Interchangeable mono coils?

[pray4rain]

I would appreciate if someone explained to me in layman terms whether or not I can use a coiltek mono coil made for sd/gp on my infinium. I assume it is not possible because nobody is bragging about doing it. I took apart a small nuggetfinder coil of mine that a cow ruined and was suprised at how simple it appeared. Three of the five pins on the connector were soldered to one wire, and two pins to the other. the only two wires in the cable were soldered inside of the coil to one single wire with multiple wraps. I'm sure this is not news to anyone here, but it suprised me and made me think it could possible to adapt one brand's mono coil to another brand's detector. Please explain this to me so that I can stop daydreaming about putting an 18" mono coil on my infinium.

Regards, David

 

[bbsailor]

David,

For starters, try to match the new coil inductance and resistance to your pressent coil by using the procedure below.

1. Accurately measure the resistance of the coil. Since the coil is apart, you can do this either at the coil plug or you can disconnect the coil wire from the coax and measure it from there. Plus or minus a tenth of an Ohm is probably close enough. Use either the same coax or obtain a similar coax for the new coil. See how your existing coil is shielded and do the same with your new coil.

2. Measure the diameter of the wire on the coil and find the equivalent AWG wire size. See if you can count the amount of turns with the coil being exposed.

3. Measure the inside diameter of the coil and the coil width.

4. Go to the following web site and enter what you know about the coil and see how close it comes your measured inductance in uH and the calculation result. http://my.athenet.net/~multiplx/cgi-bin/airind.main.cgi

5. Enter the new coil diameter in the above web site coil calculator and calculate the amount of turns for an 18" coil.

6. Multiply pi times the mean coil diameter times the number of turns to obtain the wire length that makes up the coil.

7. Look at the wire table and find a wire size that will give you about the same resistance for the new coil size having approximately the same inductance as the initial coil. The larger coil will have about 25% fewer turns but this is just my SWAG (scientific wild ass guess).

8. Wind your new coil and measure it. Usually it is best to wind one or two additional turns (from what is calculated), measure when wound and then remove a turn or two to get the same inductance as your present coil.

9. Find or make an 18" coil housing. Consider how you will be shielding the new coil.

10. Bring a shovel to dig up your targets.

11. Let us all know how this works out.

bbsailor

 

[pray4rain]

I believe you answered my question. I was expecting an answer explaining why I can't just throw another manufacturer's coil onto my infinium, but after reading about what building my own searchcoil would require, I can see that each searchoil needs to be "balanced" for the detector intended for use. As far as building my own goes, I didn't understand half of the terminology that you used in your instructions which is a (slight) indication that I may be out of my league. Thanks, and I hope your post can help someone who is more knowledgeable.

If you or anyone else in this forum is up for the task of building a large monocoil for my infinium let me know.

 

[bbsailor]

David,

Sorry for confusing you. Try this.

Get someone with an Ohm meter or a Volt-Ohm-Meter to measure the resistance of the coil. It will probably be between a few tenths of an Ohm to about a few ohms but this is necessary to match the wire size for a new, larger coil. Post a picture of your open (broken) coil on this forum. Let us know as much about the physical size of the coil size, wire diameter and approximate number of turns that would not be obvious from the picture. See if there is a resistor (small tubular object with metal wires coming out of both ends that may have color bands on the tubular body indicating it's value) soldered where the coil connects to the coax cable (the cable with the plug). If there is, what are it's markings? If there is not a resistor, tell us that also?

With this data we may be able to tell you what size wire and number of turns so you can make a simple mono coil about 18" in diameter. This would be no more complex than winding the specified wire size (diameter is critical), a specified number of turns (also critical but some small variation of a turn or two is OK) around a circular coil form, taping the wire bundle tight, and soldering the coax (reuse the old one) and possibly a resistor (if one is used on the old coil) to the coax connection. Anyone who has a soldering iron should be able to do this for you.

Once the coil details are known, the other forum members may be able to recommed a different coil that may work. But for the simple answer that you seek, we need some input to help. Even if another commercial coil is recommended the coil connector will need to be changed, at a minimum.

I only make coils for my own experimentation and have no wish to make them for others.

bbsailor

 

[au4greg]

Stick with Garrett. The Std DD Coil is terrific. What do you hope to gain by another coil.

Coil Geometry and tuning to the particular frequency is complex. Not just winding some wire.