Coil Winding

[NoDad]

Hi guys,
Can any of you knowledgeable ppl tell me which type of coil construction works best.
Is it the bunched up circular cross section, the flat horizontally wound (side by side turns) or the flat vertical (side by side turns - if you know what I mean).
I've read a lot about keeping the capacitance to a minimum but this is my first attempt at building a detector.

[Reg]

Re: Coil Winding

Hi NoDad,

I have built several coils, both mono and DD designs, and have them operating down in the 10 usec range.

I prefer to just make them using a simple winding apparatus where the windings are bunched up in a circular cross section. This seems to work just fine.

I have tried to wind them flat vertical then tape and foldover but really didn't see any advantage to this setup so I have always gone back to what is the easiest and most simple.

Most likely you will find the lead capacitance more critical when you try to operate down in the very short delay region.

BTW, has anybody found an ideal cable that has low capacitance and doesn't present the problem of being detected?

Reg

[NoDad]

Re: Coil Winding

Thanks Reg,
As far as capacitance of the connecting cable is concerned, why not use an extension of the coil wire and lay each core on opposite sides of the connecting plastic tube. That should keep the capacitance down.

It means that the tube and top connector would have to be an integral part of each other and separated at the top if alternate coils were required.

When you say low capacitance cable, what are you talking about? 20pF/m? I'll have a word with a cable manufacturer I know and post something here if I find anything.

NoDad.

[Reg]

Re: Coil Winding

Hi NoDad,

Generally, a form of coax is used as the connecting cable to minimize stray noise pickup. Unfortunately, some coax's have a fairly high capacitance per foot. Other coax is easily detected when it moves.

To get down to the 10 usec range, the capacitance of the coax becomes very critical. I have made some coils using a Belden SVHS cable, but it is quite delicate and the wire size is really too small for use with a high current PI. The capacitance of the wire is around 17 pf/ft, I think.

It would be nice to find a cable with 20pf/m, but I think that will be unlikely. However, capacitances of less than 60 pf/m or something like around 17 pf/ft or less are really needed. I would like to find something in the range of 14pf/ft if possible. There are a few coax's out there in the 14pf/ft to 17pf/ft range but most have a copper coated steel core or a copper coated steel shielding. This would make them very easy to detect and as such any lead movement would be a major problem.

Reg