RE: Coaxial Capacitor?

To: tesla-at-pupman-dot-com
Subject: RE: Coaxial Capacitor?
From: "Payne, Will E" <will.e.payne-at-lmco-dot-com> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Thu, 15 Oct 1998 12:45:27 -0600
Approved: terryf-at-verinet-dot-com

What a great idea !  Here's some suggestions to go with it...

Use longer lengths for ease of construction.  At 1 nS / ft, a 100 ft cable
will 'empty' in 0.1 uS.

Common 'soft' cables such as RG-8 family may work well, in fact we used them
in laser work for HV with a simple to make HV connector:  Knock the center
out of a common PL-259, extend the dielectric 6 in and terminate center
conductor with bananananana plug.  For socket, knock center out of common
SO-239 (square flange) , screw flange thru bulkhead into plastic block with
1/2 in hole 6 in deep and banananana jack in bottom.

If higher voltage and lower ESR is needed, use 'hardline' cable.  75 ohm
aluminum hardline is cheap or free in scrap lengths up to 100 ft or so from
you local CATV company, scrap dealer, or abandoned by the road.  Or hail a
Cable TV truck and ask him for some.  Homegrown connectors (low V) made with
standard N connector and a plumbing compression fitting for 1/2 in, 7/8 in,
and 1 in. sizes.  Outer conductor is solid aluminum (jacketed or bare) and
inner is copper clad aluminum.  Don't know V rating, but I bet its high.
However C/ft will be less.

Will

> > Original Poster: Bob Wroblewski <bwroblewski-at-yahoo-dot-com> 
> > 
> > Hi All,
> >   Has anyone considered using sections of RG-8/U coaxial cable as a
> > homebrew HV capacitor? The insulating dilectric is solid polyethylene.
> > The inner conductor is solid copper as is the braid shield.
> >   The capacitance is 29pf per linear foot from an Aplha Wire catalog.
> > Then 34 one foot long bundled sections equals a .001 uf cap.
> >   Start with a bundle of 15 inch segments. Strip the outer braid an
> > inch or so from one end. Connect all center conductors together,
> > likewise connect all braid sections, rolled back an inch or so from
> > the opposite end, together. Place in a 3 or 4 inch OD tube, (maybe oil
> > fill?) and cap the ends (no pun intended) and extend a stud terminal
> > to the conductors.
> >   I'm sure if this worked well someone would have tried it by now and
> > it would be spun off to others. So where's the flaw? Too costly per
> > capacitance value? Area of conductors? Thickness of dilectric?
> > Difficulty of assembly?
> >  Just thinking, I've never tried it. Comments??
>