Friday, January 14, 2011

Variable capacitor idea

I have seen some designs of homebrew variable capacitor, one of my favourites is the piston type using copper tubing and coaxial cable. Why? Well it looks from the mechanical point of view the simplest to make and the most forgiving to mechanical tolerances.
Said that, here's some tests I made thinking in building one of 300pf for a long waiting antenna tuner project.


Movable part will be the coaxial cable... well correctly speaking it depends on your reference point of view...



I only have to found a smaller diameter cooper tube since this one used for tests leaves a 1mm gap to the coaxial cable and I want a tighter tolerance.
Only have to and build 10 similar pieces to get the expected capacitance.

3 comments:

Adrian said...

how long is the 30pF cable? what cable did you use?
I'm interest because i want to remove the sandard variable capacitor from my L match in my 50MHz Yagi

Ricardo - CT2GQV said...

Hello Adrian,

My test was done in a 10cm piece of rg-213 coax and about 8cm of 1.5cm diameter copper tube. keep in mind that this is just a prof of concept; it must be optimized but I am sure it will work in your aplicatiom.

73 de Ricardo - CT2GQV

Adrian-YO5PBG said...

yes, it's really recomended for my antenna, but i used for the gama match a standard variable cap.
after this winter i will implement it with coax.
thanks Ricardo for the article... it it a good remainder for me HI!