Total noob - making a coil, looking for details

[BillG]

I am planning on building a PI detector very soon. As part of that effort, I will need to make a coil. I realize that a coil is typically must more simple for a PI detector than a VLF. That said, I have a relatively inexpensive commercial unit (Bounty Hunter Pioneer EX) with an 8" coil. I would like to try to make a new coil for it. I have read all the articles and pages and whatnot to know what I have to do to make a coil. However, most of those references are from the perspective of making a coil to achieve a set of desired parameters. So, if I were to want to make a 10"+ coil for my BH detector (or any specific detector), what do I need to look for or test to determine the parameters. I see the 3 parameters of capacitance, inductance and resistance and I know what they are, but I have no idea how those apply specifically to coil design. I would assume, since the machine is designed for a certain resistance, I would want that to be as close as possible. How close is close enough? I also have seen it suggested and implied although not explicitly stated that lower capacitance is better. Is that true? As for inductance, I have more familiarity with digital than analog, so this is mostly a foreign concept to me. I have a vague concept of understanding of it, but from the coil design perspective, this seems to be a time/frequency component. In this case is faster or slower better?

So there are a bunch of questions. What it really comes down to, is once I get the 3 numbers for my existing coil, how close do I need to be on each number for my new coil? Oh, and one last question... Are these parameters important for the Tx coil, the Rx coil, or both?

Thanks,
Bill

[baum7154]

PI coils are generally much different than other detector types. You will probably start with a simple mono coil. If you want to search for small gold in the range of 5 grains and larger I recommend that you read my postings on 3DSS coil construction in the Chance PI Coil thread.

Best of luck!

Dan

[BillG]

I've understand that there is a difference, since the pulse is off when the receive occurs, you can use the same coil for receive that you use for transmit. When I make the eventual PI coil, I was going to do a different type. However, for a first try for things like shielding, coil forms, etc., and a general understanding plus the ability to say that I made a coil myself, I was going to make a 10"+ coplanar-concentric search coils, per the metal detector projects page on the main site. Since I would be making it for use on my Bounty Hunter, I would need to match it's specifications. I just don't know which parameter(s) need to be "as good as or better" and which one(s) need to be "as close as possible" and which one(s) needs to be "a minimum of..." It's more an understanding of 3 parameters of coil building. That way, when I build a PI coil, I can know that I need to add a loop or use a bigger gauge wire or whatever else I can do.