TESORO GOLDEN SABRE

[Fred]

Also, the FET is for amplitude stabilization, not frequency.

Ok,
As the zener was making changes in frequency, i thought some auto-frequency stabilization could occur at the same time.

The idea is maybe I have some metallic stuff on clothes and then breathing I move that and so device "see" my buttons move!

Max,
I don´t know from where you take your breath, but where i have metallic buttons it sures don´t move much when i breath.
Regards,
Fred.

[Geo]

Ok seems you are right Quiaozhi; "..The Clapp oscillator is a Colpitts oscillator with an additional capacitor placed in series with the inductor..."
I practically ejected fet stabilisation cose alredy worked several months with some of my TGSL's on various terrains, under real conditions and saw it in action. Fet stage serves for nothing really here.Better to fine readjust resistances arround 2N2907.

Max so you were "russian" once, and now you are NOT !
Reffereing TX output power....

Seriously, i do like russian projects in general, just dont have a clue why they insist on so much power there? Other hand TGS has low power TX so i was thinking to achieve something between russian and original Tesoro approach - to power up a bit more TX and see what will happen...
I like TX stage, KT315 posted in Sturm. Only if he can come here and tell us what is the amplitude measured there at that detector TX...
KT315 are you here?

Hi Ivica.... How are you
On 7 or 8 November i will come again to Beogrand (i think is the same with Beligrand). Do you have the same phone as last year ???
I will try to call you
Regards

[simonbaker]

Ok seems you are right Quiaozhi; "..The Clapp oscillator is a Colpitts oscillator with an additional capacitor placed in series with the inductor..."
I practically ejected fet stabilisation cose alredy worked several months with some of my TGSL's on various terrains, under real conditions and saw it in action. Fet stage serves for nothing really here.Better to fine readjust resistances arround 2N2907.

Max so you were "russian" once, and now you are NOT !
Reffereing TX output power....

Seriously, i do like russian projects in general, just dont have a clue why they insist on so much power there? Other hand TGS has low power TX so i was thinking to achieve something between russian and original Tesoro approach - to power up a bit more TX and see what will happen...
I like TX stage, KT315 posted in Sturm. Only if he can come here and tell us what is the amplitude measured there at that detector TX...
KT315 are you here?

Audio proportional to depth is tricky. Look at dynamic range of signals. You need super logarithmic amp. TGSL tries for that with diodes in feedback path of gain-filter op amps. But because of comparators, serves mainly as overload control I think.

Comparators are big reason audio not proportional -- they are just on or off (except for tiny linear region). So comparators at end blow away much of the idea of proportional audio.

Well, not completely! Remember that "hysteresis" positive feedback resistor after the comparators? That actually does feed forward a signal from the LM308 to the LM358 stage. When the gain and threshold of the LM358 are set just right, the output of the LM308 rides on top of the square wave of the comparitors. It does provide some proportional audio to the speaker. But you may not see it unless resistors just right on LM358. I will return to this in a moment.

Question is: do we really want proportional audio, or just better audio? Proportional audio means weak signals very faint. What good is that? In some ways it is better to make all signals loud until they break up because of noise. When break up, you know there is no more depth possible, noise has overcome signal. If proportional, you always wonder: should I turn up the volume? I think maybe good compromise is: Have loud signal for shallow targets. As get deeper, reduce until medium signal. Keep medium until signal breaks up due to noise.

A real problem is that deep signals can make a very short pulse because there is always a threshold, and small signals sometimes "peek" over it. Short pulse directly amplified will make click in speaker. Right now I don't see much solution to short pulse other than a little astable hold. You want just enough to make short distinct beep, but shorter than shallower targets. I think that can be achieved. However, noise makes short pulses also, so you must trust your sensitivity threshold is set right.

Back to our TGSL audio stage, LM358 and Darlington. The comparator output is -5 to 8, but because of the diode and feedforward resistor, it is clipped at LM308 output (ground channel), which is ground plus signal. So input to LM358 is essentially ground + LM308 output signal. (Actually, the LM308 output is logarithmically compressed by the diode I think -- that can be adjusted by some resistors).

Now Darlington is referenced to ground, so it ignores anything negative. This is where it gets complicated how to set gain/threshold resistors for LM358. You have to decide what you want. If you set them correctly, you can get a pretty desirable audio signal which is a constant square pulse with a proportional signal added. It should mean that as signal gets weaker, your audio goes down but never below the level of the square pulse.

I think though that there is a difficulty if signal gets into linear region of comparators. The audio could cut out completely. So we tinker with the resistors to get some audio, and then ruin the balanced design. I am hoping there is a modification that will work in both cases.

