TESORO GOLDEN SABRE

[ivconic]

"...Ivconic - now go and buy a decent scope. .."

If this solve my problem than i'll first buy huge box of beer and honestly get "wet".....later comes scope and stuff...

But wait first to be sure...

[Qiaozhi]

"...Ivconic - now go and buy a decent scope. .."

If this solve my problem than i'll first buy huge box of beer and honestly get "wet".....later comes scope and stuff...

But wait first to be sure...

But the good thing about buying a scope is ... it's still there tomorrow!
With beer, you never buy it - you only rent it.

[ivconic]

Plain truth!

But after box of beer, my head can be used as pretty good scope at least day or two after...

[ivconic]

Intend to buy this one. Any suggestions...?

[Qiaozhi]

Intend to buy this one. Any suggestions...?

Don't really know. Never used one.

I notice that it only has one channel though, which would be a problem. How are you going to measure any phase relationships, such as TX versus RX, or sample pulse versus sync demod output?

The one good thing I like is the storage facility and the cheap price.
Have a look here -> http://www.maplin.co.uk/module.aspx?...doy=19m10#spec
There's a couple of videos as well, but the first one is crap. The presenter is so monotonic, that you almost fall asleep with disinterest. You can also download the complete manual.

[Qiaozhi]

You could always make your own.
http://www.chocbar.demon.co.uk/

[ivconic]

Good question. But i have limited budget for now. 2 channel scope will cost me much more money...

This one looks sharp tome;

http://www.chocbar.demon.co.uk/

But i took only skim look on it...Dont know if i can find all components for it?
Also need pc to be attached. Dont know?

If i find some 2 channel second hand than for sure i'll buy it...
But i dont like desktop devices any more.... Must be something handy and cheaper to suit our needs here?

[ivconic]

Now, this one is more like it !!! 'Beast" in small package! But with double price...
I have 10 days to rethink on this....

[ivconic]

AAAARRRRGGGHHHHHH!!!!!


Finally problem is SOLVED for real!!!!!!!
But i have to admit - without oscilloscope (even obsolete) i would never find out what was the real problem!!! Also i have to thank to all of you on great support and efforts involved here!

Problem WAS damn %&^%$#@%$^%$$@%$% 100pF capacitor C9 at LF353!!!
I bought 10 of those brand new from same supplier! Even checked each of those with capacitance meter!? Each showed 105-115pF on meter!!!
I would never have any doubts more on those.....but after all possible doubts i decided few hours ago to take oscilloscope probe and "trace" signal after each component....without much of a concept...And i founded it! Damn $%$% capacitor. Out of circuitry it is acting like good one. Included in circuitry it is not good at all. I simply replaced those with first came handy to me - ordinary ceramic capacitors....and it is working PERFECT!
Like Max stated; now i can adjust Sense at Maximum and Disc at minimum.......no chatters, no "beep's"....Calm and silent like stone!
Also in All Metal mode with Sense to Maximum....working PERFECT...no false signals at all!!!!
On coins depth remained same but on larger items...like Cola can depth (distance) raised for 30% more !!!! It can detect Cola can over 80cm in the air now, with 27cm coil. Havent checked yet distances with larger Eliptical coil 32cm...To tired...i'll continue tomorow with testing...
Now i can adjust everything by the book! GEB trimmer is now adjusted right in the middle...everything else same as Max described earlier...Huh!!!!

Damn local suppliers....thieves!


Again, people, thank you so very much for suggestions and efforts here!
Best regards!

[Geo]

Good

Ok. I found the problem. It was inside the coil (wrong connection). My coil is from Cl3 32cm with 6.2mH for Tx and 5mH for Rx.Frequency is 14.1Mhz. I don't made fine tune the Rx.... i only connected a 5n6 parallel with 15n. So i took 40cm for a 30mm coin..... 36...37co for 2Euro .......... 34...35cm for 1 euro and 28cm for 2cents. All measurements are in all metal mode with sens at full. I connected a LM386 for better audio (but ir wants something yet). Today i will connect the 5mH to the Tx and i will put a capacitor to make oscillator to work at 14Khz and i will fine tune the Rx. Also i will try the Discrimination mode and the notch.
I want to take 5...6cm more so to be near the XLT or GTI2500. Maybe a better coil is the solution, but the free time is another problem.
Bye

[Max]

Hello Frends.

Qiaozhi, in the past I had some problems with wire wound pots, when replaced by a 'normal' pot the problems were gone, can it be that there is an L function ?

Well made some screenshots, transmit sinus is 2 v p/p also the 353-1 is 2 v p/p for the r25 and r26 signals it is 0.2 v p/p ( I hope..... can be wrong )

First is LF353-1 then two from r25-q7 then two r26 q6

Ap

Hi Ap,
thanks for the good qualiry pictures. Last 4 are like what I have... but I haven't a sinus at pin1 of LF353. Are you sure you are sampling at pin1 ? I'm referring to the original schematic... as in the picture under the red circle.

It's strange if you have a perfect sinus there and I haven't it.

1st picture is maybe the signal at output of preamp (pin 7) ?

My signal is a parabolic like in the picture I've posted... and has a superimposed sinusoidal damped signal.

Let me know.

