Nautilus revisited

[dbanner]

The balancing of such a coil with oscilloscope would be a little more complicated than a standard concentric coil. One has to manipulate 2 loops of wire for fine nulling. I'm not sure, just guessing.

[dbanner]

There is some information written there. One can clearly see 2 loops of wire.

[dbanner]

One wire is green, other is reddish, make sense to wind bifilar coil with wires of different color, so easy to know which is which.

[Skippy]

The problems of making a concentric coil with centre-tapped TX interest me. It's come up for discussion before, regarding the Teknetics T2 and the lack of concentric coils for it.
If you wind the bucking coil bifilar, you end up with one 'hot' and one 'cold' winding next to the RX coil. This may be OK, but it's possible to do better. One solution is to wind the bucking coil as two seperate windings, in opposite directions. That allows both 'cold' ends to be next to the RX coil.
There are other possibilities.

A simpler solution is to wind the TX as a conventional single-ended winding, and just run the transmit voltage at a higher level.

[kt315]

There is some information written there. One can clearly see 2 loops of wire.

blur photo. i am not able to read the note (((

[Melbeta]

There is only one way to read blurred writing. One has to print it out on a large sheet of white paper, then put the paper on a light table, put a fresh clean copy of clear or white paper on top, trace a thin line over the blurred areas, and viola, there is the writing.

The writing would concern the nulling or repairs of a particular coil and what the person did to null that coil. It is better to put the information inside the coil for easier reading, then into some computer where one would have to search for the information for a specific coil! Clever idea... The history of the coil was written inside of each coil. That was what I read from an older post from someone who watch Jerry tune a coil.
Melbeta

[Melbeta]

Well I took the challenge for Dbanner, as he has spent considerable time, on this mystery. The first notation is "#B Coil Does Not Work", then there is a date "11-5-04", and on the right side of the small PCB inside the coil, is the marker toward a PCB pad, "Receiver Output". I think this was a training coil, marked by Jerry for someone to study, keep, and use when tuning coils. The first part of the large instructions says "Head Final Balance, is done by moving wires to get maximum signal from white wire on cable Pin 4 of 5 pin connector". Then below this is another instruction, "Recalibrate is done by removing epoxy (heat) from solder ????? foam small post out of balance ????? and moving around to get maximum equal from Pin 4."

There are two wires used to balance the coil, and there is a writing showing both wires, each marked with arrows, with the words "Balance Wires".

So there you go Dbanner. Make a coil, let us know how it works, and the results. The two words marked by ????? I was not able to figure out what they were. But the gist of the writing is revealed... I do reverse engineering on vintage metal detectors myself.
Melbeta

[dbanner]

Thanks again guys, today I printed layout onto gloss paper for heat transfer to copper board. The layout is very large! It measures about 16cm x 11cm.
Problem is that the glossy paper is not so glossy! I couldn't find the high gloss paper and had to settle for the less gloss. Hope it works.

[dbanner]

The top layer is just a few tracks, so I can just use some wires to make those connections as this is only prototype.
On the issue of the coil, I found that 66 turns total for feedback( bucking coil) of 1260x was higher than the standard 1:4 ratio of "normal" concentric.

[dbanner]

I am struggling to visualize such a coil. But 1260x bucking coil is 66 turns bifilar, so from the diagram of 1260x coil, the "F(finish)" end of first 33turns would have to connect to "S(start) end of second 33 turns( with a tap which goes to ground). Thus you end up with two feedback coils in antiphase.
If that makes any sense. I think I've just run around in a circle.

[dbanner]

This means that the 1260x bucking coil does indeed maintain the approximate 1:4 ratio( 33/127) having consideration that it is center tap TX coil.
If I remember correctly, the Rx and bucking coil is about half diameter of the TX coil, in a standard concentric coplanar, the bucking coil having 1/4 the turns of TX coil.

[dbanner]

I just had a eureka moment(I think). A bifilar coil is nothing fancy, it is just the name given to method of construction. You see, in a concentric coplanar coil where there is center tap on TX coil, it is the BUCKING COIL that is center tapped! Winding the coils bifilar facilitates ease of doing this. As a matter of fact, I suspect that all concentric search heads where the TX coil is center tapped are bifilar design.

[Skippy]

... except for the problem I've just described.
Assume you wind the bucking coil bi-filar, and name the windings A and B. If you choose the end of winding A that is closest to the RX coil to be your 'centre-tap', which is 'cold', and will be at a DC potential,... then you have to choose the outermost end of winding B to be your other 'centre-tap'. Which means the end of winding B that is right next to the RX coil will be 'hot'. That is to say it has a large AC signal on it, which will couple directly to the RX coil. This could cause problems nulling the coil.
( One possible solution is to shield the RX coil from the bucking coil, I have no experience of this )

I don't see any problems occuring if the main TX winding is done bifilar.

[dbanner]

When you say "closest to Rx coil" you lost me.
I will attempt to draw sketch of how I see it's construction.
I don't see closer and further as you described( because I'm not grasping what you mean)
I see bucking coil in this case as a third part of a triaxial coplanar, where it is placed either above or below Rx coil.
Someone on another forum did make mention of triaxial coplanar, now I think I know what he was getting at.

[dbanner]

Here is concept drawing of bifilar concentric coplanar coil. I used simple 2 turn bifilar winding to illustrate how everything is connected. obviously in real coil, the correct number of turns is required. The Red, Black and shield wires refer to the 1260x loop diagram above. The beginning of flow is to the left where you see the word"Red", as you can see the bucking coil flows in reverse to tx coil, which is correct.
This drawing corresponds to the 1260 loop diagram above( the S(start) and F(finish) of the bifilar windings)