Coil question for Reg.

[Frank-S]

Reg, You been around a long time,have knowledge on old and new detectors.
I purshed a old garrett ADS at a flee market for $15.it workes.I know how to make
DD coils now.Do you know if the coil has electronics in it,the coil is 7" a
5.5 connector has 5 pin holes 4 around 1 in center.
Thanks Frank.

 

[Reg]

Frank,

I have never taken a Garrett coil apart but as far as I know, there are no "active" or other electronic components inside of a Garrett coil with the exception of maybe a capacitor and/or a resistor or two. By active, I mean the coil doesn't have any transistors or IC's. Typical VLF coils often have one or more capacitors or maybe resistors, depending upon how old the coil is and the detector it is used on.

Many if not most VLF coils do have capacitors and quite possibly resistors as part of the tuning or phase shift design.

Reg

 

[Frank-S]

Thanks Reg.
I will try to find a old Garrett ADS coil,opean it up and go from there.
I do better when I see how its put together.

 

[Frank-S]

Rrg, I found a old Garrett coil,opeanded it up.It had so much resan on it I could not see
any pre-amp.Restance from connector was 13.5 ohms and 3.8 ohms.I found out by useing
restance from a coil it does work.I have a 16" x 11" DD coil on my templet.restance is clise
so I tryes it on my Garrett ADS.It worked dept not to good, US nickel 10"not good for a16" coil.
This is with out a shield guess I need to learn how to fine tune a coil.
Question what is the purpose of a capacitor in a coil.
is the cap, in line with coil windings or across coil windings.
Thanks

 

[Reg]

Frank,

I have never looked inside a Garrett Coil so I am not sure just what they are doing. What few schematics or information about coils I have seen, Garrett seems to do things differently, so I wouldn't even want to speculate just what they are doing.

Now, to answer your question about capacitors in a coil, they are usually in parallel or across the transmit windings. There is a possibility a capacitor is associated with the receive windings also. Just how it might be connected depends upon the manufacturer and circuit design.

You may find it fun, but trying to build a coil for a VLF metal detector is often more effort than it is worth. To make matters worse, nothing is standardized on the design of the front end of a metal detector, meaning manufacturers have their own way of doing things and as such may not do things even close to what another manufacturer does. For example on some of the information I have seen on the Garrett, they have transformer coupled the coils to the preamp. Other manufactures may capacitive couple a coil. Still others may use a different means. Because of these differences, coils are made differently, meaning there is no set specific pattern.

Reg

 

[Frank-S]

Thanks Reg.
I will experment with the garrett coil might learn some-thing.
It might have some thing to do with fine tuneing the coil,its easy to null
a VLF coil by ear but getting more dept,not to easy.

Thanks agan.