TESORO GOLDEN SABRE

[Dennis the Mennis]

I wound a new coil, this time very carefully and with thicker wire (0,4mm i guess) and with exactly 6,5mH (+/- 2,5% precision from multimeter) and now I get an awesome sinus with a bump and 11V AC !

I unwounded the old coil and it seems like the glue bit the insulation away and worked like some kind of capacitor without causing a short circuit. I will never use glue again.

Now I just need to find more wire for the second one and see how sensitivity goes, but I'm very confident.

Hi akademiker ,

Didn't you mixed up the bottle of acid and the bottle of glue ?

If you find enough wire for the Rx coil you also can try them without / before shielding for testpurposes.

I'm aware that the coils must be shielded for field operation but :

- see the big difference in phase shift when nulling compared to shielded coils ( at least for me and it seems that Mullihaka has the same problem ) http://www.geotech1.com/forums/showt...744#post117744

- Same for the residual voltage : from a few millivolts to volts

These are my observations at this time ...

Still my question remains : what is there to gain with different types of shielding
Perhaps a greater distance between shield and coil ?

Today I've stripped a vga cable with (I think) mylar shielding inside for my next experiment

Good luck with your coils

regards

Dennis the Mennis

[akademiker]

I wound a new coil, this time very carefully and with thicker wire (0,4mm i guess) and with exactly 6,5mH (+/- 2,5% precision from multimeter) and now I get an awesome sinus with a bump and 11V AC !

I unwounded the old coil and it seems like the glue bit the insulation away and worked like some kind of capacitor without causing a short circuit. I will never use glue again.

Now I just need to find more wire for the second one and see how sensitivity goes, but I'm very confident.

[simonbaker]

Hi Simon ,

What material did you use as shield for the coils ?

I've tried ordinary Al. kitchen foil (which should work) in several kinds of thickness but the biggest problem after shielding for me seems that I can't reach the desired 20 degrees when nulling (perhaps 40degrees and more ), and if I can the residual voltage is very high ( > 1,5v / 2v ).
But I had one time with these coils a great detection depth but I can't duplicate that anymore.
I have also a set of unshielded coils for test purposes under construction and these seem to be pretty 'ideal':

- when nulling there is no phase shift - remains at about 20 degrees at all times
- the residual voltage is extreme low , even at pin7 LF353 ( the nulling - /residual voltage at pin 7 LF353 does not affect the noise at the outputs of the LM308's , my typical noise is about 30/40 mV which is a little on the high side ? )


Perhaps when Akademiker makes a new set of coils he can test it also without shielding and see if he has the same experience as I did.

Is there something to gain the way the shielding is made ?


regards ,

Dennis the Mennis

ps have a nice vacation

Hi DtM:

My latest belief is: don't worry about the null phase due to the foil shield, or the high voltage. Try to null same as before -- find the minimum, then shift coils slightly further together (20% - 30% increased voltage?).

Then check to make sure voltage on C12 and C15 are not less than -.5 volts over the range of the DISC pot and GB pot range. Actually, for GB pot, only matters where you set for ground balance. If they are less than -.5 volts, I think it would be wise to shift the coils to change the voltage.

It think such coils should work OK. It may be something else that is causing reduced air depth -- particularly EMI noise! Hike to the mountains.

My last coil I used Scotch aluminum tape -- similar to kitchen foil in thickness or slightly thicker. dfbowers says he uses mylar like those "space blankets" for emergency warmth. He says don't wrap shield too close to coil, better to have a layer of tape or something underneath.

I do have a question whether shields make a phase shift that can "add in" to make a false minimum, but I actually think (hope) it is very close to the same minimum position as no shield. It depends on exact signal added by shield. Difficult to test, but maybe someone can design a test: null position, shielded vs. unshielded.

I'll enjoy the vacation - rain, fallen leaves, or jet lag regardless!

Cheers,

-SB

[Dennis the Mennis]

Coil shielding

Ok -- your scope photos looked like 9 kHz freq, consistent with 58 nF. Does your scope agree with your frequency meter?

I once glued a coil with Elmers white glue (water-based glue), and it seemed my coil lost something. I wonder...

I agree it doesn't seem like short circuit. Maybe some crazy physics going on. I'm curious. I wonder if water molecules in glue are causing a large damping effect (well, it is "damp" ) because they are dipoles flipping around...

A good physics/chemistry puzzle.