One more thing while spending words here: the capacitors have a big effect on short pulses. They low-pass filter them and keep them below the threshold of the Darlington (depending on how you tinkered with the resistors). I am not sure they are set best for the kind of deep detecting we want.

A final last thought: so far, TGSL looks like beautiful simple design, especially good for fast recovery uses, like for hunting trashy areas, small targets, and using smaller coil. But we want it to work for deep targets. I personally feel the most important mod would be to make it a slower response circuit, and give up hunting trashy areas and small targets. I am studying this, but hard to do well and keep it simple. I think an assymetric circuit that has slow response with special quick recovery trigger after pulse crosses zero on return might work interesting, but no clean design yet!

Will keep working,

Regards,

-SB

[ivconic]

Ok seems you are right Quiaozhi; "..The Clapp oscillator is a Colpitts oscillator with an additional capacitor placed in series with the inductor..."
I practically ejected fet stabilisation cose alredy worked several months with some of my TGSL's on various terrains, under real conditions and saw it in action. Fet stage serves for nothing really here.Better to fine readjust resistances arround 2N2907.

Max so you were "russian" once, and now you are NOT !
Reffereing TX output power....

Seriously, i do like russian projects in general, just dont have a clue why they insist on so much power there? Other hand TGS has low power TX so i was thinking to achieve something between russian and original Tesoro approach - to power up a bit more TX and see what will happen...
I like TX stage, KT315 posted in Sturm. Only if he can come here and tell us what is the amplitude measured there at that detector TX...
KT315 are you here?

[Max]

Any fluctuation in TX power will have a minuscule effect on the received signal. Remember that you need to increase the TX power by 64x to double detection distance.
Also, the FET is for amplitude stabilization, not frequency.

Hi,
yes, right, 64 times power for just double the received signal so the distance of detection (well if noise stay the same).

2^3 x 2^3 ... cause need 2^3 power loss to the target, and 2^3 power loss from target back to rx coil.

Some time ago I made a dummy test using not such great power just about 10times and found a thing....device sound when I breath!

So I can make it silent just if stop breathing...

The idea is maybe I have some metallic stuff on clothes and then breathing I move that and so device "see" my buttons move!

I sure will never want such monster power of 64x on real soil...would be a real pain in the *** !

Kind regards,
Max

[Qiaozhi]

Hi Qiaozhi,
The GEB channel may handle the ground effect, but what about decreased range (if amplitude TX decrease) and frequency drift due to presence of ground and / or metal, that this fet circuit could ?
Regards,
Fred.

Any fluctuation in TX power will have a minuscule effect on the received signal. Remember that you need to increase the TX power by 64x to double detection distance.
Also, the FET is for amplitude stabilization, not frequency.

[Fred]

Secondly, fluctuations in TX amplitude, due to ground effect, are already handled by the GEB channel. A straightforward Colpitts osc, like the one Max posted, should do the job. And yes - it is a Colpitts, not a Clapp.

Hi Qiaozhi,
The GEB channel may handle the ground effect, but what about decreased range (if amplitude TX decrease) and frequency drift due to presence of ground and / or metal, that this fet circuit could ?
Regards,
Fred.

[Qiaozhi]

Whatever....i am not using fet part anymore. Of course base of 2N2907 goes via 47K to gnd. I get full 16vpp at collector.
With or without fet part i havent noticed any differences in behavior so far.
I do void fet part just for reason to save some space on pcb, no other special reason...

Other question here is interesting and possibly very important; threshold part? Original setup from first TGS posted here is without any trimmer just with fixed values. On one of my pcbs i included trimm for threshold and gained no benefit form it...
So at next pcbs i omitted it again.
Audio path is an issue here and must be reconsidered and modded. I tried many times and yet not satisfied..

The TX circuit in the TGSL is an amplitude-stabilized Colpitts oscillator. The purpose of the feedback via the FET is to keep the amplitude constant. In practice I do not think there is any real advantage to using this circuit. Firstly the +8V power rail is derived from the LM7808, which provides a regulated output. Note - that there is a 220uF on the input to the LM7808, but there should also be one on the output. If you want to conserve space on the PCB, then simply move the existing 220uF cap. It's not needed on the input anyway.
Secondly, fluctuations in TX amplitude, due to ground effect, are already handled by the GEB channel. A straightforward Colpitts osc, like the one Max posted, should do the job. And yes - it is a Colpitts, not a Clapp.

[ivconic]

Hi,
yes, I think that's the good way to keep everything powerful and stable, with good linearity of sinus.

