Hi Wyndham,
No need to apologize about being "green as they come". We all start out that way.
Now, as to your request about info on building coils for one of Eric's PI's, it is something that has been discussed several times on this forum. So there is quite a bit of info that can be accessed by searching.
Now, as to the specifics, one has to be a little more exact as to which PI the coil will be for. It does make a difference in the selection of wire, the final inductance, etc. Fortunately, Eric's PI's are very forgiving so a wide range of wire sizes can be used and still obtain the desired results. However, if you want to try to duplicate Eric's coils as much as possible, I do recommend you try to use wire similar in size and try to follow his steps in building coils.
Now, it really helps to have some test equipment including a scope, an inductance (LCR) meter and a decent digital voltmeter. These tools make it much easier to tell just what is going on. A coil could be built without them but it would be much more difficult and it would be almost impossible to assure reliable operation. Many of these items can be purchased used to keep the costs down.
As for the coil winding ratio's, I prefer a 1:1 ratio between the xmit coil and the receive. In other words, my receive coil is basically the same as my xmit. At some point I may change that, but right now, I am leaving it alone. This makes the design much easier.
Now, as to the number of turns of wire needed, that is determined by the physical size of the housing and desired inductance. The housing will actually determine the size of the coil windings, which will determine the number of turns to obtain the desired inductance.
I found it is best to use one of the various programs available to help in determining the actual number of turns requires. I will then double check each coil with my LCR meter.
As for the exact overlap amount, that is something that can be experimented with. Generally, the overlap is such that there is a minimal signal in the receive with no metal present. This will occur with an overlap that is much less than you mentioned. In most cases, the width of the overlap area will be quite small. As an example, if an 11" round DD coil is to be made, the windings will have an overlap less than 1" or so to meet the criteria mentioned. This could vary some, but not a tremendous amount.
Now, I do have a wider overlap area on my DD coils for different purposes, so my DD coils are a little different, but even then, the overlap area is still much less than the overlap amount you mentioned.
Now, my main PI is a form of a GQ clone but my coils are built a little different than a standard GQ. In doing so, I decided to make the coils so they would work on three different machines including one of Eric's earlier designs the Goldscan. To do this, the inductance of my coils is less than the standard GQ and the wire size was increased. The coils still work fine on the GQ, work well on another PI, and should work on the Goldscan (GS). I just need to modify the GS so they all have the same plug.
Like I said, Eric's design allows for some differences in design. However, when making such changes, a scope is a necessity so a person can determine the ideal damping resistance.
Drop me an email if you need more info and I will try to help you.
Reg
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