If you glue coil again, first test before gluing, then again after gluing.

Regards,

-SB

Hi Simon ,

What material did you use as shield for the coils ?

I've tried ordinary Al. kitchen foil (which should work) in several kinds of thickness but the biggest problem after shielding for me seems that I can't reach the desired 20 degrees when nulling (perhaps 40degrees and more ), and if I can the residual voltage is very high ( > 1,5v / 2v ).
But I had one time with these coils a great detection depth but I can't duplicate that anymore.
I have also a set of unshielded coils for test purposes under construction and these seem to be pretty 'ideal':

- when nulling there is no phase shift - remains at about 20 degrees at all times
- the residual voltage is extreme low , even at pin7 LF353 ( the nulling - /residual voltage at pin 7 LF353 does not affect the noise at the outputs of the LM308's , my typical noise is about 30/40 mV which is a little on the high side ? )


Perhaps when Akademiker makes a new set of coils he can test it also without shielding and see if he has the same experience as I did.

Is there something to gain the way the shielding is made ?


regards ,

Dennis the Mennis

ps have a nice vacation

[simonbaker]

Well...there can't be a short circuit inside, because inductivity and resistance are as expected, maybe the parasitic capacitance is just "eating" away the sinus? But even if the coil is at 11kHz this shouldn't drop the voltage as the coil is always in self resonance or does it?
Lets see if I can find some copper wire inside the giant coil in my broken CRT ^^
Tomorrow I will wind a new one and this time I will be most precise and after comparing I will solve the mystery of the broken coil ^^


"How do you measure parasitic capacitance?"

I calculated it, if I know f and L I know what C must be. Nono, the 38nF include C2, as C2 and Cparasitic are the cap in the oscillating circuit.
Some cheap allround glue "Tesa", maybe i used a little too much :S

Ok -- your scope photos looked like 9 kHz freq, consistent with 58 nF. Does your scope agree with your frequency meter?

I once glued a coil with Elmers white glue (water-based glue), and it seemed my coil lost something. I wonder...

I agree it doesn't seem like short circuit. Maybe some crazy physics going on. I'm curious. I wonder if water molecules in glue are causing a large damping effect (well, it is "damp" ) because they are dipoles flipping around...

A good physics/chemistry puzzle.

If you glue coil again, first test before gluing, then again after gluing.

Regards,

-SB

[akademiker]

Well...there can't be a short circuit inside, because inductivity and resistance are as expected, maybe the parasitic capacitance is just "eating" away the sinus? But even if the coil is at 11kHz this shouldn't drop the voltage as the coil is always in self resonance or does it?
Lets see if I can find some copper wire inside the giant coil in my broken CRT ^^
Tomorrow I will wind a new one and this time I will be most precise and after comparing I will solve the mystery of the broken coil ^^


"How do you measure parasitic capacitance?"

I calculated it, if I know f and L I know what C must be. Nono, the 38nF include C2, as C2 and Cparasitic are the cap in the oscillating circuit.
Some cheap allround glue "Tesa", maybe i used a little too much :S

[simonbaker]

Do you mean this bump?

My scope is pretty accurate, just recalibrated it with test signal. I measured the frequency with my multimeter, but now I know it shows false numbers. When I test the frequency, the wavelenght in scope gets shorter, so it measured too high frequencies all the time .

The TV inductor has around 11,6kHz at 7mH (27nF parasitic + real capacitance), TX around 11,3kHz (34nF parasitic + real capacitance) at 5,77mH and RX around 10,4kHz at 6,22mH (38nF parasitic + real capacitance) measured with scope. I guess the usb cable added even more parasitic capacitance
I guess I have to wind another coil <.<
I used some glue after I tied everything up with yarn and then i covered everything directly with alu tape.

That's the "bump"! Looks very normal.

How do you measure parasitic capacitance?

If we use 38 nF + 20 nF (C2, C1) for C and 5.77 mH for L in formula, I get 9016 kHz for oscillator freq, which is about same as I measured from your first scope photo of TX signal. Interesting. Although the photo of sync pulses seem more like 9.6 kHz.

Exactly what glue did you use?

Interesting about your frequency meter -- one of my meters interferes with the oscillator also, the other one doesn't. Maybe we need to add a big resistor, or a little JFet circuit or something to buffer it.

Tell us what you find if you take apart your TX coil.

