White 3900D

[dbanner]

Anyone notice that the older tesoros Rx resonates above Tx, whereas with the Whites Rx resonates below Tx.

[Nandor]

yup, we pay the depth loose for perfect discrimination. you are right.
here that i see in Kostin's text. you see primary reaction on coin and then secondary reaction, on the pics. in first case we see just phase shift without amplitude growth.

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Maybe this is a reason why the Whites designs are deeper than the Tesoro ones.
This things deserves a topic, so we could talk about the possibilities of a good compromise between discrimination and detection depth.

[MartyJ1963]

Any news yet on your build DB?,,Regards,,,Marty

[kt315]

yup, we pay the depth loose for perfect discrimination. you are right.
here that i see in Kostin's text. you see primary reaction on coin and then secondary reaction, on the pics. in first case we see just phase shift without amplitude growth.

[Nandor]

Kostin reseached that
- a reaction on unferrous at first moment is just phase shift, then after at secondary is phase shift and amplitude
- a reaction on ferrous at first and later is phase shift and amplitude, together.
from that you see why VLF two-channel classic two-comparator schematic has low sensitivity on unferrous and big sensitivity
on ferrous. because at first stage when un-ferrous channel already turns up, second all-metal channel is still in turn off state.
NO signal, no reaction.

(i do not use 'X reactive' and 'conductive R' conceptions here)

I had a bad TGSL and had to troubleshoot it. When I checked the filters I have observed that the Disc channel has more gain and it's more sensitive than the Geb channel with the same components, I even meauserd and paired them to be almost exactly the same value. I tried to raise the gain on the Geb channel by 1.5x~ aprox but no benefits of detection distance.
It is very interesting because as you say no reaction on Geb while Disc has already reacting. Because of this phenomenon classic comparator desings loose good detection depth. It would be nice to improve this drawback of these designs.

regards

[dbanner]

Kostin document is a very interesting read, I appreciate how he tried to lay an empirical basis for "off resonance" coils. The very interesting conclusions come at the end of the document, especially the temp. data.

Not sure I understand everything, but like I said before, IB coils are not necessarily balanced for minumum residual voltage on Rx, but rather close to such, and is the case with "off resonance", there appears to be an inherent phase angle which coincides with the rest of the circuitry parameters, otherwise the min/max discrim settings don't work correctly. Beyond that, things become a little fuzzy for me.

[kt315]

Kostin reseached that
- a reaction on unferrous at first moment is just phase shift, then after at secondary is phase shift and amplitude
- a reaction on ferrous at first and later is phase shift and amplitude, together.
from that you see why VLF two-channel classic two-comparator schematic has low sensitivity on unferrous and big sensitivity
on ferrous. because at first stage when un-ferrous channel already turns up, second all-metal channel is still in turn off state.
NO signal, no reaction.

(i do not use 'X reactive' and 'conductive R' conceptions here)

[waltr]

The best paper I have seen on VLF Coil resonance and has been posted here on Geotech is:
VLF coils Kostin.pdf

Very good read.

[dbanner]

She does not balance the coil.....


The coils are very close to balance simply by knowing number of turns, wire size feedback turns etc,etc, in the manufacturing process.
They make their coils to very precise quality control standards, so that in the end, the inductive balance is there merely through controlling the coil making process. The trimmers take care of the rest. That's my assumption.

[kt315]

thank you Nandor. who wanted had see the videos.

now another coil. 8inch blue max. on RX part we see 56nF cap.

[Nandor]

thats good. i did videos with 9.5 xlt coil, but youtube deleted my channel with all videos.
i sure showed HOW phase shift changing just on very small moving, 5mm...1cm..., of the balance loop. you have to see that!
very big range of the phase. i still have a coil that seems unbalanced but it is working great -!
so deal is not in phase shift, but IN RIGHT PHASE SHIFT'S AND AMPLITUDE REACTION ON A METALL, that i had told many times.

Thanks for sharing it, I've seen it on youtube. So bad that they deleted it Sinclairuser. It was a nice demonstration!

[dbanner]

Another way of looking at the residual phase offset at so called "Null", is to think of a metal target taking the balance of the Rx further away from its "null", resulting in a phase shift, the degree to which depends on the type of metal target.
If you move that tiny fine null loop around, you also see a shifting of the phase. The more "off resonance", the greater degree of shifting.????? I don't know.

The balanced coil with an initial phase offset is meant set up the calibration points from which the detector circuitry takes its gb and discrimination. But it still does not answer the question of why having "off resonance" coil.

I noticed there is matter of temperature effects on the sensitivity and stability of the loop.
Maybe I try hobby of brass rubbing. Seems much easier.

[kt315]

look on 3:09 https://www.youtube.com/watch?v=LPth6lBBGUE
she does not balance the coil. she just checks THE RIGHT REACTION ON THE METALL - moving of RX phase and encreasing of RX signal amplitude.

again - REACTION. look attentionally the video.

[dbanner]

One thing I noted, the so called "balanced" coils" in the patent states coils are balanced to the nearest zero condition. But this might not be so if one has a residual phase shift in mind, it could be slightly to the left or right of this minimum.

But what the hell do I know. All this is from reading the stuff, and my reasoning could be flawed.

Experts can say more to elucidate the topic.

[kt315]

thats good. i did videos with 9.5 xlt coil, but youtube deleted my channel with all videos.
i sure showed HOW phase shift changing just on very small moving, 5mm...1cm..., of the balance loop. you have to see that!
very big range of the phase. i still have a coil that seems unbalanced but it is working great -!
so deal is not in phase shift, but IN RIGHT PHASE SHIFT'S AND AMPLITUDE REACTION ON A METALL, that i had told many times.