Kind regards,
Max

[Max]

Ivconic, the reason that the pin 1 waveform is so out of control, is because you have removed the original GS notch level 10k potentiometer
that was directly paralled with the 100k discriminate pot. By removing the notch circuit, you have increased the gain of the opamp - at
the same time as you also increase the likleyhood of oscillation because of the higher feedback resistance.

Either change to a 10k Disc pot, or parallel a 10k fixed resistor across the 100k pot, and see what happens. It will very likely cause a different curve
to the Discrimination potentiometer effect (to be more like the original), but things should smooth out.

The LF353 is not a rail-to rail opamp. By having raised the circuit's gain, you have run out of dynamic headroom!
It feel stupid for not realizing this sooner.

Hi porkluvr,
you are right on this, I've checked and results from simulations are the same as I can see on scope... with some minor difference.

It's better adding a fixed resistor to modified schematics... cause , also, not all LF353 are the same out there.

I was thinking few days ago at something related to that...cause when I turn the notch pot, even with notch disabled by switch, I can ear differences on the audio... and that's cause of current flowing in.
But then I forget to investigate more on circuit about that...

I have all graphite pots, not wire-wound ones on TGS... and that's true that a modification must be made according original gain of LF353 half... you showed why. It's really important for stability.

Kind regards,
Max

[Max]

Finally problem is SOLVED for real!!!!!!!
But i have to admit - without oscilloscope (even obsolete) i would never find out what was the real problem!!! Also i have to thank to all of you on great support and efforts involved here!

Problem WAS damn %&^%$#@%$^%$$@%$% 100pF capacitor C9 at LF353!!!
I bought 10 of those brand new from same supplier! Even checked each of those with capacitance meter!? Each showed 105-115pF on meter!!!
I would never have any doubts more on those.....but after all possible doubts i decided few hours ago to take oscilloscope probe and "trace" signal after each component....without much of a concept...And i founded it! Damn $%$% capacitor. Out of circuitry it is acting like good one. Included in circuitry it is not good at all. I simply replaced those with first came handy to me - ordinary ceramic capacitors....and it is working PERFECT!
Like Max stated; now i can adjust Sense at Maximum and Disc at minimum.......no chatters, no "beep's"....Calm and silent like stone!
Also in All Metal mode with Sense to Maximum....working PERFECT...no false signals at all!!!!
On coins depth remained same but on larger items...like Cola can depth (distance) raised for 30% more !!!! It can detect Cola can over 80cm in the air now, with 27cm coil. Havent checked yet distances with larger Eliptical coil 32cm...To tired...i'll continue tomorow with testing...
Now i can adjust everything by the book! GEB trimmer is now adjusted right in the middle...everything else same as Max described earlier...Huh!!!!

Damn local suppliers....thieves!


Again, people, thank you so very much for suggestions and efforts here!
Best regards!

Hi,
very good Ivconic... you solved the big problem! Congratulations!

I think you need also the 10K fixed resistor to have much safer operations like porkluvr showed by simulation.

When you rotate the GEB trimpot you could find positions where bleeping appears... look for that over the point you can null for ferrite. Seems this is the greater instability area ... and that's truly important know what's behaviour there cause you have to use detector in that zone on real soil.

What about wrong cap ? Isn't it ceramic (my capacitor there is ceramic)
What was the problem with it ?

Please explain better.

Kind regards,
Max

[Max]

Ok. I found the problem. It was inside the coil (wrong connection). My coil is from Cl3 32cm with 6.2mH for Tx and 5mH for Rx.Frequency is 14.1Mhz. I don't made fine tune the Rx.... i only connected a 5n6 parallel with 15n. So i took 40cm for a 30mm coin..... 36...37co for 2Euro .......... 34...35cm for 1 euro and 28cm for 2cents. All measurements are in all metal mode with sens at full. I connected a LM386 for better audio (but ir wants something yet). Today i will connect the 5mH to the Tx and i will put a capacitor to make oscillator to work at 14Khz and i will fine tune the Rx. Also i will try the Discrimination mode and the notch.
I want to take 5...6cm more so to be near the XLT or GTI2500. Maybe a better coil is the solution, but the free time is another problem.
Bye

Hi Geo,
fine. If you tune coil and it's 32cm diameter you'll get more depth I think.

As you can see the TGS circuit is good for depth with small things... much like some PI detectors with small coils!

My only thoughts are about sensitivity to very small objects like 1eur-cent sized things... maybe the 32cm coil would detect them at lower distance cause of field shape/density.

Let me know.

Kind regards,
Max

[Max]

Hi,
about scope... here frequencies are so low that one could also look for products like:

http://www.virtins.com/

Kind of sound card scopes , func gen and spectrum analyzers...

or just use some homemade adapter for sound card directly....

Of course, there are cheap portable digital scopes for less than 100eur now... but they are really limited too (2MHz analog BW) and so I don't think that's a good choice preferring one instead of sound card for small BF frequency signals monitoring.

Anyway, if have to buy a cheap, portable one I'll choose one with at least 10-12MHz BW (or better 20MHz) not less cause otherwise is wasted money only...

I like very much portable 100MHz tektronics ... but they aren't cheap... so for that small things they aren't the right choice.

Kind regards,
Max