Verator-M

[kt315]

schematic. I have to note again that is not mine project, I bring that I see in RU zine in hope you take attention on some new issues.

[Davor]

Apparently there are several versions of Verator and this one is quite refined. It even has a synchronised power switcher. Why are the phases extracted from Tx and not using flip flops from the common digital source is beyond me.

[ODM]

Would it be better to find the actual transmitted signal, as a resonant TX can vary with its phase properties depending on surroundings, coil deformation, etc.?

If there is a reason to use the driving signal instead of (assumedly) the radiated signal in a VLF detector, I would like to know why is this the case.

[Davor]

Amplitude stability (no AM), less phase noise (no PWM), rock solid phase for exact switching (OK, scratch that - it is not used here), brain-dead simple amplitude control, possibility to use several "channels" to avoid EMI...

Maybe Sergey_P drops in to extend the list.

[kt315]

PCB - sprint layot file. http://www.avral.ru/cd8d695bca57b471c799acebc910aa1c


(NOT MINE!)

[Sergey_P]

+ (Qtx=6...7)
+
+
...
+

[Davor]

Ah, your riddles again
OK, so I see a switch that is driven from X or Y phase shifted sources. These are extracted from Tx coil which is fine for continuous phase shift, yet not used here, and prone to transforming AM and PM fluctuations into PWM, and that one is unstopably passed through to audio. On the other hand GB and discrimination are manipulated elsewhere so the best possible way of supplying X and Y would be directly from the digital source. Two flip-flops will provide you with perfect 90° with no phase fluctuations and no PWM. And it uses less current too.
Why it was not done so already is really beyond me

[Sergey_P]

<X or Y phase shifted sources> it does not matter
!!! Uout= Ux-Ug !!! - subtracting the signal from the phase of soil

[Davor]

I'd say X and Y sources do matter if you go for stability. Most of the VLFs suck in that department, including my beloved IGSL. Anyway, please consider replacing the source with true quadrature flip-flop based one

As for DD2 in the schematic, now that I finally recognised where you are pointing to, at first I thought of it as a some kind of intelligent AGC because at that point it certainly appears as one. PWM switching is provided by 4046 and two comparators, driven by motion compensated Y channel. So in effect it is not an AGC but some very interesting 2 quadrant analog multiplier?

OK, you got me a bit confused now, but I think I have a clue where it comes from. So you have an untouched channel obtained by X switching which is in phase with the Tx, which is considered a discrimination channel in most other builds, but in this build - unlike others - it is used to extract audio. The GEB channel is extracted via Y channel and phase correction using GB potentiometer, and ground signal is extracted therewith.

Usual VLF builds rely on a deep notch at GEB channel that is adjusted so that ground vector is at zero most of the time. That's a simple vector manipulation at the switchers. So the GEB channel is generally free from ground signal if GEB setup is set right. But this build is different, and GEB correction is provided as a Disc channel manipulation via analog multiplier.

OK, you got me here. So you suggest that this active manipulation actually fixes ground balance in Uout= Ux-Ug style? That's VERY interesting.

I was considering building a Tayloe-anti-Tayloe notch thing to introduce additional holes in a phase response of a detector. I'm not that much into reducing ground as I'm into reducing sea water. It is at about 90° against the ground, and too close to small gold if you know what I mean, so I need something very sharp. Do you think this principle could work with sea surface as well? There are always some ripples on the sea surface that tend to produce annoying sound that masks somewhat metallic targets in the sands below. Do you think it is worth a try?

[Sergey_P]

<it is worth a try?>
No, VDI(target)=VDI(ground) => ! differential coil !

[Davor]

Yeah, thought that much, thanks. That rises my urge to go for a 4-quadrant Rx sooner. So far I'm not that much into VDI.

[Sergey_P]

<thought that much> Geotech little behind in the theory ( http://www.md4u.ru/viewtopic.php?f=77&t=5497 ) and practice constructing MD

[Davor]

I've seen that one and that is not new science. The only novelty is a differential coil and I thought it was obvious one. Apparently it isn't.
I'll go for a 4-quadrant Rx soon.

[kt315]

GOOGLE translated.
---
We have a signal from the synchronous detector Fig.1
Normal metal (R.Hulko) filters constant and high frequency components, Figure 2. Signals above the threshold (red line) for the presence of said target. Assessment subjected all existing number of incoming input data. To isolate the objective requires that the energy of the changing noise was less than the energy of the received signal at the target all the time interval of observation.
Phase of the received response from the ground, Figure 3 if it varies slightly in the search, but in the presence of the target (the truth, I) clearly points to a difference in the resultant phase ground target ... False (L) bursts also possible ...
Fixing the value of the received response signal from the ground (red dot, figure 1) to select the signal from ground subtracted phase differences in the moments of the received signal from the phase of the soil, Figure 4
Filtered and impose a threshold figure 5. Excess of the required energy of the signal over the noise energy is greatly reduced, which greatly increases the sensitivity of the MD, because much of the noise we subtracted a satisfying response to the signal ground phase, just subtract the low-frequency component of the signal ground.
In Verator a tentative attempt was been made to implement some elements of the metal detector ...

[Davor]

Sergey, I gave this jet another thought, and apparently, using a Disc channel to extract audio is in fact a natural method to employ a VLF in seaside! It actually has a natural zero near/at salt water response (which is tunable), and GEB correction is provided as a Disc channel manipulation via analog multiplier that introduces a zero for the ferrite-like targets. In fact it has two zeros in a transfer function, and these are exactly where they are supposed to be: at ferrites and at salt water response (also for superconductors but that does not count ).

Maybe i'd come up to conclusion as to why this rig works well much sooner if only the schematic was organised in blocks by their functions.

I think I must reconsider my understanding of a good practice in VLF metal detectors. PI detectors were sold by their ability to suppress ground, while in effect they are deaf to it. This detector can be adjusted to be deaf at precisely the soil /sea water and beat PI at its own terrain! Also PI are marketed as powerful, yet no VLF detectors tried a more powerful Tx, and when they do, boy will they rock! There is no point running VLFs with a Tx coil over 1mH anyway.

You could try my balanced Tx with your rig http://www.geotech1.com/forums/showthread.php?19730
Because it follows the ground proximity effects the same way as a Rx coil does, it should provide your rig with more accurate phase than with the crystal oscillator, and considerably more flexible for the choice of frequencies too.