Regards,

-SB

[simonbaker]

Hi ,

Or try to connect your Rx coil on the Tx circuit .
This saves you some time in winding another coil and it is another easy way to find out if the problem is in the coil or in the Tx part of your circuit.

You can also doublecheck and recalculate the values of your Rx coil given when connected to the Tx part.

http://www.whatcircuits.com/lc-resonance-frequency-calculator/

1. Enter desired f and C to calculate L (delete L before Calculate )

kind regards ,

Dennis the Mennis

Excellent ideas "Dennis"!

If you (akademiker) are convinced it is some defect in the TX coil, I would try unwinding it, just to see what it is!

-SB

[akademiker]

Do you mean this bump?

My scope is pretty accurate, just recalibrated it with test signal. I measured the frequency with my multimeter, but now I know it shows false numbers. When I test the frequency, the wavelenght in scope gets shorter, so it measured too high frequencies all the time .

The TV inductor has around 11,6kHz at 7mH (27nF parasitic + real capacitance), TX around 11,3kHz (34nF parasitic + real capacitance) at 5,77mH and RX around 10,4kHz at 6,22mH (38nF parasitic + real capacitance) measured with scope. I guess the usb cable added even more parasitic capacitance
I guess I have to wind another coil <.<
I used some glue after I tied everything up with yarn and then i covered everything directly with alu tape.

[Dennis the Mennis]

Nice job, it sounds like some problem in the TX coil.

Your "rail" voltages are perfectly normal.

Scope trace is best for measuring TX signal, AC meters are all different.

Usually people get around 16 V peak-to-peak, so 10 V AC may be correct. When it is working properly you will usually see a small "bump" distortion on the TX signal and it will be about 16 v pp. Can you post photo of oscillator voltage with TV inductor?


Your oscillator frequency with your TX coil seems to be around 9 kHz looking at your scope trace. This is too low for the inductance you measured (5.77 mH). Of course assuming your Oscope is accurate.

Because the TV inductor seems to work correctly, it seems something funny is in your TX coil.

19.6 ohms seems OK for TX coil. Can you check again anyway?

Do you have a frequency meter?

What is the measured frequency of the oscillator with your TX coil, and also with the TV inductor?

Do you have an inductance meter? What is the inductance of your TX coil?

Did you put any kind of glue on your TX coil?

One suspicion is that some windings have short-circuited in the TX coil. But this does not make sense to me because I would think it would make resistance lower and frequency higher. But who knows...

Because the TV inductor works OK (we need to be sure), it seems something is wrong in your TX coil, and that is a good mystery.

The best way to check is to wind another one.

Regards,

-SB

Hi ,

Or try to connect your Rx coil on the Tx circuit .
This saves you some time in winding another coil and it is another easy way to find out if the problem is in the coil or in the Tx part of your circuit.

You can also doublecheck and recalculate the values of your Rx coil given when connected to the Tx part.

http://www.whatcircuits.com/lc-resonance-frequency-calculator/

1. Enter desired f and C to calculate L (delete L before Calculate )

kind regards ,

Dennis the Mennis

[simonbaker]

V+ is 8V and V- is -6,7V.
Resistance from J1-1 to GND is around 15 Meg Ohms.
I connected an inductivity from an old tv around 7mH (3Ohms) and now it really shows 10V AC. Like it should be, right?
I disconnected everything and only connected the TX coil even without shielding with simple thick (1,5mm) wire directly to the oscillator but still only 4,8V AC. This drives me crazy.
In the Tuning &Troubleshooting thread Stefano's signal is around 8V AC, should it be in that range?

Nice job, it sounds like some problem in the TX coil.

Your "rail" voltages are perfectly normal.

Scope trace is best for measuring TX signal, AC meters are all different.

Usually people get around 16 V peak-to-peak, so 10 V AC may be correct. When it is working properly you will usually see a small "bump" distortion on the TX signal and it will be about 16 v pp. Can you post photo of oscillator voltage with TV inductor?


Your oscillator frequency with your TX coil seems to be around 9 kHz looking at your scope trace. This is too low for the inductance you measured (5.77 mH). Of course assuming your Oscope is accurate.

Because the TV inductor seems to work correctly, it seems something funny is in your TX coil.

19.6 ohms seems OK for TX coil. Can you check again anyway?

Do you have a frequency meter?

What is the measured frequency of the oscillator with your TX coil, and also with the TV inductor?

Do you have an inductance meter? What is the inductance of your TX coil?

