TESORO GOLDEN SABRE

[Qiaozhi]

Indeed, and real goal would be to achieve less phase shifts, influenced by depth rises. Same old problem; some medium sized iron at greater depths will be detected as "coloured" by many detectors not only TGSL in the soil especially.
TGSL has weak TX. Is it possiblle to overcome phase issue with stronger output? At least to expand accuracy at a bit greater depths... I think it is possiblle. Stronger output will expand accuracy and phase would be slightly shifted at greather depths than it is now. But stronger TX will cause many other problems, stabillity issue at first place...
Would be good to analyze disc circuitry at White's Eagle, XLT,MXT,M6 and DFX serie. Those are accurate up to some point and VDI shows real numbers, but after some point those do not showing any number, just undefined audio on deep detections.... So problem is not solved at those models but also those do not "claim" deep items as "coloured" or iron. Just producing audio at detection of those deep items. Smart done.

Unfortunately you are up against some basic physics here. The way the Whites (or any other digital detector) displays "accurate" VDI numbers, is by having a lookup table in ROM of various phase angles measured for specific targets at various depths. By monitoring the amplitude and cross-referencing this with the lookup table, it is possible to "guess" the identity of the target. This is only really accurate when the target is relatively close to the coil, or when performed in an air test. The ground causes lots of distortion in the RX signal, which makes the target id inaccurate.
There is no easy way around this problem with an analog detector.

[ivconic]

Hello Ivica Do you know if Roberts will be at belligrad at 7....8/11. I want to meet him
Please contact with him and tell me.
Regards

So as i heard from him, he is in Germany and will stay there till christmass.

[ivconic]

Simply monitor the output signal from the pre-amp relative to the TX signal. You will need a 2-channel scope to do this. Trigger on the scope channel that is connected to the TX, and watch the RX signal shift as you bring a target close to the coil. It is then easy to see that the phase-shift of the target is dependent on depth.

Indeed, and real goal would be to achieve less phase shifts, influenced by depth rises. Same old problem; some medium sized iron at greater depths will be detected as "coloured" by many detectors not only TGSL in the soil especially.
TGSL has weak TX. Is it possiblle to overcome phase issue with stronger output? At least to expand accuracy at a bit greater depths... I think it is possiblle. Stronger output will expand accuracy and phase would be slightly shifted at greather depths than it is now. But stronger TX will cause many other problems, stabillity issue at first place...
Would be good to analyze disc circuitry at White's Eagle, XLT,MXT,M6 and DFX serie. Those are accurate up to some point and VDI shows real numbers, but after some point those do not showing any number, just undefined audio on deep detections.... So problem is not solved at those models but also those do not "claim" deep items as "coloured" or iron. Just producing audio at detection of those deep items. Smart done.

[Geo]

Yes it was last year. I made 12 devices using "Goldy" pcb. All works until today very good.
I rearranged new pcb than to suit enclosure i got than - CZ5 enclosure. Than i got 1265/66 enclosure and draw another pcb, than i got Gold Bug 2 enclosure and draw new one....than i got MD3009 and 3009a and draw another pcb...huuuh!
All this vould be voided if i had same type of enclosure from a very start.
But i didnt, so ...
But initially, "Goldy" was the very FIRST one we (Nakky,ApBerg and me) did using TGSL schematic - TGS without notch part.

No chatters and hums (at least not significant) on Goldy IF coil is made and nulled well. So i can only recommend it also as others, to be used.
Regards!

Hello Ivica Do you know if Roberts will be at belligrad at 7....8/11. I want to meet him
Please contact with him and tell me.
Regards

[Qiaozhi]

I'm not completely clear on this, .....

Simply monitor the output signal from the pre-amp relative to the TX signal. You will need a 2-channel scope to do this. Trigger on the scope channel that is connected to the TX, and watch the RX signal shift as you bring a target close to the coil. It is then easy to see that the phase-shift of the target is dependent on depth.

[Aziz]

Hi SB,

..
I was thinking maybe we could try just taking the ratio of the two DC voltages (V1 / V2) somehow. That's still pretty tricky in analog electronics probably. But the idea is that because the depth of the target would equally affect V1 and V2, but the phase would affect V1 and V2 differently, dividing them would remove the effect of depth and leave the effect of phase.
..
-SB

Indeed... analog division and multiplier is really complex one:
lV1 = ln(V1) (logarithmic amplifier)
lV2 = ln(V2) (logarithmic amplifier)
for division: tmp = lV1 - lV2 (subtracter)
for multiplying: tmp = lV1 + lV2 (adder)
Result: exp(tmp) (exponential back transformation, anti-logarithmic amplifier)

All these stages would add much noise to the signal. It is a cost effective feature. Of course, you can take multiplier and divider chips. They need often at least 12..18 V bipolar supply voltage. And they are very expensive. Doing these steps in digital manner is much cheaper!

