Nautilus revisited

[Melbeta]

I grasped the movement of your coils, but I have a question. I always thought when the Tx coil was wound clockwise direction, the Rx coil had to be wound counter-clockwise direction??? I think that was what Skippy was saying??? Perhaps either Carl or George should jump in here right now before you wind the coil.

Now I heard that Compass when they made their DD coils for the Compass Yukon machines, moved the two wires of the bucking coil around, to get it into perfect null.
Melbeta

[Qiaozhi]

I grasped the movement of your coils, but I have a question. I always thought when the Tx coil was wound clockwise direction, the Rx coil had to be wound counter-clockwise direction??? I think that was what Skippy was saying??? Perhaps either Carl or George should jump in here right now before you wind the coil.

Now I heard that Compass when they made their DD coils for the Compass Yukon machines, moved the two wires of the bucking coil around, to get it into perfect null.
Melbeta

Looking at the schematic in post #129, it is clear that the TX is a Hartley oscillator which requires a centre-tapped coil, unlike the Colpitts which requires a single coil.
As I discovered with the off-resonance probe in ITMD (that also uses a Hartley oscillator) the two windings need to be in anti-phase, otherwise the oscillator will fail to start up. The reason for using bifilar windings (i.e. a twisted pair) is to end up with two windings that have similar characteristics. If you were to simply start winding with a single wire, stop at the centre-tap point, and then continue with the second half of the coil, the result will be two windings with different characteristics.

It would probably make your life much easier if you replaced the Hartley oscillator with a Colpitts, and hence remove the unnecessary complication of having two bucking coils. If your intention is to replicate the original design as closely as possible, then you'll just have to experiment with the coil to get the best results. It seems to me that the coil construction is the tricky part of this design. At the moment I'm not sure there is any advantage to be found by using this method of coil construction in a VLF design.

[kt315]

to information

poliaki copied fisher 555 (or 553 -?) and recall it ALL-1. ALL-1 uses this tipo of coil. open folder in Fisher_Gemini -> 555> All-1 and look
files. i mean archive DVD.

[kt315]

poland polish ALL-1 detector and their coil

...... .....

[Qiaozhi]

to information

poliaki copied fisher 555 (or 553 -?) and recall it ALL-1. ALL-1 uses this tipo of coil. open folder in Fisher_Gemini -> 555> All-1 and look
files. i mean archive DVD.

The poliaki circuit uses a centre-tapped coil, but it's not a Hartley oscillator. The TX oscillator is an astable multivibrator. The intention is most likely to provide a more powerful signal.

[Skippy]

Here's what I'm trying to describe:
(see attached pic)
With a single-ended bucking coil, wound outside the RX coil, you see that the outer-most windings of the RX are grounded, and the inner-most bucking coil windings are grounded ( or some fixed DC voltage). This results in minimal capacitive coupling between the two - only magnetic coupling.

If you wound the bucking coil bifilar, you wouldn't be able to achieve this. There would be a 'hot' winding next to the RX.

But if you wound the bucking coil as TWO SEPERATE coils, side-by-side, with one wound the opposite direction to the other, it is possible to join them up so they are centre-tapped, with BOTH cold ends of the bucking coils being next to the RX outer cold windings.

This is probably not too hard to make in mass-production, with machine-wound coils and self-bonding wire, but a bit of bother for home-built gear.

( What Melbeta said about the bucking coil being wired up opposite to the main TX is correct ..... but it wasn't what I was referring to. Hopefully the diagram explains it..)

[Melbeta]

So the TWO Cold wires, on the double winding coil, are jumped together between the two cold side wires? Or is it not clear in that spot? Looks like they might be jumped together in that area where the two windings are close to each other.

I cannot quite grasp what is going on in the IIB with block illustrations. Can you draw it out better? Direction of the windings?
Melbeta

[Skippy]

I'm not trying to describe the 2b coil, I've no idea how he's made them, I've never seen one, I can't make out much from the blurry photo posted earlier.
I'm trying to explain how I think a suitable coil COULD be made.

