Homemade KPI with an air dielectric. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies

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The variable capacitor (KPI) with an insulated rotor and stator offered to the attention of readers is structurally simple, does not require the use of scarce materials and machine work, and can be made at home by a radio amateur with elementary locksmith skills.

Of the materials you will need tin or brass 0,5 ... 0,6 mm thick (preferably tinned), a piece of sheet brass 0,8 ... 1 mm thick, pieces of copper wire with a diameter of 3 mm and a thin-walled copper tube with a diameter of 7 mm, a little sheet fiberglass 6 mm thick, a little more than a dozen M3 screws and solder (preferably POS-60, as it is rather low-melting and provides a good appearance of the solder joint), and from tools - a hacksaw and scissors for metal, files, a screwdriver or a drill, several drills and powerful (at least 100 W) electric soldering iron.

The KPE device is shown in fig. 1. It consists of a stator (parts 1, 12), a rotor (parts 5, 6, 8, 18, 19) and a housing (parts 2, 10, 11, 16, 17). Its capacity depends on the angle of rotation of the rotor relative to the stator, i.e., on the mutually overlapping area of ​​​​the rotor and stator plates, their number and the air gap between them. The stator plates 1 are fixed by soldering on the clamps 12, which, in turn, are fixed in the holes of the side bars 16 of the KPE housing. The rotor plates 5 are soldered to the shaft 6 and the latch 8. The shaft 6 rotates in the bearings 14, fixed on the slats 16 with screws 15. The axial displacement of the rotor is prevented by the restrictive washers 6 fixed on the shaft 18, abutting against the bearings 14, and in the direction perpendicular to the axis, - limiters-current collectors 7, fixed on bearings 14 and slats 16 with screws 15. The CPE case is a rectangular frame consisting of two slats 10 fastened with screws 17 and 16 and transverse slats 2 and 11.

Rice. 1. KPI design (click to enlarge): 1 - stator plate, tin, brass sheet 0,5 mm thick, 8 pcs., soldered to clamps 12; 2 - end plate, fiberglass sheet 6 mm thick, fastened to parts with 16 screws 17; 3 - nut M3, 2 pcs.; 4, 9 - M3x15 screw, 2 pcs., fix in the found position with nuts 3; 5 - rotor plate, tin, sheet brass 0,5 mm thick, 8 pcs., soldered to roller 6 and retainer 8; 6 - rotor shaft, thin-walled brass tube (section of the knee of the telescopic antenna), soldered to plates 5; 7 - current collector-limiter, steel wire with a diameter of 0,8 mm, 2 pcs., fasten to parts 14 and 16 with screws 15; 8 - retainer of rotor plates, copper wire with a diameter of 3,2 mm, 2 pcs., Solder to det. 5; 10 - screws (M3x12, 4 pcs.) fastening the bar 11 to the parts 16; 11 - strap, fiberglass 6 mm thick, fastened to parts 16 with screws 10; 12 - retainer of stator plates, copper wire with a diameter of 3,2 mm, 2 pcs., Solder to parts 1; 13 - petal, copper, brass sheet 0,5 mm thick, 2 pcs., fasten to det. 16 screw 15; 14 - bearing, brass 1 mm thick, 2 pcs., fasten to part 16 with screw 15; 15 - screw M3x6, 6 pcs.; 16 - side strip, fiberglass 6 mm thick, 2 pcs., fasten to parts 2 and 11 with screws 10 and 17; 17 - screw M3x12, 4 pcs.; 18 - restrictive washer, brass 1 mm thick, 2 pcs., Solder to item 6; 19 - pin, copper wire with a diameter of 2 mm, press into part 6 before soldering washers 18.

In the manufacture of KPI, blanks of identical parts (rotor and stator plates, bearings 14, slats 16) are recommended to be processed together by combining them into packages using rivets or screws with nuts (for this, holes with a diameter of 2,6 mm are provided in the rotor plates).

In the described version of the KPI, the stator and rotor contain eight plates each, the air gap between them is about 2 mm, the maximum capacitance is about 90 pF. Of course, the shape of the plates, their number and the gap between them may be different, here much depends on the capabilities and experience of the radio amateur, for example, it is hardly worth starting to manufacture a capacitor with a gap of less than 1 mm without sufficient experience in plumbing.

Before assembling the rotor and stator, roller 6, clamps 8, 12 and places of soldering on the plates (belts 2 ... 3 mm wide around the holes for the roller and clamps) must be tinned. In addition, it is necessary to prepare technological gaskets cut out of corrugated cardboard with a thickness equal to the air gap between the plates (i.e. 2 mm) with dimensions of 35x35 mm (their number should be about a dozen more than the number of plates). The choice of gasket material is due to the low heat capacity of corrugated cardboard, which facilitates the process of soldering the plates to the clamps. Next, to the upper (according to the figure) side bar 16, the straps 2 and 11, the bearing 14 and the current collector-limiter 7 are screwed. , formed by a semicircular cutout in the bearing 6 and current collector 19, and the ends of the clamps 18 - into the corresponding holes of the bar 14. Putting four or five cardboard pads on its inner side, put the first rotor plate on the roller 7, put the next pad on it, then on the protruding inside, the ends of the latches 12 put on the first stator plate, put the next gasket, put the next rotor plate on the roller, etc. When the number of rotor plates reaches three or four, a latch 16 is inserted into their holes with a diameter of 6 mm, and then each next the rotor plate is put on both the roller 12 and the latch 3,3.

Having put the last stator plate in place, the second bar 16 is screwed, the last few corrugated cardboard technological spacers are inserted into the gap between it and the stator plate, and if necessary, an excessive gap between them is selected with additional spacers of the required thickness. After that, the free ends of the clamps 12 are inserted into the corresponding holes of the second bar 16, and the end of the tubular roller 6 with the second washer 18 previously put on it is inserted into the cutout of the second bearing 14, the second limiter-current collector 7 is put in place and its position is fixed with the screw 15.

The mutual position of the rotor and stator plates is fixed with solder, heating the places of their soldering to the roller and clamps with a powerful soldering iron. Before soldering, the stator clamps 12 are set in a position in which their ends protrude beyond the straps 16 by approximately the same amount, and the clamp 8 - so that at maximum capacity its lower (according to the figure) end reliably abuts against the stopper screw 9.

Rice. 2. Appearance of one of the practical design options

The assembly is completed by installing the limiting screws 4 and 9 in place. The first fix the rotor in the position corresponding to the minimum capacity of the KPI, the second - in the position corresponding to its maximum capacity. The position of the screws themselves is fixed with nuts 3 (M3).

The protruding ends of the clamps 12 are carefully riveted in the holes of the slats 16. The materials of the KPE parts and some technological instructions for its assembly are contained in the caption to fig. 1. The appearance of one of the practical design options is shown in fig. 2.

Author: S. Dolganov

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