TGSL Experiments

[simonbaker]

Thanks Max.
The local supplier offers only P version of LF353. My TGSL working unstable with good nuled coil and that was reason why I start thinking about P mark on this IC. Now, there's noting left form me to do but to change all of 100p, 15p and 10p caps with multilayer ones and we will see.. Can I do smething more to get better stabillity?
Best Regards

1. Can you show dual trace oscilloscope pictures of LF353 pin 1 (discrimination) on one trace, with TX oscillator (J1-pin1) on other trace ?

2. Also dual trace picture of LF353 pin 7 (RX signal) one trace with TX oscillator other trace?

3. Please describe oscilloscope grid scale for each trace, time and voltage.

4. What is your TX oscillator voltage (J1-pin1) peak-to-peak voltage?

5. What are voltages on .22uF caps C12 and C15?

6. Look at JFet driver pulses (output of LM393 U102, pins 1 and 7) for discrimination and ground channel while moving pots. Do the pulses stay square, or do they break up into smaller pulses?

7. What are RX and TX coil inductance and resistance?

8. What is TX oscillator frequency?

9. Is it unstable outdoors?

Regards,

-SB

[Ultimate_Haze]

Where are you using BF245C and PN4393? Are you sure you measure freq correctly?

I dont have J107 so for FET I use BF245C.I have measured freq. twice!So I am shore.


I have the same problem -- easy to make detector that works around 20 cm, but I have not achieved 30+.

I am trying to study each part to understand. The experienced people say "coil", so probably that is the answer -- but what makes one coil wrong, another right? I want to study and see. So I'm making various coils. It will take some time.
I am interested in same)))
One difficulty I have is electrical noise inside house. Final test must be outside away from power wires, with sensitivity pot turned most sensitive.
Question: when you use outside and turn sensitivity to most sensitive, do you hear "chatter", or is it quiet?

Exacly same.20cm no problem.But 30+.....Still havent test this outside.When here/in house/with sens at max,with some coil no cheeters at all.With some cheeters even under half sens.
2. RX coil resistance -- if too low, it may pick up extra noise at resonant frequency. If too high, reduces gain. Your value might be a little high, try slightly heavier wire to get around 20 ohms???? Who knows, it is something to experiment with.
I will make some more tests according your advices.

[simonbaker]

I dont have J107 so for FET I use BF245C.I have measured freq. twice!So I am shore.
.

Where are you measuring frequency? At coil or at JFet gate?

JFets in synchronous detector should not change frequency of oscillator at all! Can you explain some more?

If you measure freq at JFet gates (in synchronous detector), sometimes the square pulse at JFet gate can become "broken" into many and look like higher freq. That can happen for certain reasons.

Which schematic/PCB did you build? TGSL Final? I assume you do not have JFet in oscillator, is that correct?

Do you have an oscilloscope? There are many waveforms I am curious about.

I want to understand why some coils make "chatters", not just throw them away. It would be good to take measurements with the coil that "chatters". Especially, what are the voltages at capacitors C12 and C15.

I would like to try to analyze this if you have the patience.

Regards,

-SB

[Ultimate_Haze]

Where are you measuring frequency? At coil or at JFet gate?
I were measuring at coil.
JFets in synchronous detector should not change frequency of oscillator at all! Can you explain some more?
Now BF245 JFet are soldered back.
If you measure freq at JFet gates (in synchronous detector), sometimes the square pulse at JFet gate can become "broken" into many and look like higher freq. That can happen for certain reasons.
I can do the same again and check.
Which schematic/PCB did you build? TGSL Final? I assume you do not have JFet in oscillator, is that correct?
Yes, TGSL final.No JFet in oscillator
Do you have an oscilloscope? There are many waveforms I am curious about.
I can find.Please ask but step buy step.I will have to upload pictures too.
I want to understand why some coils make "chatters", not just throw them away. It would be good to take measurements with the coil that "chatters". Especially, what are the voltages at capacitors C12 and C15.
I am interested in same matter.
I would like to try to analyze this if you have the patience.
Yes,I have.Lets give it a try.

[simonbaker]

Where are you using BF245C and PN4393? Are you sure you measure freq correctly?

I dont have J107 so for FET I use BF245C.I have measured freq. twice!So I am shore.


I have the same problem -- easy to make detector that works around 20 cm, but I have not achieved 30+.

I am trying to study each part to understand. The experienced people say "coil", so probably that is the answer -- but what makes one coil wrong, another right? I want to study and see. So I'm making various coils. It will take some time.
I am interested in same)))
One difficulty I have is electrical noise inside house. Final test must be outside away from power wires, with sensitivity pot turned most sensitive.
Question: when you use outside and turn sensitivity to most sensitive, do you hear "chatter", or is it quiet?