Aziz

[simonbaker]

The problem with trying to display the target ID on a meter - especially with the TGSL, which is an analog detector - is that the phase-shift produced by the target is dependent on the distance from the coil. There is little point in providing a ferrous/non-ferrous indication, as the TGSL always eliminates ferrous targets when DISC is switched on. The main difficulty with making your own coils is adjusting them such that the DISC control provides minimum discrimination when turned fully left, and maximum discrimination when turned fully right. This is why the initial phase adjustment is so important. Otherwise the minimum setting could end up in the middle, for example.

I'm not completely clear on this, but I see it this way so far. Because TGSL is a "motion detector", the residual nulling signal creates a constant voltage that is removed by its bandpass filters. That's because when a moving target signal is detected, it is essentially added to the nulling signal and is really independent from it. I'll try to explain.

On an oscilloscope we may see a combined signal whose phase is dependent on the nulling residual and the target signal, but the TGSL does not really respond to the phase of the combined signal (null residue + target) because the bandpass filters remove the null residue part. So it really can measure the absolute phase of the target signal by itself. (Others may disagree with me but that's what the math seems to indicate).

In fact the TGSL detects the target signal twice -- by sending the received signal (null residue plus target) down two paths, in each path multiplying it by a square wave of the same frequency but carefully chosen phase. After multiplying, you get a "DC" voltage that tells you about the received signal. Because the target signal part is momentary (as we move the metal detector coil over the target), it really produces a low frequency pulse, say 1/8 to 1/2 second. That allows us to use a very low frequency bandpass filter to remove the constant voltage from the null residue signal and just let the target signal pulse through.

But back to the received signal where we multiply and make a DC voltage. On one path, the square wave is shifted in phase about 90 degrees from the other. The result is that the DC voltage that results will depend on the phase of the target signal as well as the amplitude.

If the target signal is in phase with one square wave, it will come through loud and clear, but the other channel will have zero response, and vice versa. If the target phase is between the two square waves, each channel will have a response. So you can basically compare the two responses and determine the phase of the target signal. As it turns out, different metals produce target signals of different phase, so determining phase is how we discriminate between them.

Practically, we don't actually compute phase. What we actually do is, with our descriminator knob, shift one of our square wave signals until all signals with less than a certain phase make a negative DC voltage, and all signals greater make a positive DC voltage. The other channel we leave alone. Then we feed both DC voltages to some comparators that provide a logical "AND" function, meaning they make a high signal only if both inputs are high. So only metals whose phase shift makes a positive DC voltage in both channels will make a high signal, which is used to trigger an audio tone.

Now back to the original question, displaying the phase on a meter. We have measured the target signal on two channels. But the complication is that the amplitude of the DC signal depends on the amplitude (depth) as well as phase of the original target signal from the RX coil. We want to ignore depth and just pay attention to phase. There is actually a mathematical way to compute phase of a signal if you know the two amplitudes of the DC signals from the two channels. To do an exact computation in analog electronics is too much bother for our nice simple TGSL circuit.

I was thinking maybe we could try just taking the ratio of the two DC voltages (V1 / V2) somehow. That's still pretty tricky in analog electronics probably. But the idea is that because the depth of the target would equally affect V1 and V2, but the phase would affect V1 and V2 differently, dividing them would remove the effect of depth and leave the effect of phase.

Well, that was a lot of wind, but that's the idea. Maybe there is a clever way to do it without using tons of circuitry. It's not important if the meter measures phase accurately, just so long as it shows different values for different phases, and is independent of depth. With the right circuitry, theoretically you could make it measure depth and ignore phase when you flip a switch. But don't expect much reliability -- targets in the real world are full of nasty treachery that can fool circuits a lot of the time.

Cheers,

-SB

[Qiaozhi]

I see the point...
By the way, I'm suffering from problems you mentioned on adjusting the coil. I'm looking for a minimum possible level at LF353 output. Would other methods be better for nulling coils?

There are two possible methods:

1. Initially adjust the coil overlap until the output of the pre-amp (LF353) is close to zero. Fix the main body of the coils at this point. Then do the final adjustment of the overlap to achieve a phase-shift of 200 degrees relative to the TX signal. You will need a 2-channel scope to do this.