The colpitts are easy but when doing at these levels of tuning is better tune also that stuff.

Kind regards,
Max

This looks rather more like Klapp (or Clapp ???) oscillator - not a Colpitts...

[ivconic]

I am also waiting some more ideas to occur, to adapt this pcb further, so once i make it, i want to change few more things than just TX amplitude and shape....
I done 28 TGSL's so far....kind a tired of repeating same old thing again and again....
So next MUST be pretty different.
Sooner or later i will face KT315's oftenly repeated attitude and remarks about "old and obsolete" stuff. Although i dont agree with it at all. But KT315 is right at some point, we must do something major at TGSL...

[Max]

I think you have right, Max!
I would rather adjust resistors there than to keep fet stage.
I was thinking to put trimmers instead base and emitter resistors and to adjust those using scope.
It was my idea from long time ago...i am just to lazy to do things faster than usually do...

Already adapted pcb draw, but dont have time to make it right now.Will be ready in a week or two...

Hi,
yes, I think that's the good way to keep everything powerful and stable, with good linearity of sinus.

The colpitts are easy but when doing at these levels of tuning is better tune also that stuff.

Kind regards,
Max

[ivconic]

I think you have right, Max!
I would rather adjust resistors there than to keep fet stage.
I was thinking to put trimmers instead base and emitter resistors and to adjust those using scope.
It was my idea from long time ago...i am just to lazy to do things faster than usually do...

Already adapted pcb draw, but dont have time to make it right now.Will be ready in a week or two...

[Max]

Whatever....i am not using fet part anymore. Of course base of 2N2907 goes via 47K to gnd. I get full 16vpp at collector.
With or without fet part i havent noticed any differences in behavior so far.
I do void fet part just for reason to save some space on pcb, no other special reason...

Other question here is interesting and possibly very important; threshold part? Original setup from first TGS posted here is without any trimmer just with fixed values. On one of my pcbs i included trimm for threshold and gained no benefit form it...
So at next pcbs i omitted it again.
Audio path is an issue here and must be reconsidered and modded. I tried many times and yet not satisfied..

Hi,
I see...

Yesterday I tried with a BC557 instead of 2N2907... and no fet on my TGSL board.

Result was 15Vpp signal but distorted at top... who knows why ???

The BC557 I used was 250 as HFE so about an average pnp one.

Using the fet (a BF245B) the voltage drops with that stuff at 14.4Vpp BUT is much more linear and almost near to perfect sinus wave.

As reported before, the FET serves much to mantain amplitude stabilization BUT also linearity of the sinus wave.

Is linearity important ? Well... I saw also distorted signal giving good performances on air but not always, and on soil linearity I think is important cause of geb/disc implications.

I also know that just transistor osc is fine (I have bandidoII running fine) but components are different at it... look at picture, with that values I really get perfect sinus there.

I think that's maybe a good idea refine components at oscillator of TGS if wanna pull-out the fet and have good linearity.

Kind regards,
Max

[ivconic]

I did that long time ago, so as experimented with different values - no benefits.
Removing C24 and C25 seems does not change anything in audio, but removing C26 do affects it to become worse.
Heck is somewhere else. I guessed once and will repeat again; all the signal path is issue here. Possibly some low amplification. Guess they (at Tesoro) wanted to supress chatters also so whole design is adapted in that manner.
What we need is sort of "linear" amplification, one stage more, than some MPSA13 or whatever at the end. But signal at last LM358 is pretty awkward to be easy played with it. If you followed this thread from a start ,you probably remember dozen small modds i tried already, sheeesh, nothing helped much! Few times i used signal to switch something to produce audio, and it worked but not "linear". Audio was independent of target preferences. That is not what i want. I want audio to be directly dependant of a target, so you can hear depth and size. Tough...very tough.

[simonbaker]

Whatever....i am not using fet part anymore. Of course base of 2N2907 goes via 47K to gnd. I get full 16vpp at collector.
With or without fet part i havent noticed any differences in behavior so far.
I do void fet part just for reason to save some space on pcb, no other special reason...

Other question here is interesting and possibly very important; threshold part? Original setup from first TGS posted here is without any trimmer just with fixed values. On one of my pcbs i included trimm for threshold and gained no benefit form it...
So at next pcbs i omitted it again.
Audio path is an issue here and must be reconsidered and modded. I tried many times and yet not satisfied..

Regarding audio: can you remove three capacitors after comparators (i.e. C24, C25, C26) and tell us what the audio sounds like? It will probably increase chatter, but will reveal some clues.

Regards,

-SB