TESORO GOLDEN SABRE

[mikebg]

It makes sense to me that unshielded coils exhibit a more "ideal" null phase shift. The shield certainly will add some kind of coupling -- my question is, how much of that coupling is "non-magnetic" (not affected by ground ferrite) vs. magnetic.
-SB

Simon, the shield generates an eddy current signal.
Is the following your meaning of term "blob"?

[Dennis the Mennis]

I would ask you to do the "ferrite blob" test:

Put a large blob of ferrite in the overlap between your coils. Observe the phase (zero crossings) of the (now much larger) null signal. Is the phase now more similar to the null phase with unshielded coils???

-SB

What should be considered as 'a large blob of ferrite' ?
I've got two ferrite rods of 10 cm , is this enough blob ?

kind regards

DtM

[simonbaker]

Those are interesting observations by DtM and Habitbraker.


Habitbraker -- what did you mean by "good became bad too..."? Were you talking about actual air-depth detection, or observed phase of null?

There is one electronic consequence of a seriously "wrong" null phase... if you have a large null signal and a phase which makes the voltages on capacitors C12 and/or C15 go negative, you can forward-bias the JFets, which screws up the Synchronous Detector operation and can certainly mess up your detection. So watch for that condition.

It makes sense to me that unshielded coils exhibit a more "ideal" null phase shift. The shield certainly will add some kind of coupling -- my question is, how much of that coupling is "non-magnetic" (not affected by ground ferrite) vs. magnetic.

(side note to self: Something I haven't really considered is: can the ground modulate the "non-magnetic" coupling as well, perhaps through capacitive effects, and to what degree?)

(Another issue I need to think about -- how the null signal phase is affected by the "balance" of the magnetic fields between the coils. Ideally, the balance shouldn't affect the phase, just the magnitude of the pure magnetically coupled signal, since it should just affect the net flux in one direction or another. But is there more to it...?)

I would ask you to do the "ferrite blob" test:

Put a large blob of ferrite in the overlap between your coils. Observe the phase (zero crossings) of the (now much larger) null signal. Is the phase now more similar to the null phase with unshielded coils???

-SB

[habitbraker]

hello!
Yes, I also was refering to signal from output of LF353 (pin7) and TX (Collector of TR1)
I can get it working with both positive and negative phase and even that Qiaozhi said ono of them should give better results, I dont see them. Sampling places just changes polarity (GB from pos to neg going slope and disc at pos T/2 changes to neg to pos for GB and neg T/2 for Disc.) In both cases I can reject ferrite at middle of GB pot and Disc al foil at same angle of disc pot.

But some phase shift is needed because when RX is in phase if TX, there are problems.

One interesting thing I exp. :
I have made two pairs of coils. First pair(bad) was shielded with thick al foil and after doing that I, my null became 1.5Vpp min. Second pair(good) I shielded with thin kichen foil - i could achieve very small null voltage. Both worked the same.
I choosed the second pair.
Then I decided to change cable (usb I was using). After that my small null became big and phase was positive only. Good became bad too... Very big diffference just changing cable!!
How i solved it? I took RX coil from First pair(thick shield) and my RX became perfect - phase shift from +20 to -20 (about) and null as low as 200mV(at p7)
I guess that many little different coils must be made and best combination choosed (RX,TX, shield, cable).
Other thing - shield (thick or thin) makes difference, but this difference can be fixed(overcamed) with changing other variables.

[Dennis the Mennis]

Hi DtM! You'll get there because you have the right approach!

On the general topic:

Even though I've said my piece about the null phase, let's review what we mean.

1. When someone says 20 degrees, what signal is being measured? Rx coil leads, or output of LF353? Is the Rx coil connected to the PCB or disconnected (I assume connected).

2. What is the null signal phase referenced to? (The Tx signal I presume).

3. What does 20 deg mean, leading, or lagging? How do we measure lead or lag?

Diagrams would be useful to make sure we're meaning the same thing here.


-SB

1. I think when the 20 degrees phase shift are mentioned the most would refer to the output of the LF353 vs the Tx signal .

You've a good point here that all these terms can cause confusion or are not well understood.

2. I think that the most are 'suffering' a leading phase shift were the Tx is the reference and triggers the scope just like these video's I've posted recently:

http://www.geotech1.com/forums/showpost.php?p=124977&postcount=348

http://youtu.be/3hY4s6_cKw4?hd=1

http://youtu.be/zZTDKBd3Gn0?hd=1

http://youtu.be/iJKx8JJ1A8M?hd=1

http://youtu.be/N7yrp8l_fSU?hd=1

I still can't understand and just don't know why many of us can make a coil with the 'prefered' + 20 degrees and also many of us , including myself , make coils with a bigger ( >> 20 ) phase shift just like Habitbraker just posted.

Allthough we ( Habitbraker and me ) seem to get a good detection .

Perhaps it is less important as I thought ....

What I've tried to point out in the post with the video clips is that when I use unshielded coils with the correct parameters it reacts pretty much ideal (?) : correct phase shift , low residual voltage

BUT

When these same coils are shielded there is such a great difference ...

Of course there is magnetic and capacitive coupling but what is the secret overhere ?

I've used ordinary kitchenfoil not to thick wrapped around the coil and with bare wire wrapped around the shield , just like described in these threads

When I used Mylar ( at least I think it was , stripped down a VGA cable ) just like Don DFBowers did I had better 'results' .

I'm wondering right now if this due to the Mylar or the thicker isolation between the coil and shield


kind regards ,

Dennis the Mennis

[08llyj]

cables

thx a lot for this good jod eduardo1979

[eduardo1979]

Tgsl Edu conexion

[08llyj]

cable eduardo1979

Good morning
I am new and i have invested in a tgsl eduardo1979, but I don't know how to link cables k1.2.3 on the pot and which value for this one
Same things for p10.20.30 and for the sensibilitée .
Thank you for your help.

[Qiaozhi]

Thanks Qiaozhi.. It works, and best of all it's free!

Exactly! It even reads the latest docx files.
Who needs Microsoft Office Suite?

[holyuser]

When did the new TGSL EDU thread starts ?

http://www.geotech1.com/forums/showpost.php?p=127114&postcount=1

[bernte_one]

When did the new TGSL EDU thread starts ?

[dfbowers]

If you download OpenOffice, you can create PDF files from "File > Export as PDF...".
http://download.openoffice.org/

Thanks Qiaozhi.. It works, and best of all it's free!

[dfbowers]

What was the final fix on the 220 uF capacitor (parallel with 22 ohm resistor in eduardo's audio circuit) "error"? Was it to make the capacitor go to ground instead of V+ ?

Don: why is eduardo's audio circuit superior?

Regards,

-SB

The volume on Ivconic's version is not that great. However, I use headphones anyway so it doesn't really matter. I am thinking that if the 330 Ohm resistors were replaced with 100 Ohm resistors on Ivconic's version, it might be on par. Audio is such a subjective thing as it's a matter of preference. I don't know an easy way to measure duration of the audio easily but seems to be slightly longer on Eduardo's version.

[eduardo1979]

Tgsl Edu

The resistance of 22 ohms in parallel with the 220uF capacitor, it was a mistake of mine and has been corrected. I posted the correct PCB in a previous post. The audio I've used is the audio of Eldorado and I like more.

[simonbaker]

What was the final fix on the 220 uF capacitor (parallel with 22 ohm resistor in eduardo's audio circuit) "error"? Was it to make the capacitor go to ground instead of V+ ?

Don: why is eduardo's audio circuit superior?

Regards,

-SB