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The Homemaking For Air Variable Capacitances

04/13/2017 10:14 PM

I read an electronic magazine in which there is a report on the homemaking for air variable capacitances. After reading, I became interested in air variable capacitances. So I searched some related materials and information about this topic on net, but found that it is not specific at all. Today I would like to discuss my understandings are appropriate.

The project for air variable capacitances begins now:

In some applications, a capacitor is required to provide a variable capacitance value. Variable capacitors are used in such cases. They allow for repeated changes in capacitance by mechanical and electronic means. The air variable capacitor uses air as the dielectric, consisting of two sets of metal pieces, one of which is fixed and the other is rotatable. The metal sheets are arranged in a mesh. The overlapping portions between the two sets of metal sheets can be adjusted by rotating the actuator and the capacitance is changed. But the air gap remains the same.

As the design is simple, powerful, air variable capacitors are widely used. Its most important use is for the radio frequency field, for example, by setting the resonant frequency to tune the radio. They are also important components of RF matching networks, magnetic resonance imaging (MRI) equipment and precision capacitance tables. In addition, they are also used for air and other gas performance tests.

Homemade air variable capacitors

The production of air variable capacitors is very simple. Making air variable capacitors at home requires the following steps:

Design layout for air variable capacitances

1st step, before the hardware step is to design the structural layout and the exact measurement. You can design your layout with Cadvance or any other open source software.

Mark the metal sheet

Place the aluminum sheet on the table and draw a box of 5cmx5cm. Mark the center of the first aluminum sheet and mark it as a reference for every 5cm. Place a compass at the marked hole and draw a circle with an equal diameter on each square aluminum sheet. Then, draw the vertical line with the center point of the arc as the tangent point on the arc of each circle until the end of the aluminum sheet. The number of moving pieces should be one more than the fixed film.

Cut aluminum sheet

After drawing, cut the aluminum sheet. Remove an aluminum sheet and draw a line connecting the center to the left corner. Marks the midpoint of the line between the arc and the left corner. Mark another hole at the corresponding position on the right side corner. For reference, mark all the same holes on all aluminum sheets.

Separate the moving piece from the tablet

Draw a smaller inner ring from the center of each circle and cut the upper half of the inner ring. Drill holes with a diameter of ¼ "to ensure that the aluminum sheet is free from arched, twisted and curled.

Back panel drilling

Take a moving piece and a staircase and place it on the full mesh position on the end plate. The position of the hole in the end plate is marked according to the position of the hole of the two aluminum sheets. Place one of the two end plates over the other and drill holes at the marked hole.

Assembly of aluminum

The next step is to assemble the pieces and pieces. When assembling the moving piece, remove the bolt and remove the bolt head. Place the nut on one end of the bolt and screw it to 5 cm from the end of the bolt. Then insert the first set, two washers, the second set, two washers, and so on until all the inserts are inserted. Finally, insert the stop nut. Repeat the same process and install the patch on the rear panel.

Capacitor assembly

The housing of the capacitor consists of two end plates or covers some of the insulating material. Remove the swivel panel and insert the spindle into the rear panel (to the dicing panel). Place the gasket on the shaft on both sides of the end plate. Turn the shaft to the full mesh position and fasten the other end plates. Use the retaining nut and the gasket to fix it.

Ps: Excuse me if I was wrong in words or expressions as I am a green hand in the field of air variable capacitances. I need continual learnings.

What is your idea ? Do you agree with my ideas ? Any of your ideas would be highly appreciated.

May someone would like to help ?

thanks in advance.

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Guru

Join Date: Dec 2016
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#1

Re: The homemaking for air variable capacitances

04/13/2017 11:31 PM

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#2
In reply to #1

Re: The homemaking for air variable capacitances

04/13/2017 11:39 PM

thanks for your pictures. Yes, they're air variable capacitors. Do you know how to home make it in your spare time ? thanks in advance.

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Anonymous Poster #1
#3
In reply to #2

Re: The homemaking for air variable capacitances

04/13/2017 11:58 PM

Maybe mille feuille might suggest something?

--[impersonating Crabtree]

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#6
In reply to #3

Re: The homemaking for air variable capacitances

04/14/2017 1:51 AM

First of all, thanks for your comment. May I know what the word "mille feuille "refers to ? thanks in advance.

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Anonymous Poster #1
#7
In reply to #6

Re: The homemaking for air variable capacitances

04/14/2017 1:58 AM

It's French for "a thousand leaves", a pastry with many interleaved layers, sort of like a capacitor.

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#8
In reply to #7

Re: The homemaking for air variable capacitances

04/14/2017 2:02 AM

Is it relevant to air variable capacitances ?

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Anonymous Poster #1
#9
In reply to #8

Re: The homemaking for air variable capacitances

04/14/2017 2:48 AM

Of course it is, by very definition of terms.

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Associate

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Posts: 33
#10
In reply to #9

Re: The homemaking for air variable capacitances

04/14/2017 2:57 AM

thanks again for your continual comment. You can home make an air variable capacitances on your own, then we can further discuss the following steps.

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Guru

Join Date: Dec 2016
Posts: 2914
Good Answers: 115
#4
In reply to #2

Re: The homemaking for air variable capacitances

04/14/2017 12:10 AM

One thing you didn't cover, is determining the capacitance range and the working voltage. Before you start throwing something together, shouldn't these considerations be addressed? Say you needed a 500-750 pF, 2500 V unit. What aspects of its design would differ from a 50-75 pf 250 V unit, and by how much and where?

The top pic in my previous comment is of a neutralising capacitor from radio station WEEI's (AM 590 kHz then, 850 kHz today) transmitter, Boston, c. late 1920s. Very low-capacitance, high-voltage unit.

The pedigree of the second capacitor is unknown but is an unusual concentric design featuring superb workmanship. I suspect it may have been homemade by someone having excellent machine-shop skills.

I've been fortunate in being able to find the few air-variable caps I've needed at ham-radio swap meets, and so have never had to build one myself. You can also find tons of them on eBay. All kinds.

The only capacitors I've built myself were high-voltage (30-50 kV) fixed units of around 0.01-0.05 μF. These I made from glass plate and copper foil. The largest unit weighed about 22 kg.

My advice? Build some and see how they work out. Also look at units online to see the various designs and get some ideas. This guy has a lot of close-up pix of high-quality commercial units.

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#5
In reply to #4

Re: The homemaking for air variable capacitances

04/14/2017 1:39 AM

ok, thanks for your advice. I will feel free to take your advice into consideration. thanks a lot.

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