White 3900D

[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

[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.

[MartyJ1963]

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

[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.

[ATTACH]48440[/ATTACH]

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.

[dbanner]

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

[waltr]

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

Yes, I have noticed but don't think it matters. It is the difference of the two resonances that produces a stable circuit with good discrimination.

The other thing I've noticed between Tereso & Whites is the inductance of the RX coil related to the TX coil.
Tereso coils seem to just have about 500uH difference whereas Whites RX coils inductance is many time higher than the TX coil.
Examples: TGS: TX = 6.0mH, RX = 6.5mH
IDX: TX = 535uH, RX = 35.6mH
Then caps are used to resonant each coil to obtain frequency difference.

[dbanner]

Yes, I have noticed but don't think it matters. It is the difference of the two resonances that produces a stable circuit with good discrimination.

The other thing I've noticed between Tereso & Whites is the inductance of the RX coil related to the TX coil.
Tereso coils seem to just have about 500uH difference whereas Whites RX coils inductance is many time higher than the TX coil.
Examples: TGS: TX = 6.0mH, RX = 6.5mH
IDX: TX = 535uH, RX = 35.6mH
Then caps are used to resonant each coil to obtain frequency difference.

Yes, I think there must be trade-offs. But a fundamental understanding of all the parameters escapes me. The choices made by whites engineers are based on data that we don't have access to, and there reasoning behind there choices are left to speculation.
There is only broad agreement on some basic coil technical data and some underlying fundamentals, but detailed analysis is sparce.

[dbanner]

The reason why I say this is because I know of no coil whose Rx resonates above the Tx resonance (tesoro), in which the Rx inductance is several orders greater than the tx inductance. I hope you understand what I'm trying to say.
So in may not make much difference on which side Rx resonates, to the math of phase angles, but it may make a whole lot of difference in other respects like coil parameters.

[waltr]

The reason why I say this is because I know of no coil whose Rx resonates above the Tx resonance (tesoro), in which the Rx inductance is several orders greater than the tx inductance. I hope you understand what I'm trying to say.
So in may not make much difference on which side Rx resonates, to the math of phase angles, but it may make a whole lot of difference in other respects like coil parameters.

I also do not know why inductance and frequency differences where chosen.


TGS: TX = 6.0mH || 20nF = 14.5kHz
RX = 6.5mH || 15nF = 16.1kHz
RX is 11% higher frequency, 1.6kHz difference

IDX: TX = 535uH || 1088nF = 6.597kHz
RX = 35.6mH || 32.8nF = 4.655kHz
RX is 29% lower frequency, 1.945kHz difference.

Also interesting that the Whites coils have such a huge inductive difference.
One possibility is the greater number to turns on the RX coil increases the RX signal (transformer ratio).

[dbanner]

Some observations:

First, the coupling between the Tx and Rx (concentric design) is stronger in the whites design where it is >50% efficiency as opposed to the Tesoro concentric, where it is significantly less. This relates to the relative diameters of the Tx and Rx coils in both designs.
Yet the tesoro Rx inductance is much less (this is counter intuitive since reducing the coupling efficiency should imply a greater turns ratio to bump up transformer action and hence the sensitivity)

Bandwidth, Q, frequency response, temp curves, ground cancelling, sensitivity, coupling efficiency, all seem to play a role in the engineering design of these coils. What a big mess indeed!

Tesoro concentric, with its weak coupling and low inductance of Rx and small difference in relative Tx and Rx inductances, seem to achieve the same depth and cancellation and some would say even better differentiation of targets. The exact opposite of the whites approach. Go figure!

[MartyJ1963]

@DB,,,Any progress on the PCB yet?,,,Just wondering whether to start my build yet,,,Thanks, Marty

[dbanner]

@DB,,,Any progress on the PCB yet?,,,Just wondering whether to start my build yet,,,Thanks, Marty

No, I have put everything on hold for the time being, another freak accident caused a serious laceration to the right hand, it's all a mess.


But I will resume construction shortly, I have everything ready to go, just waiting for the wound to heal sufficiently.
Those night outs are becoming rather dangerous.

[MartyJ1963]

Ok Db,,,,Hope the hand heals for you soon,,,,Looking forward to how your project goes and hope it's successful,,Regards,,Marty

[Artyom]

No, I have put everything on hold for the time being, another freak accident caused a serious laceration to the right hand, it's all a mess.


But I will resume construction shortly, I have everything ready to go, just waiting for the wound to heal sufficiently.
Those night outs are becoming rather dangerous.

Take care of your hands, you have only two! )

[MartyJ1963]

@Dbanner,,,Hiya DB,,,How's the hand?,,,Hope it's healing well,,,,Regards,,Marty