Help Building Coil

[chlsbrns]

I need some advice!

I want to make a wide 3" or 4" x 30" or 36" rectangular mono coil to search for (mainly) gold rings in the ocean.

I'm going to purchase a pulse induction detector but don't know which would be better at detecting rings.

JW Fishers 8x puts out 100 pulses per second. Garrett's Sea Hunter puts out 750 pulses per second. Which would be better for gold rings?

When making the coil how many turns of what size wire would be best for each detector? I want to detect from shallow to as deep as possible.

Any help would be appreciated!

 

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[Alan Applegate]

I suspect there is good reason no one has answered this post.

Each and every coil is designed to work with the electronics it is attached to. Some of the requirements are: frequency, inductance, capacitance and resistance. And, coils are wound is a variety of ways. Some are circular, some are woven, some are twisted, and some defy description. Some have a single winding, and some have multiple windings. And many other variables have to be considered. Now, if you know all of these requirements, your post was superfluous. If you don't, you're out in left field.

 

[rlc1940]

Alan is correct. Winding your own coil would certainly be an exercise in futility.

 

[roaddust66]

Ask around in your home town about ham radio operators. Then you need to ask a ham radio operator who is a guy who builds his own antennas. You find this man. You tell him what freq the metal detector operates on. The HAM can calculate with a calculator how much wire you must have in your loop in order to be " resonate" on the freq the machine operates on. Its all MATH. Also a company called MFJ makes antenna analyzers. You will need to use one of these. The ham operator should have one. The heavier the gauge wire , the wider the resonate freq range. Did i lose you or are you with me. Over ?

 

[Carl-NC]

JW Fishers 8x puts out 100 pulses per second. Garrett's Sea Hunter puts out 750 pulses per second. Which would be better for gold rings?

When making the coil how many turns of what size wire would be best for each detector? I want to detect from shallow to as deep as possible.

I would easily pick the Garrett over the JWF. Winding a PI coil is actually quite easy, you'll need to figure out the # of turns to get a ballpark correct inductance, which can be done trial-n-error. Making a decent shield is the hard part. Also waterproofing. And a 3" wide coil will have poor depth, probably not a good choice for surf hunting. See Geotech for more info on building coils.

- Carl

 

[Alan Applegate]

Well, I am an amateur operator, and I wouldn't even try unless we were talking about a BFO unit. Anyone who has ever been to Garrett, or watched the "How Do They Do That" video would know how difficult it is.

I personally have built three detectors. Two were BFO units, and they do work well if the soil is not mineralized. About 1976 or so, I designed and built a TR unit. The concentric coils were the toughest part of the build. The reason they are, is that the coils need to be balanced. This requires that one of the coils have a small trimmer cap. And that cap was very hard to get just right!

It worked well on the bench, and to my surprise the discrimination worked too. Not bad for a first attempt. But putting it into a usable form proved to be the most difficult of all of the tasks. It just didn't go where I expected it to go. I ended up buying a Garrett Coin Hunter TR machine, and I never looked back!

If I gained nothing from the experience, it was an appreciation for the work the engineers go through when they develop any type of metal detector, especially a digital one! My hat is off to them!

 

[Real de Tayopa Tropical Tramp]

G'd afternoon Carl my highly respected friend. I once had a Garrett BFO wth a 24" coil, among others. somehow even though the BFO and all of it's accessories disappeared I often found myself staring at the 2' coil hanging on the wall..

Later I acquired a Sea Hunter, and when a friend asked me to help him recover his outboard in some 20 ft of very dirty water I agreed to experiment, He came up with the shielded wire and my lonesome 2 ft BFO coil was pressed into service

It's resonance was somewhat close, so we hooked it up electrically. Chispas, a partial success, a probable 25 -35 % gain over the standard 12 in coil.

So we finally retrieved his motor.

However, I personally would suggest some one like Carl who works professionally in one of the detector labs with thousands of dollars of electronic equipment and parts to do the job correctly..

Don Jose de La Mancha

 

[woof!]

"chispas" ------dang, it's been 40 years since I heard that word used that way, I think we're getting old, Don Jose!--Dave J.