Coil shielding....a question for Eric Foster

[Anonymous]

Hello,
it's quite a while back that there was a discussing on coil shielding. If I remember correct you mention that you use lead tape as a shield. Right? My question is, how big must be the gap in the shield? Is a half inch enough? Or how big/small should be the gap? And do you have a isolating tape (similar tape that is used for transformers) between the copper emallied wire (coil) and the lead tape? Many thanks in advance for your reply.
Regards
Chris

 

[Anonymous]

Hi Chris,
Use as small a gap as you can. The important thing is that the two ends of the shield don't touch. In my coils, the gap is where the wires come out anyway and is about 0.25in. If you can space the shield off the winding, then the coil/shield capacitance is reduced - which is good. It is important though, that there is no relative movement between coil and shield, otherwise the coil becomes microphonic, and will give false signals when you bang it on a rock.
Eric.

 

[Anonymous]

Hi Eric,
many thanks for your quick reply. I wasn't sure should I use some isolation tape between the coil and the shield or not. Now I fixed everything and it works perfect. The only thing I need to adjust new was the damping resitor value.
Regards
Chris