Exacly same.20cm no problem.But 30+.....Still havent test this outside.When here/in house/with sens at max,with some coil no cheeters at all.With some cheeters even under half sens.
2. RX coil resistance -- if too low, it may pick up extra noise at resonant frequency. If too high, reduces gain. Your value might be a little high, try slightly heavier wire to get around 20 ohms???? Who knows, it is something to experiment with.
I will make some more tests according your advices.

One more thought....

Very important to test outdoors. The coil that chatters indoors may be the best coil outdoors, deepest and most sensitive! So retest all coils outdoors.

Regards,

-SB

[simonbaker]

Where are you measuring frequency? At coil or at JFet gate?
I were measuring at coil.
JFets in synchronous detector should not change frequency of oscillator at all! Can you explain some more?
Now BF245 JFet are soldered back.
If you measure freq at JFet gates (in synchronous detector), sometimes the square pulse at JFet gate can become "broken" into many and look like higher freq. That can happen for certain reasons.
I can do the same again and check.
Which schematic/PCB did you build? TGSL Final? I assume you do not have JFet in oscillator, is that correct?
Yes, TGSL final.No JFet in oscillator
Do you have an oscilloscope? There are many waveforms I am curious about.
I can find.Please ask but step buy step.I will have to upload pictures too.
I want to understand why some coils make "chatters", not just throw them away. It would be good to take measurements with the coil that "chatters". Especially, what are the voltages at capacitors C12 and C15.
I am interested in same matter.
I would like to try to analyze this if you have the patience.
Yes,I have.Lets give it a try.

Thanks for those details.

When you get an oscilloscope let me know. It is important to have dual trace. If only single trace, then must have external trigger, but dual trace much better.

Regards,

-SB

[Ultimate_Haze]

Hi,
Simonbaker.
I have made some more tests.
Its looks like I found a clue.When measured from TX frequency is around 14.1 on my last coil.Same story-low sens.I decide to take your advice and monitor the gates of JFets.On G of TR5 I have same frequency like in TX.But on G of TR4 I have 26,7!!!Hum.Conected older coils same story.So mistake must be there.Any sugestions?

[simonbaker]

Hi,
Simonbaker.
I have made some more tests.
Its looks like I found a clue.When measured from TX frequency is around 14.1 on my last coil.Same story-low sens.I decide to take your advice and monitor the gates of JFets.On G of TR5 I have same frequency like in TX.But on G of TR4 I have 26,7!!!Hum.Conected older coils same story.So mistake must be there.Any sugestions?

I have an idea but need scope pics to confirm. The problem (that I have experienced) is that the oscillator voltage is so high it is exceeding rails of LF353 and making trouble there. Sometimes you can get away with it with certain LF353 and capacitors and maybe if TX coil has higher resistance, but I believe normally it can cause trouble -- not everyone agrees with me.

To analyze without scope, try connecting 100k or bigger potentiometer across resistor R17 (feedback resistor on LF353 of discrim circuit). While checking frequency on G of TR4, turn potentiometer to make resistance smaller. See if frequency drops to 14 k.

If that doesn't work, other test requires cut wire and insert potentiometer.

Cut wire from TX coil J1 that goes to C9 and C10. Insert potentiometer (50 K is good choice) to ground so you can lower the voltage coming from oscillator to C9 and C10. Do same test as before -- turn potentiometer to lower voltage and see if frequency at gate of TR4 stabilizes to same as TX oscillator.

Eventually it is important to look at signal at LF353 pin 1 with scope to make sure it is clean.

If this is the problem, I am still analyzing for good way to fix with my circuits. Maybe certain TX coil no problem, but I think should be possible with any TX coil, that is my goal.

Regards,

-SB

[Qiaozhi]

I have an idea but need scope pics to confirm. The problem (that I have experienced) is that the oscillator voltage is so high it is exceeding rails of LF353 and making trouble there.

Maybe it's because you've removed the original amplitude stabilization circuitry from the TX circuit.

[simonbaker]

Maybe it's because you've removed the original amplitude stabilization circuitry from the TX circuit.

Correct! but that is how the TGSL Final version is designed. I feel additional modification may be needed in some cases even though many people seem to be successful with it as is. If you can get away with it, bigger TX signal should help depth. There is a nonlinear "bump" issue also that can affect the discrimination control, so looking at it from several angles.

-SB

[ivconic]

Problems with simulators and calculators (just comparsion) is in fact that you can not simulate and predict real signal behavior in real soil conditions. Especially when we talk about coil. Ever since first device i made without TX stabilisation parts i noticed excellent behavior without any issues on real fields. No issues with TX at all. Trust me or not, but that is the truth. Actually i havent noticed any differences between previous handmade with TX stabilisation included and next one without it. In both cases i have scoped TX vaweforms. Small "notch" you mentioned is present in both cases. Same amplitudes, same shapes...same behavior. Seems stabilisation circuitry is there to stay and "do nothing" in 99% of cases. Just in some rare case when something very strange happen with signal, it is there to cut amplitude or whatever....So far i havent case to see that part in action. With or without it...TGSL is acting very same. No differences at all.
I am not talking about experiences gained on only one or two handmades. I am talking about experiences gained with 34 handmades made so far. Among those 34 devices, ihad chance to keep and work with 5-6 so far for longer period, you may say month or two keeping it and working with it on plenty terrains. Lot of finds and a lot of "in vivo" tests and checks.
Besides...we have Bandido with simillar concept and also without TX stabil. parts....Silver Sabre.....Diablo Gold Daemon...Lobo....
I presume must be something in original coils which makes differences. Beleive me or not...i made 34 devices so far and havent yet seen neither one original TGS coil! Looking forward to get one sooner or later and to examine it in details...

