Self Capacitance of Coils & Shielding: Calculate & Understand

[burnit]

Hi,

I am reading conflicting things about self Capacitance when Shielding a Coil, can someone help..
IE: I have a coil of wire --say 25 turns, 250mm dia formed from looping in my hands & bound together with a non conductive thread.

I have read on some sites that there is no affect on Capacitance when the Conductive Shielding is Grounded & then on other sites they say it affects Capacitance grounded or not?

Now my questions are, how do i work out the coil to shield capacitance if i wrap a conductive shielding material around this to eliminate stray fields from interupting the received signals.

Firstly with no AIR gap between the coil & shielding material?

Then also by introducing an Air gap between the coil & the shielding material how does this effect the results?

Or is there an online Calculator to do this?

I understand i will have to leave a small gap in the ends of the shield material to avoid unwanted eddy currents circulating in it.

Thank You

 

[Phrak]

You normally don't shield with a coil of wire, but copper tape. The capacitance you seem to be referring to developes between the sheild and windings. Place dialectric (tape) between the shield and outer winding. The capacitance is inversely porportional to the thickness of the dielectric of course.

By the way, don't short the tape to itself as it wraps around (This constitutes a single turn shorted secondary.) but overlap the ends with insulation between them.