases for non-ferrous, and decreases for ferrous. This can be easily confirmed by monitoring the RX signal at the output of the preamp with a scope, while triggering from the TX signal.

Yes - you could directly measure the phase-shift in the RX signal relative the TX and display this on a phase meter, but the phase measurement is also dependent on the distance of the target from the search coil. This is why target ID is so unreliable, and you can often end up digging a really deep hole and finding a nail.

The 2-channel approach is a simple elegant way of solving the discrimination problem, even though it's not perfect.

Hi,
I noticed some stranges on my original Tesoro-coil (8x9'' spider) but cannot understand when you say that all targets give left shifts, cause also Gifford's patents report devices rely strictly on phase shift detected at RX coil signal.

In picture I captured a part of patent reporting phase shifts for various metals and mineral soil.

How could be possible that targets produce just left shifting of RX waveform and detectors works just considering amplitude of RX signal there ??? Seems impossible to me the things go that way.

Let me explain... I know the amplitude shift happens and are present on RX signal at preamp out BUT on disc channel ,after demodulator, this is due to positive or negative phase shift the RX signal is subject to cause of a target.

The demodulator idea rely on this stuff: if you can disc just considering the rise or fall of amplitude signal at preamp out, why the need of a sync demodulator there ?

Consider the dashed line in the picture: there is the sample for disc channel... as you can see sampling there "good" targets (non-ferrous) will give a rise in amplitude and "bad" (ferrous) like iron nail will give zero and mineral soil negative amplitude shift. But this just cause of RX signal phase shift.

Am I wrong on this ? Maybe I miss something or made some mistake...

Kind regards,
Max

[Max]

Hi,
I've tested again my Tesoro coil... and got results like you wrote about (now I remember I saw this stuff during bandidoII cloning but then forgot about).

The RX signal shift always to the left, no matter of target composition.

The question is now... what's the purpose of the diagram of above when in their coils the phase shift is always one way no matter of target?

I understand even less now!

Maybe the reference point is somewhere else than at zero crossing of TX ???

Kind regards,
Max

[Qiaozhi]

Hi,
I've tested again my Tesoro coil... and got results like you wrote about (now I remember I saw this stuff during bandidoII cloning but then forgot about).

The RX signal shift always to the left, no matter of target composition.

The question is now... what's the purpose of the diagram of above when in their coils the phase shift is always one way no matter of target?

I understand even less now!

Maybe the reference point is somewhere else than at zero crossing of TX ???

Kind regards,
Max

Hi Max,

I am pleased that you have independently confirmed that all the phase-shifts are to the left. Otherwise this was going to get complicated to explain.

As far as the GEB channel is concerned, only metal targets cause a phase-shift. As these shifts are always to the left, a positive signal is generated that causes an audible beep in the headphones. That's why sampling at the zero-crossing is necessary. The ground (if not mineralized) only causes a change in amplitude, but no phase-shift. Hence there is no audible beep when the coil is lowered to the ground.

For the DISC channel, the discrimination relies soley on amplitude changes - increase for non-ferrous and decrease for ferrous.

The confusing thing about the diagram in the Gifford patent is that the phase readings are taken relative to the TX signal, and this is why you end up with positive and negative phase values.

[zzy]

Hi,
I've tested again my Tesoro coil... and got results like you wrote about (now I remember I saw this stuff during bandidoII cloning but then forgot about).

The RX signal shift always to the left, no matter of target composition.

The question is now... what's the purpose of the diagram of above when in their coils the phase shift is always one way no matter of target?

I understand even less now!

Maybe the reference point is somewhere else than at zero crossing of TX ???

Kind regards,
Max

HI Max

"The RX signal shift always to the left, no matter of target composition."
???
No, my test is all metal the RX signal shift always to the right,but the ferrite is shift to the left.

[Max]

HI Max

"The RX signal shift always to the left, no matter of target composition."
???
No, my test is all metal the RX signal shift always to the right,but the ferrite is shift to the left.

Hi,
I'm totally sure of that. I checked yesterday with my original tesoro coil (9x8'' )and shift happens to the left with metals.

I tested many stuff, iron, copper, silver, gold, brass, bronze... etc always RX signal shift to the left side.

I think you have to reverse RX coil leads to gain good disc and have same kind of shift there.

Kind regards,
Max

[ivconic]

"..The ground (if not mineralized) only causes a change in amplitude, but no phase-shift. Hence there is no audible beep when the coil is lowered to the ground...."

This is true and very useable to know when nulling coil.
Using ferrite rod man can simulate partially ground conditions.My reference when nulling coils is situation when scoped RX only react by huge amplitude rise without producing any sound, on closing rod to coil surface. Monitoring residual voltage and RX scope i adjust coil to achieve that situation without worries on other things. Once i achieve minimal residual voltage and adjust GEB not to produce audio on rod i know coil is properly nulled.
In theory this method could be argued, in practice such coils are shoving really best performances in 100% cases. Rock stabile and excellent depths.
I didnt scope phase angle preciselly due bad and obsolete scope i have.
Yet i noticed one more interesting thing;
let's presume coils are nulled and RX having residual voltage 5mV, closing iron claws transversely to coil surface voltage rises from 5 to ...let's say 15mV.
But what really suprised me is when i turn same iron claws perpendiculary respecting coil surace, voltage drops fast to 1mV and even zero!!!?
What is going on here? Sheesh! I dont understand this!?
Iron claws in other orientation seems to "suck" voltage?
Same case was with some Cu alloys!? Same Cu alloys are bairly detectable with ordinary PI detector (as i noticed previously)????
Another case is "ring" phenomena; circle shaped piece of metal would be good detected, yet if we drill a hole in it - it would be much louder detected!
Take a coin drill 5mm hole in its center. Than try to detect it. You will be amazed of much stronger signal it would produce than!
Some (very few) alloys do "suck" induced voltage, yet some do amplify it more.
Phase shift meter i tried to achieve turns to be pretty unprecize and unaccurate. I am searching better method (simplier than scope) to monitor this on various items and metals.
Regards!