Verator front end

[Verator]

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I do not doubt your ideas. Perhaps you have something happen. I do not argue. But what do you do in 4 quadrants? There are only 2. The second half of the circle-mirror-like reflection. What's interesting about it? In my opinion the most serious problem is not the 4 quadrants, and the suppression of soil quality. Otherwise all your noises are worthless. Depth - it's not just the range is the identification. How do you plan to suppress the ground in a jet channel? It is not easy here as it does not deduct the channel Y

[Davor]

Even with only coloured metals discrimination you are operating over 2 quadrants, as all metal channel has positive response over 2 quadrants. In case you use also the opposite phase, you are operating in 4 quadrant.

With opposite phase at the coil, every phase mirrors. So what you observe as 2 quadrants in reality have mirrored additional 2 quadrants, total 4 quadrants.

Every coil has + and - phase response, only the most common coils have + phase much stronger in the middle. I intend to use differential coils (figure 8, bicycle etc.) as well as the common coils, so 4 quadrants will come in handy. There + and - phase come equally strong. Advantages of such coils include ground cancellation at coil, better induction balance, and EMI cancellation ... quite enough reasons to do that.

The whole difference between 2 quadrant vs. 4 quadrant is in AND vs. XNOR discrimination. I can also pick any combination:
+ phase 2 quadrant AND,
- phase 2 quadrant NOR (opposite of AND),
+ and - phase 4 quadrant XNOR.

In all 3 cases target indication works the same, only at different (or all) phase responses at coil.

Say I have figure 8 coil. In positive 2 quadrant I have target identification in upper loop of the "8" while lower is mute, negative 2 quadrant I have target identification in lower, and for 4 quadrant I have both.

[Verator]

If you are going to use a differential coil that I have some experience in this regard. Make such a coil enough problem that it did deduct the ground. The response of the coil and mirror work with it is not easy. Very problematic. Search on garbage will not do. Only clean place. Large objects she sees. It subtracts them. Only minor. I made a device that works quite well with the differential coil. There, I solved the problem simply by multiplying the specular channels. All that passes the phase that is not in a phase fails. Coil works exactly the same as conventional. But the depth of detection is not high. Only for very small targets.The most important thing to set it up correctly. Otherwise there is no differential subtraction of the soil. There just is not all.Coils another type (DD, planar) should be used for its intended purpose, taking into account their shortcomings. Otherwise it will be kakafoniya. If the ground is not even depressed ... bad at all, especially with a planar coil. To search for a unique identity. There's a signal - dig. No signal - do not dig. 4 quadrants - I think it's too much.

[Davor]

Actually 4 quadrant is easy to achieve if you plan it from the start. Using comparators for discrimination makes it difficult, but when comparators are complemented with digital gates it becomes simple.

I don't expect differential coil to be perfect, only to do what it can. The rest is in a detector device to make better.

My need is to have a detector that will work good by walking speed and no swinging a coil of moderate to large size. Hence I expect differential coil and a slow motion 4 quadrant discrimination to be just right.

[Verator]

Actually 4 quadrant is easy Hence I expect differential coil and a slow motion 4 quadrant discrimination to be just right.

I have great doubts. I really have to work a differential coil and it is not easy. This is only for the salty beach. And it needs a special tool.

[Davor]

I need it for precisely the salty beaches bordering with terra rossa soil, also saturated with salt. Depth is not much of an issue because these soils are hard as concrete.

[Verator]

Perhaps there is nothing interesting. Like concrete! The sand is needed, where you can dig. When I made the first coil diff. it has not received the suppression of soil that I expected.

[Davor]

You can only count your blessings. Little more stability here, little more balanced power there ... the differential coil is only one contributor to a better device.

BTW, sandy beaches are for the likes of Barbie and Ken. We had real Greeks, Romans, pirates, tourists and other invaders here even without sand

[Verator]

My version of the generator TX. More linear than working on a bipolar transistor. Accelerates more power. Field key to better themselves showed.
Current consumption from the power supply of about 20-30mA

[Davor]

Very nice . Glad you like it . Somehow I stuck in something else and never got to making the thing myself, but I like your results very much. I have a few BS250 and may try your solution first.

Anyway, did you notice the version with 2 flip-flops to generate quadrature drive and Tx coil locked oscillation simultaneously? It could work for Verator better than the current comparator's phase shifters. You require quadrature drive for Rx, and what better quadrature than one produced by the very oscillator, and with perfect 50% duty cycle. It will be completely phase noise free.

[Verator]

Works very well BS250 better and do not. R9 is better to put the 150-200om High linearity

[Davor]

Yes, I thought of suggesting you to increase R9 as it both increases Q factor and decreases power consumption. With better Q comes linearity. Too much R9 decreases amplitude.

[Verator]

The difference between 75om - 200om amplitude of 5-7% but current consumption decreased by 10-15%

[Davor]

It is related with coil Q. R9 presents itself as a shunt resistor of double it's value (50% duty cycle) and it reduces the Q factor. Once you use a value that is near the equivalent shunt resistance of a tank, the changes are very little.

Did you plan to try the configuration with flip-flops? They are producing quadrature outputs by means of Johnson counter configuration, and produce 100% accurate quadrature regardless of oscillator frequency.

[Verator]

Apply trigger divider can be but with the condition that there will not be through the phase shift. That is, a frequency divider. It is a known issue.Adopt Dividers can. But I'm not interested because I can not influence the attitude 0 \ 90 Generally there is no problem with it.