looking for someone to build me a coil

[davidg]

i'm getting a goldquest PI soon and i want a custom built DD coil that is 24'' long & 5 or so inches wide.
if anyone here wants to take on the task let me know how much $$ it would run.
i'd try it myself, but i dont know jack about electronics. i'm more into mechanical things.
thanks.

[Carl-NC]

Building is coil is 97% mechanical, 3% electrical. Go for it!

[davidg]

ok. how do i get started? is there a book?

[Reg]

Hi David,

No, there isn't any book on building coils that I know of. However, if you read the info on the Hammerhead, you will get a better idea of PI's, and coils. Also, there is a book's worth of info on this forum and the PI forum. It just hasn't been placed in one convenient sequence of info.

Now, since you are planning on getting a Goldquest, then you need to tailor a coil to match what is already on the PI. In this case, I think the inductance is about 340 uh. Fortunately, anything between 300 and 350 will work but may take a little trimming to work properly. By this I mean, you may have to add an internal resistor in the coil housing or in the connector to obtain the proper damping.

Once again, I will recommend you start by using a coil housing that is available. This will limit the size to a maximum of 18 inches in length, which I think you will find is plenty long. Much longer and you will lose depth simply because of the field strength within the detection zone.

Remember, the GQ (Goldquest) is a low power unit, so it will not work as well as a high power unit with larger coils.

Now, to begin with, you will need to select a type of wire for the coil. About any size between a 30 awg and a 20 awg will work fine. I believe Eric Foster still uses the 30 awg for the GQ coils. Simple wire such as wire wrap wire can be used, as can magnet wire. Stranded wire is also an option.

What will be the difference by using different wire? Well, you will probably find that minimum delay will change due to the variation in interwinding capacitance. So, you may not be able to operate the detector at its minimum delay setting simply because of the type of wire selected.

BTW, if you go back and read some of the previous posts, you will find out a lot about different wire insulations and wire types.

Now, once you have determined the size of the coil you are going to build, then you can figure out the size of the windings. This can be done by simply laying out a string inside the form and then measuring the string. By measuring the length, you can then use this length as the circumference of a circle and determine the diameter of a round coil that can be formed to fit the desired housing. The round coil can be used to determine the number of turns of wire needed for the desired inductance. Generally, bending a round coil into the shape you want will not affect the inductance that much.

For more information, you can read some of the posts by bbsailor and others who have built coils for a CS 6 PI or other PI's which are very similar to the GQ, except for the inductance values. Reducing the inductance on the CS 6 or any PI is possible in most cases.

Now, I do not recommend you reduce the inductance of the GQ. The 300 uh to 340 uh range is low enough.

This should get you started.

Reg