Coil testing completed

[James]

I have concluded my testing of various coils, I thought I might post my results for anyone who might be interested. I tested with three different detector, The PI-1 in the Meatal Detector Handbook, Surf PI-1, and the Hammerhead board. The diameters of the coil forms were as follows, 20 CM, 25 CM, and 30 CM. I used #30 PTFE, 100/46 Litz wire, 400/46 Litz wire, 22 gauge enameled, and finally 28 gauge speaker wire. I found the coils to work about the same depth for a given diameter. I tired solenoid winding and basket weave. The coil detection results ran from the radius to almost the diameter of any given form. I did this test in are using the same metallic materials. I found the best of all the test subjects was the basket weave, 25 CM with 400/46 litz wire. My hope as this information might help members of the board in the future. Best to all Jim

[Tim]

Do you have some inductance measurements please Jim?

[James]

Tim the inductance was between 310 uh and 375 uh for all the coils. The resistance was between 1 and 2.2 ohms. I am sorry I did not write down each coils spec's, I got lazy an figured that if was in the ball park I would tested the coil. By the way you wouldn't happen to know the size of Litz wire the Minelab company used to make their coils ? Best to all Jim

[waltr]

I would expect depth as you describe for same target.

How did they do on Small, High conductive targets- a 0.5 Gram Australian gold nugget?
This is where the basket weave and/or Litz should show a difference if they are build with lower C and have a proper value Damping R.

Like to see your results.

[James]

Waltr, I thought the basket weave with the Litz wire would produce a higher "Q" coil. The basket weave did have a much lower 'C" . I did tune the damping resistor to fit each coil. I tested with very small gold fillings I retrieved from a friend who is a dentist. My test were run with various U.S. coins an other metal objects. I think My best find is a Japanese (Sin ) coin. The size is about the same diameter as a US quarter, base material is copper. Best to all Jim

[Tim]

By the way you wouldn't happen to know the size of Litz wire the Minelab company used to make their coils ?

400/46 sounds right. I remember reading it somewhere ages ago-probably here.(Try advanced search "litz" in coils).
Enamelled basket weave is my choice, as litz of any kind seems darn hard to find and is costly.
I have a 10x5 ML commanderDD & Coiltek 11DD that I use for my comparisons.

[waltr]

Waltr, I thought the basket weave with the Litz wire would produce a higher "Q" coil. The basket weave did have a much lower 'C" . I did tune the damping resistor to fit each coil. I tested with very small gold fillings I retrieved from a friend who is a dentist. My test were run with various U.S. coins an other metal objects. I think My best find is a Japanese (Sin ) coin. The size is about the same diameter as a US quarter, base material is copper. Best to all Jim

Basket weave is to reduce inter-wind C.
Litz to to reduce Eddy currents in the Coil.

A Gold filling may NOT be Pure Gold (24K). The conductivity of Gold DROPS a lot when alloyed.
Example of a Gold 14K ring (58.3% Au, 33% Cu, 5.5% Ag) is more like a US Nickel with a conductivity of about 2.6MS/m. Whereas 24K (>99.99%) is 24MS/m and a Krugerrand (22K-91.67%) is 10MS/m (lower than brass).
Gold nuggets can be fairly pure (the ones found in Australia are 95-98% so have higher conductivity and very fast Decays.

[James]

Thanks Waltr for the nice reply, I got curious about another Litz wire coil. I ordered 660/46 wire, basket weave form , and 20 CM in diameter. We will see how it performs. Thanks again Best to all Jim