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Well, I decided to try my hand at making a balanced concentric co-planer:
Outer coil: 10.5", 20 turns #30 AWG (~350 uH)
Inner coil: 5.25", 40 turns #30 AWG (~600 uH)
Bucking coil: 5.25", 4 1/2 turns #24 AWG
I used Bill Hayes 11" closed loop enclosure ("V"). I also fabricated foam forms to hold and position the coils within the enclosure (see attached pics).
Results: Extremely satified. I achieved very good balance using the foam forms to stabilize the assembly. At the bench, in a noisy environment (TV going in background about 15' away as well a washing machine and dryer running 25ft away), my HH detectecd a nickel at 23cm, and a gold wedding band at 28cm. This is about 3-4 cm better than my 11" DD.
Lessons learned: When winding the bucking coil, wind 1 less turn from calculations and leave enough lead for 1 1/2 turns on one lead and 1/2 turn on the other. This will allow fine tuning of the balance. My first inner coil I wound with the calculated bucking coil (1/4 turns in outer coil in this case) and wound up with 1/2-2/3 turn too much. I rewound coil with 1 turn less and used about a 1/3 turn after the coils were placed in the foam forms.
All in all, a very satisfting project!
Regards,
J. L. King
Outer coil: 10.5", 20 turns #30 AWG (~350 uH)
Inner coil: 5.25", 40 turns #30 AWG (~600 uH)
Bucking coil: 5.25", 4 1/2 turns #24 AWG
I used Bill Hayes 11" closed loop enclosure ("V"). I also fabricated foam forms to hold and position the coils within the enclosure (see attached pics).
Results: Extremely satified. I achieved very good balance using the foam forms to stabilize the assembly. At the bench, in a noisy environment (TV going in background about 15' away as well a washing machine and dryer running 25ft away), my HH detectecd a nickel at 23cm, and a gold wedding band at 28cm. This is about 3-4 cm better than my 11" DD.
Lessons learned: When winding the bucking coil, wind 1 less turn from calculations and leave enough lead for 1 1/2 turns on one lead and 1/2 turn on the other. This will allow fine tuning of the balance. My first inner coil I wound with the calculated bucking coil (1/4 turns in outer coil in this case) and wound up with 1/2-2/3 turn too much. I rewound coil with 1 turn less and used about a 1/3 turn after the coils were placed in the foam forms.
All in all, a very satisfting project!
Regards,
J. L. King