Did you put any kind of glue on your TX coil?

One suspicion is that some windings have short-circuited in the TX coil. But this does not make sense to me because I would think it would make resistance lower and frequency higher. But who knows...

Because the TV inductor works OK (we need to be sure), it seems something is wrong in your TX coil, and that is a good mystery.

The best way to check is to wind another one.

Regards,

-SB

[akademiker]

V+ is 8V and V- is -6,7V.
Resistance from J1-1 to GND is around 15 Meg Ohms.
I connected an inductivity from an old tv around 7mH (3Ohms) and now it really shows 10V AC. Like it should be, right?
I disconnected everything and only connected the TX coil even without shielding with simple thick (1,5mm) wire directly to the oscillator but still only 4,8V AC. This drives me crazy.
In the Tuning &Troubleshooting thread Stefano's signal is around 8V AC, should it be in that range?

[simonbaker]

I used a 100k resistor instead of C9, the sinus at pin 1 was horrible with 47pf 68pf and 100pf. Changing back to 100pf and taking pics. Now there is no more strange signal when in middle position.

I used 0.28mm wire in the coils the TX coil has 19,6 Ohm including usb-2 cable and the RX coil has 20,1 Ohm.
V+ is 12V and V- is 0V. I use a regulated power supply, so voltage is very stable. The circuit consumes around 30mA.

Yes I am sure its 2V/Div, my multimeter shows 3.9V AC too.

R1=2,2k ,R2=24k ,R3=47k and 2n2907 is flawless. What else should i check?

Sorry, I meant the regulated V+ at the LM7808 output pin 3 (should be +8 Volts) and the negative supply rail (from Diode D6 and Capacitor C5, should be about -5 to -6.5 Volts).

Easiest place to check is the V+ and V- pins of the IC's, see the schematics. They should all (except CD4024) show +8 volts on the V+ pin and approx -5 to -6.5 volts on the V- pin.

If your V+ and V- "rails" are correct voltage, let's concentrate on your oscillator section (TR1, C1, C2, R1, R2, R3). Something seems wrong there. Make sure values of parts are correct and transistor working OK -- I guess you already did that somewhat.

It is also possible something is draining current from your oscillator, like a solder bridge between traces. Check the resistance from J1-1 (same as TR1 collector) to ground. It should be really high, mine measured over 2 Meg.

If you have any extra coil approx 6 mH, disconnect your TX/RX coils and just connect the extra coil directly to oscillator and measure voltage. If possible disconnect the cable also. This is just in case you have some wiring problem in your cable or TX/RX coils.

Regards,

-SB

[akademiker]

I used a 100k resistor instead of C9, the sinus at pin 1 was horrible with 47pf 68pf and 100pf. Changing back to 100pf and taking pics. Now there is no more strange signal when in middle position.

I used 0.28mm wire in the coils the TX coil has 19,6 Ohm including usb-2 cable and the RX coil has 20,1 Ohm.
V+ is 12V and V- is 0V. I use a regulated power supply, so voltage is very stable. The circuit consumes around 30mA.

Yes I am sure its 2V/Div, my multimeter shows 3.9V AC too.

R1=2,2k ,R2=24k ,R3=47k and 2n2907 is flawless. What else should i check?

[simonbaker]

it is a TGSL build according to http://www.geotech1.com/forums/showthread.php?t=15710

I tried to null the coils while measuring Pin 7 of LF353 and I couldnt get lower than an amplitude of 1,6V (Yes its not millivolts, but i guess its ok cuz it gets amplified, right?)

The syncs both show a nice sawblade and change their position a little. But when i turn the disc pot in the middle position the signal looks very strange and then is almost zero.

Hi akademiker:

Your null voltage at pin 7 of LF353 may be OK. Shields and cables can cause a fairly large null.

Your GB sync pulse looks normal.

Your DISC sync pulse seems to have a problem -- it is shifting 180 deg instead of 90 deg.

I think your capacitor C9 (connected at LF353 pin 2) is "shorted" or too large. Would you show schematic of any mods you made there?

Use ohm meter and make sure C9 is not shorted. Make sure it is 100 pF or less, not 100 nF, etc.

Also we need to figure out why your TX voltage is so low. What are your V+ and V- voltages? What thickness wire used for TX coil? Can you double-check resistors in oscillator? Are you sure scale is 2 V/div in your photo?

Regards,

-SB