4 quadrant VLF discrimination

[golfnut]

I looked at my IDX in XY as did Don and others. You see this type of thing.

At first I thought the signals remain in top RHS for non ferrous and top LHS for Fe.

This is often where patents leave it.

But on second look the signals do extend to diagonally opposite corner/state too.

[Sergey_P]

target – point
soil – space (V)
-----
E(target) ~ S*N
E(soil) ~ V
----
1.
E(target)cx = E(target)rx
E(soil)cx = E(soil)rx
2.
E(target)cx << E(target)rx
E(soil)cx = E(soil)rx

[Davor]

more or less. The same way you rotate criteria of the discrimination in a classic Rx, you have the same here, but you just extend the processing to the opposite angle as well. Yes, in fact it is 360°but may have holes, notches, whatever.

Now, why bother? Imagine a coil just as in the picture below and the target response. Observe how the response suddenly reverses in a middle where you have ample Tx field. Now, just a step further, imagine that you can use the whole target path, positive and negative,, and that it gives a properly discriminated response. Now a final effort - see how abrupt is the signal change in the middle - that's your small target sniffer, and your pinpointer. And best of all - it is perfectly balanced, and all the wires are in the same plane.

[ivconic]

In my understanding, so called "4 quadrant" means 360 degrees.
So, if i am right: by "4 quadrant" you actually mean on processing 360 degrees of signal phase?
Do i understand this correctly?

[Davor]

I must make it going, so why not here in a fresh thread.
So far I mostly re-invented the wheal - so to speak, because most of my revelations were already invented and patented, and many of them did not fare well on the market.
I think this might be different.
As far as I know, which is not much, there are no VLF MD-s on the market that do the 4 quadrant discrimination for real. I've seen only some detectors that present the vector of the target graphically and you have to see it to know where it belongs. Please correct me if I'm mistaken.
My educated guess is that this kind of Rx will narrow the gap between VLF and PI by enabling the use of differential Rx coils. These coils eliminate EMI and most of the ground signal by their very nature, yet only one half of them is useful with a traditional 2 (or 1) quadrant Rx, and that makes them odd in comparison with the commonly used coils. One side of it works, and the other side is mute.

Now, what is the big deal with these quadrants? Here goes a little intro...

In a garden variety of a MD of nowadays you'll find 2 or more "channels" usually called GEB and Disc. These are phase aligned with ground vector, Al foil etc. thus dividing a full circle of all phases that the received signals can have in a pie-like quarters that are recognised in a phase comparator part. In a case that GEB is + AND Disc. is + you have a beeep. If either or both are "-" there is no beep. Simple as that. That's a 1 quadrant discrimination, and is usually tuned to non-iron targets.
Fine. 2 quadrant is the same, but the extra quadrant is tuned to iron.
The catch is that when a coil picks a signal from a, say, golden ring, it can come as +GEB AND +Disc, but also as -GEB AND -Disc. In order to have any indication at all for a -GEB AND -Disc situation one must build a receiver that accepts phases from the opposite quadrants. Not adjacent but opposite.

Such a receiver that gives the same indication for the opposite quadrants would work perfectly well with a differential coil, because you'd have only a narrow notch in a very middle between the Rx coils' halves, that may come handy for pinpointing.

So, how about that?