WHITES DUAL FIELD COIL

[Jose]

ive now sorted out my dual coil and very happy with the results im getting from this coil

Daverave.
Glad the proper functioning of your coil.
The values I posted were the ones who were in my MD, but all my coils and detectors are made in house, so may be far from reality.
However, the general rule for the damping resistor, is the largest value that does not produce oscillations.
Again, I'm glad that you get good results, I invite you to publish the final scheme, so we can all appreciate.
A Cordial Greetings
Jose

[daverave]

what a very bad time ive had putting resin in my coil !!! i rushed the job and didnt make sure the coil was perfectly level so resin was uneven and poured out onto the carpet and over my work bench and also the small inner coil must have come unstuck and lifted so i could not get perfect covering of the coil with resin...it was a total nightmare cause of my inpatience....my room carpet ruined in our rented flat.

[daverave]

are the whites tdi and surfmaster dual field coils the same...or is tdi coil different configuration ????

[Carl-NC]

Same configuration, just slightly different inductances.

[daverave]

i guess the tdi will have lower inductance as it detects small nuggets...is it true tdi can reject iron ????

[Carl-NC]

Actually, the TDI runs 300uH and the SMPI is 240-250uH as I recall. The TDI has a very limited ability to reject iron, mostly in mild ground.

[Waikiki_Sweep]

There is no reason to put resin into PI coils. Only balanced coils like VLF are required hard and strong construction to keep that precise balance.
PI coil you can bend, shake, deform and it will be working anyway. So you can use small amount of light weight materials to build the coil and make it as light as you can.
Light coil is a gift!!! You will see it in the field after sweeping a two pounds "brick" of epoxy for several hours every day and finally ends up with arthritis.

[Waikiki_Sweep]

Also I have to tell that Dual field coil is relatively light weight.
Looks like it filled with foam so you can see it floating in water.
You have to apply some force to push it down to the ocean bottom.
(Heavier neutral buoyancy coils accessible too)

[daverave]

i have now completed 2 surf pi detectors....one with normal mono coil and the other with dual field coil....and i must say the mono coil go's deeper than the dual field coil on gold items so im still not convinced by dual field...and i feel that i will stick to mono coils in the future.