Actually thermoplastics are NOT majority air.... I'm not an expert here, but the dielectric constant appears to increase with thickness and probably with density of the material.
Keep in mind that the standard insulation on THHN is 0.015" thermoplastic (PVC) and that is covered by a 3-4 mill layer of clear nylon to protect the insulation on conduit pulls... I've given up trying to understand it all fully.... I've just decided to treat the entire feedline assembly from tuner (radio) to antenna as a impedance matching network.... Bottom line.... getting the impedances in band to such a level that you can tune it... ______________________ Clay Autery, KY5G MONTAC Enterprises (318) 518-1389 On 4/15/2017 8:02 PM, Wes Stewart wrote: > Why do you suppose a little bit of dielectric on the wire would make a > huge change, when the majority of dielectric is still air? > > > On 4/15/2017 3:56 PM, Clay Autery wrote: >> Thanks.... >> >> So, these numbers are for BARE copper, right? >> Using insulated wire changes things a bunch.... >> >> For instance 18 GA THHN/THWN has an approx. dc of 2.35, XLPE has a dc of >> 5 or so.... As the dielectric constant gets larger, things get real.... >> fast. >> >> 18 GA THHN/THWN... (dc = 2.35 approx.) >> >> To get the same 464 Ohms, the Center to center distance must increase to >> 7.52 inches or so... > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to caut...@montac.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
