TESORO GOLDEN SABRE

[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.

[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?

[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

[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.

[tiktak]

Hi,

Ok.

[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,

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

[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

[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

[zzy]

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.

[Max]

Hi,
Max.
Thanks.
You can use [email protected] !
I will be very glad to see those.
And will post some back to you.

Hi,
sent some pictures of the beast! Enjoy!

Kind regards,
Max

[nelson]

Hi Max and yhanks fot your help, cause i forgot how to do nulling with a scope.
This weekend i ll try it.
My actual coil is working good, but not has good has you, Ivconic and others did.
Thanks and best regards
Nelson

Hi,
put a suitable capacitor parallel on RX coil (like 15nF for TGS RX coil) and put a dumping resistor in parallel too (1K is ok)... then try null the best as you can lower down few mV peak peak on scope. That is about nulling.

Problem related to phase could require you choose different locations or shaping DD coils different to achieve that, but, generally the above procedure will work good.

If you cannot go down to few mVolts then you need at least 15mVpp for it to start working cool.

Kind regards,
Max

[Qiaozhi]

Hi Qiaozhi,
yes I think this is the right answer for his questions.

Let me ask you a thing that I don't have clear ...I think I read in the patents but now these informations are vanishing from my memory...

When we made disc on VLFs we compare phase on RX channels.

I mean we take quadrature samples on received signal after preamp, 90° apart one each other and so we have then e.g. 2 channels like in TGS each with its own amplitude. Then after the amplitude on these two channels are compared (Jack Gifford's patents talk about scale factor applied and then comparision made... but it's the same stuff I think) by e.g. analog stuff like op. amps and then result is applied to comparators inputs.

This actually is like extracting from RX signal the influence due to ground and ferromagnetic , and the influence of non-ferrous and compare by amplitude thus extracting a phase information related to target.

Now the question is: which relationship exist between TX signal and RX as whole, I mean... sure exist a phase relationship that rely on target composition and influence on coil... but the quadrature demodulator action is just for giving the two ferrous/non-ferrous distinct amplitudes ?

I other terms... if I wanna disc stuff cannot I just look at absolute phase between tx and rx signal (like you showed in picture, just coil phase in air there) or I need absolutely the 2 channels ???

The question is maybe a bit stupid... cause I understand that we need the two channels cause we wanna cancel out ground signal... but , in the case I wanna disc stuff just on air, isn't enough having just a look at phase between tx and rx signal ?

I made all these thoughts cause of the Ivconic's circuit about phase shift measure... that will be cool (if works good) to tune coils phase and also to disc stuff at least "on air"... to see if detector is working good or not.

Kind regards,
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.

[tiktak]

Hi,

Hi,
Max.
Thanks.
You can use [email protected] !
I will be very glad to see those.
And will post some back to you.

[Max]

Hi,
Max.
Same with me.
I dont SELL!!
I dont leave holls!!!I have seen hugh and every time I am just asking my self why they do this!!!To find some rusty nails!
But every one have a view point of his own!
Thanks for shared experiance.
Was the gold clean when you digg it?Were it deep?What was the signal?
I have found many copper bronze.Never gold or silver.
Maybe I dont tune my geb right?!??!
And like you say its wais of time,and some times when its good I find some pieces?
We will check this.From now on I will aleys carry a piece of ferite rod with me on field!
Can you post pictures of your TGS unit?

Hi tiktak,
I found a nice gold item 2 months ago with TGS in just 45minutes searching... but was luck I think cause are very rare, found also many bronze nails and other similar stuff in same place many times with TGS, and it's very sensitive to copper in soil.

Depth on this small gold target was around 13 maybe 14-15cm cannot evaluate right, not much in any case. But I found also at 22-23cm with TGS. Small stuff but consistent. When you dig that it shines in the sun... the kind of shine you don't belive the first time!

Used also in dry beach sand and found very (but very) small gold ring (I use in my air tests now) also there between a huge amount of the usual trash you find in beaches and many rusted coins! But if wet sand it's useless: no way, like other vlfs. I found the ring just near a beach-volley square... maybe some girl lost it there.

Tiktak, I think it's not a good idea posting picture in public area: I will post pictures of it to you by email, but not on forum, for the reasons of above is better avoid that, please give me your email address.

Same apply to other folks, I will send picture to anyone (trusted by me) will request but just by email, in a controlled way, and with non-disclosure agreement by them for this stuff on public area. I like privacy... you know!

I have ready pictures of it but must find (on some CD), otherwise I will made soon new and send.

Kind regards,
Max