[TowerTalk] 43' vertical mod for true resonance on 80M

[jimlux]

Rick Karlquist wrote:
> Mark Robinson wrote:
>> So maybe a polyester film capacitor? I imagine that the current is major
>> issue in the selection of the capacitor here
>>
>> Mark N1UK
> 
> The only low loss RF plastic dielectrics are teflon, polyethylene,
> and polystrene.  Capacitors made from polyester/mylar, polypropylene,
> or polycarbonate with have something like 2% dissipation factor.  IOW,
> the Q will be only about 50.  Also, they may have substantial inductance,
> being rolled up.  Not recommended.
> 

I agree with polycarbonate and polyester being high dissipation factor, 
but PP is quite low (typically <0.05%), hence the use in switching power 
supplies, etc. In that application, they couldn't tolerate a 2% 
dissipation factor.  The problem will likely be getting low enough 
capacitance in a PP cap though..