[HomeBrew] More variable capacitor

[N1KHB--- via HomeBrew]

Hi Ron,
   You may have a point with the metallic layer thickness, but  you may 
have missed my point about accessing the metal layer by removal of the  
protective coating and thus making contact with threaded rod and spacers in the  
form of nuts and possibly washers. This assembly process would be used  as the 
stator sections. This brings us back to the original question  of whether 
the individual rotor discs need to be electrically connected together  
remains open. If they do not, then removal of coating for those discs is not  
needed.
 
Best,
Sonny N1KHB
 
 
 
 
In a message dated 10/24/2014 6:41:02 P.M. Eastern Daylight Time,  
ka4inm at gmail.com writes:

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On  10/24/14 16:59, N1KHB--- via HomeBrew wrote:

> ** Please do NOT  cross-post messages when posting to HOMEBREW **

> Hi Dick et  all,
>     I want to build a magnetic loop antenna which  requires a  variable
> capacitor on the antenna in order to bring  it into resonance. The  
rotor-stator
> type is disliked for it's  lossy frame connection to the rotor.  Split 
stator,
> and less  popularly, butterfly capacitors are used instead. These  caps 
are
>  expensive and hard to find. Some people then come up with their own   
ideas -
> trombone capacitors with one pipe sliding inside of another,  and other
> designs are on the web.
>      Then it  dawned on me that CD's have a metal layer  embedded within, 
so
>  the idea that it might be possible to build a variable  capacitor out  of
> CD's which have that metal layer in them. The entire   mechanics are 
still only
> fragmented thoughts floating around in my  head, but the  basic idea is 
that
> I could build the stator  sections by stacking and spacing by  some
> appropriate distance  with threaded rod with the lacquer layer stripped 
away  somehow
>  for contact. Then if the rotors didn't need to be stripped too it   would
> make assembly that much easier. But if electrical contact is  actually
> necessary in the rotor plates, I would need to do that much  more work.
>     Hence the original question of whether a  collection of  isolated 
plates
> inserted into the stator area  would still function  to disallow varying
> degrees of charge  between  the "blocked" stator  plate areas depending 
on  rotor
> position. If I had a C meter, I'd be able to just  do a  mockup to see 
what
> happens. That mockup would consist of two plates  acting  as the two 
stator
> sections, with a single isolated plate  being moved into  and out of the 
stator
> plates to see if the C  value changes. So my thinking is  that if it does,
> then multiple  isolated rotor plates would act similarly on more  stator
> plates.  My intuition says that it should work, yet some say no. Mostly   
just
> trying to save some lacquer removal work in the end, but it also  became 
an
> interesting mental exercise. I should know the answer to  this with my
> background, but it hasn't surfaced as yet.
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There is not enough aluminum sputtered on to CD and  DVDs to be 
conductive, you can see right through them if the "paint job"  is removed.
There is also no way to connect a wire to the aluminum coating  on them.
If you could you really need an extremely low inductance  connection 
individual wires will not do.

You would be  better off looking into copper foil between sheets of 
glass, "compression  capacitors" have been made that way in early radio.
Whatever you build must  be effectively water proofed.

** Please do NOT cross-post  messages when posting to HOMEBREW **
-- 
Ron  KA4INM -  Youvan's corollary:
Every action results in unwanted side  effects.
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