[HomeBrew] More variable capacitor

[Bill Cromwell]

Hi Sonny,

It's great to be thinking about such things. Go ahead and try your 
experiments. Let us know how it works out for you. I already did all of 
that kind of stuff in my early teens (once upon a time). It was 
cigarette and gum wrappers then. At least you will no longer have to 
take anybody's word that it isn't going to tune your mag loop antenna.

Let me offer you a hint. While you are looking up ways to deal with that 
non-conductive coating on the CDs - well that is NOT lacquer. It's some 
kind of plastic and will not react in the same manner as lacquer. If you 
don't think in the right terms you don't use the right words and your 
results will be even more disappointing.

And now..have fun with your experiments.

By the way..those mag-loop antennas have some great benefits along with 
their obvious limitations. When you have finished your McGuyver 
experiments and you want a mag loop then snatch the tuning cap out of an 
old AM broadcast AC-DC receiver (about fifty cents at garage sales 
everywhere). It will handle up to 10 watts or so on transmit across your 
loop.

73,

Bill  KU8H


On 10/24/2014 04:59 PM, 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.
>   
> Best,
> Sonny N1KHB
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