tuning circuit for coils

[asolone]

hi
which type of circuit is commonly used within the coils for tuning them?

[Davor]

As few as possible

Squeeze it and stretch it to perfection while it is not yet potted in epoxy, or whatever else you use. You may leave a small wire curl to fine tune it later on.

Whatever else you use makes your coil non-interchangeable with other detectors. Tuning is ideally a geometry thing. You can put some extra windings, trimmers... whatever, to tune your coil after the epoxy cures, however, the same effect is achievable with a small piece of ferrite that you move about the coil body and glue to the place it provides the best balance. It really works.

There is not much point placing a preamp or Tx oscillator in a coil body, unless you want to make your coils unique and non-interchangeable. There are not enough losses nor too high impedances to justify placing electronics into a coil head.

[ivconic]

Pcb looks oversized!?
Are you sure it is not a prank?

[ivconic]

On second thought; it could be x-ray shot of some very small coil and that's why pcb looks oversized. (but than those few wires that crossing the center are confusing me???)
Anyway; small pcb in coil usually holds necessary electronics, such are TX out and RX front end. At some cases only RX front end.
Why? Because of static and coupling/impedance issues that may occur in conventional designs.
Static that cables or control box electronics might receive is huge problem and sometimes is easier to prevent it with implementing RX front end in coil housing and connecting it to RX coil leads directly. Amplified and filtered signal later is more immune to "cable issues".
Minelab Sovereign and X-Terra coils are good examples for this.
So much about "active" electronics in coils.
"Passive" electronics in coils are usually there for very fine tuning. Usually consist of few resistors and few capacitors, trimmers too.
Garrett Ace coils are good example for this.

[asolone]

the coils c.scope there is a pcb with trimmer resistors and capacitors
on my project coil c.scope 1220 I had many difficulties in balancing while the epoxy catalysed, I had to add a piece of iron to bring the in-phase and minimum voltage
the circuit RX is perfectly tuned in resonance , perhaps this condition increases the difficulty of balancing?

[ApBerg]

the coils c.scope there is a pcb with trimmer resistors and capacitors
on my project coil c.scope 1220 I had many difficulties in balancing while the epoxy catalysed, I had to add a piece of iron to bring the in-phase and minimum voltage
the circuit RX is perfectly tuned in resonance , perhaps this condition increases the difficulty of balancing?

It can be that Cscope has aslo used some small styroflex cap for nulling the receive coil, this was done on the old K5000 kit ??.. connecting a cap between the hot receivecoils side to one off the both side's from the transmitt coil.. (is a Hartly osc.)
I have never made it, but you can easy test it , connect a 10-100 pf cap on the receive coil connector and connect the otherside from that cap to the transmitcoils connectors ..test both side's from the transmittcoil and see what the result is at the receive signal....

You use no screening on your small coil ?

You can also use some ferrite beats for nulling.. and small strips alu foil for phase shift...


Best regards

Ap

[asolone]

It can be that Cscope has aslo used some small styroflex cap for nulling the receive coil, this was done on the old K5000 kit ??.. connecting a cap between the hot receivecoils side to one off the both side's from the transmitt coil.. (is a Hartly osc.)
I have never made it, but you can easy test it , connect a 10-100 pf cap on the receive coil connector and connect the otherside from that cap to the transmitcoils connectors ..test both side's from the transmittcoil and see what the result is at the receive signal....

You use no screening on your small coil ?

You can also use some ferrite beats for nulling.. and small strips alu foil for phase shift...


Best regards

Ap

I do not know k 5000 kit.
is absolutely necessary to shield the coil small (nickel spray)
I built two prototypes of the other is shielded
with shielding the signal is very clean
while the resin catalyses I had to recalibrate the small coil and then add the piece of iron

[ApBerg]

I do not know k 5000 kit.
is absolutely necessary to shield the coil small (nickel spray)
I built two prototypes of the other is shielded
with shielding the signal is very clean
while the resin catalyses I had to recalibrate the small coil and then add the piece of iron

look at:

http://www.geotech1.com/forums/showt...ighlight=k5000

[asolone]

the oscillator looks very similar to that used in c.scope