Coil Problem?

[chemelec]

Years ago, I got some "Paper Thin" PCB Material. (0.008 inch Thick.)
So I thought I would make a 6 inch diameter, Spiral Coil using this PCB.

Turned out Fairly Good, except of a couple of Tiny Breaks, which I Repaired with a Dab of Solder.
Coil inductance is 78.5uH with a DC Resistance of 5.9 Ohms.

So I Connected it to my Detector and It Won't Detect Anything??????????

Than I Thought maybe the Inductance was Too Low or the DC Resistance was Too High.

So I connected a Series String of Small Inductors Together and connected it to the Detector.
These Three Inductors I Series Measure 91uH and 7.2 Ohms.
Connected to my Detector, Each of these 3 Coils, Detects Metal.

Even 3 of a lower inductance and Higher Resistance, also Detects Metal.

SO, Why won't the PCB Coil Detect Anything?

ANY SUGGESTIONS?

[ODM]

I'd imagine the field shape for that flat coil will be highly focused in the center of it, while the wound inductors probably have a ferrite core that extends their field notably outside of the solenoid winding.

Flat coil field:


Cored solenoid field:


Traditional loop field:

[chemelec]

Previously I wound this 4 inch coil and it works OK.
(Teflon coated wire.)

But too difficult to wind the start point with a Smaller diameter.

That Previous Coil Detects NOTHING, Not even a Large PLATE of Steel.

[chemelec]

What Else is Strange, If I Measure the Signal at the Output of the first TL081, It SHOWS DEFINITE DETECTED SIGNAL.
No Different than using my Normal Coil.

But seems the signal stops there.

[green]

What Else is Strange, If I Measure the Signal at the Output of the first TL081, It SHOWS DEFINITE DETECTED SIGNAL.
No Different than using my Normal Coil.

But seems the signal stops there.

If a metal target causes the scope signal to change at the output of the first amplifier. What does the scope signal of the next stage look like?

[chemelec]

Problem Solved, I was trying this coil on my Original Proto-type unit on my workbench.
Think this one must have a Bad Solder Connection Somewhere.

Because I Connected it to my Normal PI Detector and No Problem.
Coil Works pretty good.

Thank Guys, for all the Comments.