[R-390] Paper Capacitor Replacement II

[kirklandb at sympatico.ca]

Once upon a time I pulled data sheets for ceramic disk and film caps and looked at the impedance V frequency plots.
For 0.01 uf, I couldn't see a significant difference. Many manufactures indicate that the film caps are non-inductively wound.

I just tried and couldn't easy find info for ceramic caps carried by digi-key. However here is a link to a panasonic film cap
 http://industrial.panasonic.com/www-data/pdf/ABD0000/ABD0000CE23.pdf

pg 12 shows data for 0.01 uf. series resonance is between 10 and 20 MHz.

If someone can find a data sheet for a ceramic cap  with these curves one could do an easy comparison.

One thing to keep in mind: don't forget the lead inductance.

0.01uf resonates at 15 MHz with 11.3 nH.  A 1mm dia wire 2 cm long has an inducatance of 14 nH.

 (hence 1cm lead length will cause a 0.01 uf cap to resonate at 15 MHz)

> Date: Fri, 6 Jan 2012 14:37:43 -0500
> From: cptcurt at flash.net
> To: r-390 at mailman.qth.net
> Subject: Re: [R-390] Paper Capacitor Replacement II
> 
> RF bypass caps can typically be much smaller capacitance value so the 
> round disk with thick mica or other HV dielectric is sufficient and 
> easier to make at HV ratings.  They also have much less 
> inductance--important for RF Bypass application.
> 
> An audio bypass cap would be physically HUGE if it we made like a disk 
> configuration.  Likewise for coupling application.
> 
> Curt
> KU8L
> 
> 
> On 1/6/2012 2:28 PM, Barry wrote:
> > Can someone explain why ceramics are better in RF applications (such as bypass) than film-and-foil (or point me to a source that explains it)?
> >
> > Thanks,
> > Barry - N4BUQ
> >
> >
> >   On Fri 06/01/12 12:54 PM , 2002tii bmw2002tii at nerdshack.com sent:
> >> Norman wrote:
> >>
> >>> Is this what we're talking about?
> >>>
> >>> http://www.vishay.com/capacitors/list/product-42016/
> >>> http://www.vishay.com/docs/42016/42016.pdf
> >> Yes, exactly.  The 225P series are the classic Orange Drop polyester
> >> (Mylar) film-and-foil caps.  They are what most everybody means when
> >> they say "Orange Drop."  The 215P series are similar, but with a
> >> better polypropylene dielectric (they are also bigger due to the
> >> smaller dielectric constant of PP compared to PE, and more expensive):
> >>
> >> http://www.vishay.com/docs/42018/42018.pdf
> >> Note:  715P are not to be confused with the 715P HV caps rated for
> >> AC, which are hybrid metallized/foil designs.
> >>
> >> (But if you want bypass caps, I once again strongly recommend using
> >> ceramics instead.)
> >>
> >> Best regards,
> >>
> >> Don
> >
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