DD Coil for PI Detector design ..

[SaltyDog]

Hi All,

I would like to create a DD coil using TX/RX in a DD configuration. However, I am not sure of the phasing to achieve cancellation on the RX side.

It is my understanding that you have each could coil consisting of a TX/RX pair wound together (BIFILAR?). I presume you phase/add the two overlapping TX coils so that they are adding (max inductance), and the two RX coils as subtracting (min inductance), is this correct?

Also, am thinking of 250uH for each coil (total ~500uH TX)

Cheers

[waltr]

DD on a PI works and one of the coils I use.

Built and nulled same as for VLF except number of turns (inductance).

See my HH2 thread for details on my coil.
https://www.geotech1.com/forums/show...ake-on-the-HH2

[SaltyDog]

Thanks,
However, can't see any details on how to phase the coils, what post should I look at ...

[waltr]

Post #6 of my thread shows Scope pictures of coil nulling.
Post #14 shows response of some targets.

Phase?- Both coils are wound in the same direction, same as on a VLF DD coil.

Just look at the preamp output and if at TX Off the signal falls in the wrong direction then swap the RX coil leads.

A few other notes:
The TX coil inductance is same as if a Mono. Connect as a mono then select Damping R.
The RX coil can be a different inductance (#of turns). More turns than TX would give some Voltage Gain but also more noise pickup.
The RX coil also needs its own Damping R.

[Carl-NC]

It is my understanding that you have each could coil consisting of a TX/RX pair wound together (BIFILAR?). I presume you phase/add the two overlapping TX coils so that they are adding (max inductance), and the two RX coils as subtracting (min inductance), is this correct?

No, one coil is TX, the other is RX. Just like a VLF.

[SaltyDog]

No, one coil is TX, the other is RX. Just like a VLF.

Oh, ... I have seen what I am proposing somewhere ..
Would there be any advantages?

[Carl-NC]

You can do what you suggested but I would instead wind a single TX coil and then RX+ and RX- "D" coils. It is essentially the same concept as the Minelab DOD coil. The drawback is you get a different response sweeping left-to-right than right-to-left. If you have an accelerometer in the coil you can easily correct for this. Offhand I see no advantage in winding 2 TX+RX "D" coils with bifilar.