VLF Coil Sheilding - Tape

[woody]

I use Silver Loaded Epoxy to glue the ground wire to the tape or fabric. Seems to work very well indeed.

[Esteban]

Attach a copper wire to solder

Another suggestion for to solder "impossible" things is this:

[J_Player]

I have a question about "bumping the coil and detecting the shield":

Suppose i wind a tight layer of spiralwrap on the coil, then epoyy it, then attach the shield, then epoxy over everything with no air space. So when the coil is done, the windings cannot move in relation to the shield. They are all epoxied together as a solid circular composite of windings, spiralwrap, shield and epoxy.

Will this style of coil be susceptible to detecting the shield when it is bumped?

[Siliquae_Sid]

I'm amazed no one has thought of using carbon conductive wire to wind coils.

I spoke to a company in the US who made this stuff. The resistance is around .05 Ohms per metre.

If anyone tries it let me know what you find.

[Charles (Upstate NY)]

I have a question about "bumping the coil and detecting the shield":

Suppose i wind a tight layer of spiralwrap on the coil, then epoyy it, then attach the shield, then epoxy over everything with no air space. So when the coil is done, the windings cannot move in relation to the shield. They are all epoxied together as a solid circular composite of windings, spiralwrap, shield and epoxy.

Will this style of coil be susceptible to detecting the shield when it is bumped?

Assuming we are still talking about a balanced VLF coil then the answer is yes. The balance is quite touchy and even solid epoxy coils flex. But never mind that for a moment. You could epoxy a big old rusty nail on the coil if you wanted to and so long as it didn't move the detector would settle down and balance the nail out.

That does not mean it has no effect on the detector. If you looked at RX on the scope it would be highly distorted. Get the carbon shielding paint too close to the windings and even that can distort the signal. So its not just an issue of the coil flexing, too conductive shields will put a load on the detector that should not be there.

Charles

[Reg]

Hi Red,

I have used the copper fabric tape (different brands), silver fabric tape (schlegel) and some of the cu/ni fabric tape and the semiconductive rubber tape (3M) at less than 10 usec. Many of the coils will work down to the 7 usec range on my PI's.

It appears to be easier to get them to work at shorter delays with the fabric tape.

Again, the hard part is to get them to work at 10 usec or less if the coils are larger. That is were I have a major problem. By larger coils, I mean 11" diameter and greater. DD coils work better and allow for faster operations than mono coils.

Figure 8 coils, also called salt or anti interference coils will work at less than 10 usec also.

Now, on the Hammerhead, it would help to reduce the coil current and the gain of the preamp. Both will help in allowing for a faster delay. especially when trying to get larger coils to work at less than 10 usec.

Generally, it is a little harder to get a lead foil shielded tape to work at the shorter delays than the fabric tape. At least, that has been my experience. Eric Foster uses Lead foil at 10 usec or less, but it is my impression he finds it quite difficult to get a coil 11" in diameter to work with a 300 uh inductance.

So, to answer your question, yes, if you are trying to work at delays of less than 10 usec then it is best to find a shield that doesn't add any problems.

Reg