[Elecraft] Toroids - Effect of Winding Spacing on InductanceandDistributed Capacitance

[David Cutter]

Your comment about spacing off the core is interesting: my Drake AMU has an 
attached balun which is constructed with the wire wound on a former which 
stands the turns off the core.  The wire is 1mm diameter bare wire and does 
not touch at any point.  I have never seen this anywhere else.  The core is 
also bare, ie no visible coating.  I do not know its material.

David
G3UNA

----- Original Message ----- 
From: "Jack Smith" <jack.smith at cliftonlaboratories.com>
To: "Ron D'Eau Claire" <rondec at easystreet.com>
Cc: <elecraft at mailman.qth.net>
Sent: Monday, February 26, 2007 6:17 PM
Subject: Re: [Elecraft] Toroids - Effect of Winding Spacing on 
InductanceandDistributed Capacitance
>
> As far as cores being non-conductive, that is true for powdered iron (the 
> typical red and yellow cores) but it is not necessarily true for ferrite 
> cores. The bulk resistivity of ferrite materials varies widely from 1E9 
> down to 50 ohm-cm, and not all (few, actually in my limited experience) 
> ferrite  cores are coated with a insulating surface. In addition, many 
> ferrite materials have an extremely high dielectric constant, which 
> suggests the need for a bit of spacing between the core and the winding to 
> reduce distributed capacitance arising from paths through the core 
> (obviously more important when the core is more