Building My Own Coil!

[SwampFox]

Hi guys and Gals,

I'm new here but been hunting since 1964. I'm an Radio Frequency Electronics Engineer. I design and build all kinds of Radio Frequency devices. I have been thinking about building my own pick up loop coils. I built some years ago when I worked for a fledgling metal detector company back in the MetroTec Days. If I recall correctly it was for a BFO type detector. I am now working with VLF Motion Detection and Descriminate type detectors, and a few Pulse Induction (PI) units. Most units operate between 3.0 and 40.0 KHz. Any input would be appreciated. Thank you 😊 Laurin the old SwampFox 

[Tom_in_CA]

Regarding the possibility of making a coil, on-your-own, to compete with a manufacturer coil :  This endeavor might have been possible back in the 1960s.  When the hobby (in-so-far as individual coin hunting) was concerned, was in its infancy.  And when electronics were crude (by today's standards).   But the problem now is that the super fine-tuning exactness, to eek out the absolute depth and optimum performance, is SO exacting, that a zillionth of an inch off in your windings, can make for the difference of good vs poor depth/performance.   It's now done with computerization, and assembly line exactness (where every single coil coming off the line is exactly the same ). 

 

I know someone who tried it.  And gave up. It has gone far beyond the days of persons sitting around in their garages playing with vacuum tubes, soldering guns, radios, etc....

[Steve Herschbach]

Your best source of information and help will be the Geotech Forums

Coil Basics (PDF-506K) - This article describes a variety of induction-balanced coil methods.

Coil Parameters - Database of coil parameters Coil Winder - How to make a device that will wind coils from 3 inches to 24 inches in diameter. Construction of Coplanar Search Coils - An easy method of making coplanar-concentric search coils. About Search Coils by Dave Johnson Search Coil Field Shape by Dave Johnson

[schoolofhardNox]

I've always wondered if you could correct any sloppy windings with some tunable electronic circuit installed as well. Anyways, I always encourage others to try whatever they want to accomplish. Some of the best things invented come from tinkering around and trying unconventional or inspirational ideas. Good luck SwampFox on your endeavor. Are you located in the US by any chance. SwampFox was related to the Rev war I believe.

[bklein]

Hold out for the third edition of Carl Moreland’s Inside the Metal Detector (ITMD) book hopefully early 2024. (Discussed on Geotech) it will have new content since the earlier versions. I hope you try a Bigfoot type for the Impulse AQ or Dual Field.

[Aureous]

Ive built a few dozen coils for myself over the years, hardest ones to try are the CC and DD types, where distance and sizes between the 2 loops for tuning, sensitivity and depth purposes are the most critical parameters. Obtaining the inductance and resistance values for said loops is the 1st step. Shielding method is the 2nd. Correct parts (shell, cable, connector and wire) are very type specific too. Lots to think about when you first start out.

[geof_junk]

Steve's list above is as good as it gets.   Note the size of the coil, should be your starting point depending on your preferred target size and depth of your ground. See Searchcoil size from the lists  Steve has given above.

Searchcoil size
Most standard search coils are approximately 8 inches (20 cm) in diameter if round, or approximately 10 inches (25 cm) in length if elliptical.
Larger search coils allow covering more area with each sweep, and offer a slight increase in depth on medium and large size targets. Unfortunately they are heavier, more difficult to pinpoint with, tend to lose small targets, and provide poor target separation.
Small search coils provide superior target separation (important in trashy areas) and ability to detect smaller targets (important in gold prospecting).
Of course they don’t cover as much ground as a standard size coil. However (and this may surprise you) small search coils usually have nearly as much depth capability as standard size search coils.

[SwampFox]

On 12/22/2023 at 11:56 AM, schoolofhardNox said:

I've always wondered if you could correct any sloppy windings with some tunable electronic circuit installed as well. Anyways, I always encourage others to try whatever they want to accomplish. Some of the best things invented come from tinkering around and trying unconventional or inspirational ideas. Good luck SwampFox on your endeavor. Are you located in the US by any chance. SwampFox was related to the Rev war I believe.

I am located in the US and in Northern Georgia to be exact. The name was given me by an old gentleman who I often encountered in the Mountains of North Georgia while hiking, camping 🏕 and fishing 🎣. I've always been an outdoors person from young childhood. When I was 4 years old a friend and I spent most of our preschool days outside weather permitted. We continued that into adulthood in Scouting. I since raised 3 kids that way and they are raising their children the same. Of course Metal Detecting and Gold Panning are a part of that.

[SwampFox]

On 12/22/2023 at 3:29 PM, bklein said:

Hold out for the third edition of Carl Moreland’s Inside the Metal Detector (ITMD) book hopefully early 2024. (Discussed on Geotech) it will have new content since the earlier versions. I hope you try a Bigfoot type for the Impulse AQ or Dual Field.

The figure 8 or BigFoot is one of the designs that I want to try, since they are no longer in production. There are a lot of detectors out there that people are still using and would like accessories for besides the newest out of the box. Sure if ya got megabucks you can buy the newest, but many folks want to start detecting without spending a fortune, others like the detector that they have and would welcome some add-ons for their existing machine. 😉 so I'm looking into producing some coils. Yes I heard the guy who said I could never equal what the factory built. But as an Electronic Engineer I know for a fact there are many products that are built to the minimum standard and can always be tweaked for maximum performance by not just hitting the minimum and shooting it out the door!

[kac]

You may want to snag Inside the Metal Detector found here:

https://www.amazon.com/Inside-Metal-Detector-George-Overton-ebook/dp/B01N8WAG7L/ref=sr_1_3?crid=3B20YBN072KAW&keywords=inside+the+metal+detector&qid=1704764653&sprefix=inside+the+metal+%2Caps%2C97&sr=8-3

Should have some very helpful info and math needed for designing those coils.