Dimensions of two box detector

[Tomspol]

Hello,

I want to build my own two box detector but I'm not sure about dimensions of coils and distance between them.
I built experimental one with coils 50 x 30cm, 50cm away from each other but the whole construction wasn't very stable.
So I'm thinking about building second one with better construction.
Do you think I can use the same dimensions? And do coils need shielding?

Thanks

[homefire]

In the old two box the coils were not shielded. Emphasis OLD. Yes shield the coils to lessen EMI. The distance between Tx and Rx coil will determine how deep your detector will be sending the Field. Also detectable target size. Is your detector simple TR or VLF type ?

[Tomspol]

Thanks for reply. I'm still experimenting with the circuit but I want it to be VLF. First I want to make mechanical construction and then finish electronic. What do you think is optimal distance between coils? I was looking for dimensions of some commercial two box detectors but I didn't find anything.

[homefire]

That would depend on what your looking for I suppose. Most commercial units are like 36 inches.