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Variable RF Capacitor - 0.01 pf

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Ravi Jindal

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Hello,
I am searching the range of Variable Capacitance(C=0.01pF to 1pF) .
I search on net but there is no variable capacitance available of my range.If you know anything about that to found and made of these range of variable capacitance please send me message as soon as possible.

Thanks in Advance!!!

Ravi
France
 

BradtheRad

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This is in the realm of ''gimmick" capacitors, which can be made simply by twisting two short lengths of wire together. Barely 1 pF.

You might make it variable by laying two wires alongside each other, and changing the length of overlap.

I saw one website showing how to make your own variable capacitor from wood and aluminum plates.
 

bigdogguru

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It's doubtful you will find many variable capacitors in the sub-picofarad range, as the parasitic capacitance of most mechanical devices will exceed a picofarad and the ones that do exist will be fairly expensive as many will be mil-spec.

Sprague Goodman is one possible source:

MICROWAVE SAPPHIRE PISTONCAP TRIMMER CAPACITORS

What is your specific application?
 

Ravi Jindal

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but this 'gimmick" capacitor is start 0.3 pF but i need 0.05 pF...what can i do?
 

FvM

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When you're asking for variable capacitors with 0.01 pF minimal value, did you already estimate the bare pad capacitance?
The idea sounds rather unwordly.
 

bigdogguru

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As both FvM and I have alluded to is the parasitic capacitance of a mechanical device and PCB connections would typically exceed the range of such a "gimmick" device.

You still have not indicated the specific application for such a trimmer capacitor.

Perhaps if you could elaborate on the specific application, we maybe able to offer alternatives.
 

Ravi Jindal

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Yes, i kn ow about this..
i worked on antenna phase shifter using this phase shifter i required minimum value of variable capacitor like C=0.05pF to 0.5pF or maybe 0.1pF.
As you mention above "gimmick" device it is not helpful for my project. so please suggest me any other solution.
Thanks in advanced!!
 

Ravi Jindal

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ok i got it....
so tell me there is any variable capacitor whose value will be start on C=0.08pF/C=0.1pF to C=1pF ??
 

Ravi Jindal

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0.01pF is the amount of capacitance between two short wires that are hundreds of miles apart.

I got it means.. i understand what you r saying...

so tell me there is any variable capacitor whose value will be start on C=0.08pF/C=0.1pF to C=1pF ??
 
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BradtheRad

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I have a few variable capacitors in the 10-100 pF range. Screwdriver adjust. They are little things.

I can only picture that they consist of two plates, held apart by springy action. Turn the screw and it pushes them closer together.

It should be possible to construct your own, along similar principle. I suppose copper foil is a good material for the plates. Ideally it would be solderable.
 

biff44

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**broken link removed**

instead of looking for one that starts near zero capacitance, change your circuit so it works with a capacitor .5 to 1 pf. for an series L shunt C phase shifter, just lessen the series L values until the capacitor range you can buy works. OR, add more phase shift elements to give a bigger range.
 

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