In the second diagram, the two 'C' wires would be joined to form the centre-tap.

And in the last diagram, you would also join the two 'C' wires together, to form the centre-tap. So a 'theoretical DC current' would flow from:
'H_a' to 'C_a' to 'C_b' to 'H_b'

[dbanner]

I have observed that the two bucking coils on either side of the center tap must be confluent in order to be in anti-phase( necessary for Hartley oscillator to work). That goes for the main TX coils as well.
In your configuration, they must be kept in anti-phase(otherwise Hartley oscillator won't oscillate), but they will cancel each other out.

I do not propose to wind bucking coil over Rx coil.
I would cut three grooves of equal diameter right around the circumference of a 3/4 inch thick spool of appropriate diameter, the center groove for Rx windings.
The two outer grooves for each bucking coil, so rx is like sandwich between the two feedback(bucking coils).
The Rx coil is considerably more windings, so groove will have to be nice width and depth to accommodate such.
All three windings separated by mere millimeters of spacing.
This could be famous triaxial coplanar.

[dbanner]

Or if I decide to stick to bifilar feedback, just two grooves would suffice, one for Rx, other for bucking.

[dbanner]

If you wind feedback coil over Rx coil, this is not so good because by the time you are finished windings of Rx coil, your inner diameter of the bucking coil is now at the outer diameter of Rx. Unless you compensated for this, your calculations will be thrown off and you coil will be hard to balance,( you're going to have to subtract turns by guess to bucking coils.
This is why to make things easier, inner diameter of both Rx and bucking coils should be made the same to make calculations precise, so your coil will balance.
Hence my reason for winding them adjacent to each other rather than on top of each other.

[dbanner]

To make things even more interesting, I think the Rx coil for the 2b is tuned "off resonance" . This has nothing to do with balancing the coils, but without knowing what frequency, well using inductance posted by other member and 22nf cap seen on coil photos, the Rx coil looks to be tuned somewhere around 11.8khz.

[Melbeta]

Remember this clue. Jerry worked closely with a fellow down in Florida, who made metal detectors to work on white sand. There was no black sand there. In the Nautilus 2B modes 3 and 4 were designed to work in WET BEACH SAND, which John Earle discovered one needed greater degree adjustment ability to tune in targets in wet sand. The salt water changed the tuning pretty much. The Nautilus was not only used for finding CIVIL WAR targets, it was used by searchers of the beaches down and around the Gulf of Mexico.

So what you find inside the coil is pretty significant to know. The Manual does say 14 KHz frequency.
Melbeta

[dbanner]

Melbeta, you definitely know your stuff. While the tx coil transmits at 14khz, the Rx coil is tuned off resonance to a freq. of 11.6khz or something around there.(not sure exactly what frequency) This tuning is critical to the proper functioning of ground balance and discrim parameters of the circuit. I still haven't worked out why Tyndall never implemented a wide scan search coil. Maybe it couldn't work with search loop balance null pots.
My attempt to make pcb turned out to be disastrous. The low gloss paper didn't transfer the toner very well. Need to start over with high quality glossy paper.
In my country when you ask for something by proper names and specs, you might as well be speaking a foreign language. So I have to say "the very shiny stuff"

[Melbeta]

Okay, when I used to make my own PCBs, I woiuld use a plain paper copier which used black toner. Now later when the computers came out, I would use a computer printer, which pirnted with black LASER toner, which worked better then the copier toner machines. But other guys used clear plastic sheets, like the sheets used to cover paper copys.

Just use your wife's clothes iron, set it for cotton ironing, And clean the copper PCB and then iron it on. Touch it up with Sharpies PERMANENT black marker pens, and it works.

After you use the developer acid, plate it with nickel solution if you have it.

Now if you are going to make double sided PCB, before you develop it, drill the holes. Then you can line up the other side pattern to the holes, and then iron that second side on.

It worked for me.

Yep, I think you found how Jerry was making his coils work deeper and better then other machines for both white sand and in the Civil War battlefields!
Melbeta