[simonbaker]

Problems with simulators and calculators (just comparsion) is in fact that you can not simulate and predict real signal behavior in real soil conditions. Especially when we talk about coil. Ever since first device i made without TX stabilisation parts i noticed excellent behavior without any issues on real fields. No issues with TX at all. Trust me or not, but that is the truth. Actually i havent noticed any differences between previous handmade with TX stabilisation included and next one without it. In both cases i have scoped TX vaweforms. Small "notch" you mentioned is present in both cases. Same amplitudes, same shapes...same behavior. Seems stabilisation circuitry is there to stay and "do nothing" in 99% of cases. Just in some rare case when something very strange happen with signal, it is there to cut amplitude or whatever....So far i havent case to see that part in action. With or without it...TGSL is acting very same. No differences at all.
I am not talking about experiences gained on only one or two handmades. I am talking about experiences gained with 34 handmades made so far. Among those 34 devices, ihad chance to keep and work with 5-6 so far for longer period, you may say month or two keeping it and working with it on plenty terrains. Lot of finds and a lot of "in vivo" tests and checks.
Besides...we have Bandido with simillar concept and also without TX stabil. parts....Silver Sabre.....Diablo Gold Daemon...Lobo....
I presume must be something in original coils which makes differences. Beleive me or not...i made 34 devices so far and havent yet seen neither one original TGS coil! Looking forward to get one sooner or later and to examine it in details...

I believe you completely that it works great -- but I don't know why!

I just see what I see with my built MDs (only two yet). If I take out JFet from oscillator, I can get trouble in LF353 - garbage out. Maybe if I put it over soil, it will behave -- you have a point. I'm always on bench.

I agree difference could be coils. I use heavy wire, get extra big oscillations because low resistance. So now I am making TX coil with thinner wire, we'll see.

As I say many times, I'm not worried about it (yet), just very interested to understand. I want to keep trying using thick wire (I've got 7 pounds of 24 gauge -- it makes a good barbell) because I believe it can get more depth and use less batteries. So maybe I'll need a "little mod" to make it behave.

Simulators can't replace real circuit, but when I see same problem in real circuit and simulator... I get interested.

So same old story, but I hope more interesting than annoying.

Regards,

-SB

[simonbaker]

Molzar TGS

Hi Molzar, if you see this:

I'm not sure if asked before, but:

On Tesoro TGS you have, can you look at output of LM393 comparators that get input from LM308. Are there any resistors (like 4k7 resistor) on the output before the outputs come together, or are the outputs directly connected together?

There was one schematic that had resistors, but most don't. I just want to confirm how Tesoro did it.

Regards,

-SB

[Ultimate_Haze]

Some pictures:

[ivconic]

I believe you completely that it works great -- but I don't know why!

I just see what I see with my built MDs (only two yet). If I take out JFet from oscillator, I can get trouble in LF353 - garbage out. Maybe if I put it over soil, it will behave -- you have a point. I'm always on bench.

I agree difference could be coils. I use heavy wire, get extra big oscillations because low resistance. So now I am making TX coil with thinner wire, we'll see.

As I say many times, I'm not worried about it (yet), just very interested to understand. I want to keep trying using thick wire (I've got 7 pounds of 24 gauge -- it makes a good barbell) because I believe it can get more depth and use less batteries. So maybe I'll need a "little mod" to make it behave.

Simulators can't replace real circuit, but when I see same problem in real circuit and simulator... I get interested.

So same old story, but I hope more interesting than annoying.

Regards,

-SB

No, this will not be a case here. If coil acts bad in air (in workshop) than it will act bad on real soil for sure. No doubts. Good and proper coils are acting good in both case.
Yet, your way of thinking is right to me. I tend to agree. Stabilisaton part (if that was its original role after all) is also very interesting to me. But if you analyze it a bit detailed, you will found out that base of 2N2907 is always coupled to ground via 47K. Fet's S and D are "shorted" in 99% of cases. Just when something happens strange, fet gets a signal to G and than S and D "opens" and switch 2N2907 base from 47K to 330K+47K to ground. So it acts actually as simple, ordinary switch ; but conditioned with G components (48,749,100K,0.22). So...i simply removed those and left only 47K to ground.
I guess all your "problems" are coming from inproper wire.
For a test...you can add resistor in serie with TX coil and see what will happen...