2. Initially adjust the coil overlap, as before, and fix the main body of the coils. Then set the GEB control to mid-position, and monitor the output of the sample gate in the ground balance channel. This is located at the source pin of TR5, which is connected to C12. I am referring to the reference designators shown in the schematic of the gift pack. Adjust the final overlap to achieve as close to zero volts as possible at this point. Once this is setup correctly, the discrimination channel will work as expected, as it samples at 90 degrees to the GEB.

Method 2 is the best approach.

[xix]

The problem with trying to display the target ID on a meter - especially with the TGSL, which is an analog detector - is that the phase-shift produced by the target is dependent on the distance from the coil. There is little point in providing a ferrous/non-ferrous indication, as the TGSL always eliminates ferrous targets when DISC is switched on. The main difficulty with making your own coils is adjusting them such that the DISC control provides minimum discrimination when turned fully left, and maximum discrimination when turned fully right. This is why the initial phase adjustment is so important. Otherwise the minimum setting could end up in the middle, for example.

I see the point...
By the way, I'm suffering from problems you mentioned on adjusting the coil. I'm looking for a minimum possible level at LF353 output. Would other methods be better for nulling coils?

[Qiaozhi]

I think we'd need a "ratio" circuit that gave ratio of outputs of LM308s independent of amplitude.

Thanks Simonbaker.
What do you mean by ratio circuit? a comparator that measures the differences on LM308's ouput signal?
Cheers

The problem with trying to display the target ID on a meter - especially with the TGSL, which is an analog detector - is that the phase-shift produced by the target is dependent on the distance from the coil. There is little point in providing a ferrous/non-ferrous indication, as the TGSL always eliminates ferrous targets when DISC is switched on. The main difficulty with making your own coils is adjusting them such that the DISC control provides minimum discrimination when turned fully left, and maximum discrimination when turned fully right. This is why the initial phase adjustment is so important. Otherwise the minimum setting could end up in the middle, for example.

[xix]

I think we'd need a "ratio" circuit that gave ratio of outputs of LM308s independent of amplitude.

Thanks Simonbaker.
What do you mean by ratio circuit? a comparator that measures the differences on LM308's ouput signal?
Cheers

[simonbaker]

Thanks Unregistered.
My idea would be to get some kind of target evaluation without being always touching the button of discrimination level
Cheers

I think we'd need a "ratio" circuit that gave ratio of outputs of LM308s independent of amplitude.

[simonbaker]

Guys I trashed the damn board! I desoldered almost all valued components and I'm making new board for the TGS. Bolder traces, higher copper thickness, no ground plane..
(it could be the plane doing the nasty stuff around, I think I prefer the chatters for a starter)
--
I also needed some additional stuff (pots, diodes, etc) and had the chance to order few more ICs for testing so soon we will have BATTLES:

1. LF353 (metal can) vs LF353N (ST) vs LT1057 (LT) vs TL082 (TI)
2. LM393 (ST) vs LT1018 (LT)
3. LM308 (motorola) vs LT1008 (LT)
4. LM358 (ST) vs TL082 (TI) vs OPA2277 (BB-TI)

Funny thing is that the LF353 metal can looks old, perhaps 10 years old, taken from old russian TV Elektron
( and they are famous all around with the weight - more than 100 pounds, tons of parts I tell you ..)
Manifacturer logo looks like a triangle, can't recognize it.
We'll see how the Old timer works :P

PS: Check out the avatar I think it's the most appropriate!
Cheers

Hi Eclipse -

I was thinking of using your board because more spread out than Ivconic's I think; I have many bulky parts , probably need the extra space.

Question: Are all your parts pin-compatible with TGSL gift pack schematic parts, or are do we need to use special parts in places or reverse leads, etc?

Also: you were going to make a 2nd PCB layout, more simple; were you able to do that? Is that available to?

BTW: I have always wondered if power supply capacitor 220 uF C29 is on wrong side of LM7808 -- Qiaozhi seemed to think it should be on output, not input. It would be nice if you could make your layout so we could put it on either side of LM7808 (or both!).

Hope your second gen TGSL is coming along well.

-Regards

-SB

P.S. Is your layout file looking from top (component side) or bottom of board? I'm never sure without detailed checking pins.

P.P.S. Do you have any jumper wires on your board, or just traces? Is is single-sided?

-Thanks

[karlos x]

DD

ok firstly I will make this coil

0.30 mm wire. 235mm diameter OO coil.
RX=150w
TX=140w

See page #14 post 330/333/347

[xix]

in disc mode you don't pay attention to the knob, at any position it will reject iron

Thanks Unregistered.
My idea would be to get some kind of target evaluation without being always touching the button of discrimination level
Cheers