Making Bandido II - 22cm diameter DD coil

[Max]

Hi all,
I'm making a DD coil for bandido...
used 0.3 mm wire for tx coil obtaining 10KHz oscillations with 120 turns, then
used 0.12 mm wire for rx coil...(100 turns - same shape of tx)
Then overlapped in DD configuration on a piece of plywood...
Nulled RX signal at 1mV pk-pk with scope...then having bad working...on disc... lose iron disc !

Output from preamp was about 200mV pk-pk...very smooth.

In all metal seems it works but in disc thing seems really strange ...

Any idea ??? Any recipe for bandido's DD coils ???

Best regards,
Max

[Unregistered]

Relax.., you are close, I use for the Rx coil also .30mm this gives a higher Q
so it wil have more sens.( adjust caps for same resonance freq as transmit)
Wat can go wrong :
If there is some sort of echo (sens not in the midle from the coil) then you have to change the start and finish wire from the receive coil, or flip over the coil, experiment it!

The ground balance from the detector need adjusment, use some ferrit ring ore the iron stuf ( look some earlyer mail for the golden) just NOT detecting it. Keeping large silver, check it

Good luck

[Unregistered]

Make the same coil for Rx and Tx : 120 (110)windings .30 mm is ok for 22cm coil !

Good luck.

[Geo]

It is better to make a bit larger Rx coil(130 turns). Now about disc.... it is known that DD coils are not so good at discrimination (there is problem with phase shift). OK i know that someone will tell me EEEE why Minelab works OK. It is very simple "I don't Know "

[Max]

Hi guys,
thanks to all of you.
Today I'll try to make an rx coil close to the first one and test it.

Best regards,
Max