Encyclopedia of radio electronics and electrical engineering / radio reception
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To fine-tune the radio receiver to the frequency of the received radio station, a vernier is needed - a mechanism that converts the rotation of the tuning knob into a rotation of the tuning element (for example, the KPI rotor) at a relatively small angle. To successfully perform its functions, the vernier must have a sufficient gear ratio and practically no backlash.
The proposed friction mechanism has a gear ratio of about six and is designed to work with a self-made KPI with an air dielectric, described by the author in "Radio", 2016, No. 12, p. 28, 29 (it is only necessary to place a 6 mm thick gasket between the KPE body and the receiver chassis). Of the materials for its manufacture, you will need sheet fiberglass with a thickness of 1; 1,2; 1,5, 2 and 6 mm (instead of fiberglass 6 mm thick, organic glass or polystyrene of the same thickness can be used), fiberboard 6 mm thick, a strip of transparent organic glass 1,5 ... 3 mm thick, a piece of thin-walled brass tube with an outer diameter 7 mm (the author used the elbow of a telescopic antenna), epoxy glue and standard fasteners (M3 screws and nuts, several self-tapping screws and screws), and from the tools - a hacksaw, files, an electric drill, a set of drills and a set of taps for threading M3 .
The vernier device is shown in fig. 1. The drive disk, consisting of two fiberglass disks 27 glued together, the same number of washers 28 and gasket 29, is glued to the roller 3, on the left (according to the figure) end of which the tuning knob 2 is fixed. The roller rotates in bearings 4 and 18, screwed to plates 5 and 20, which, in turn, are fixed to the chassis of the receiver 26. The movement of the roller in the axial direction is prevented by washers 22 put on it and pins 21 pressed during assembly.
Rice. 1. Friction vernier device: 1 - the front wall of the receiver housing, fiberboard, fasten to the bar 11 with 3x20 screws, and to the chassis 26 - with screws 23 with nuts 25; 2 - tuning knob; 3 - roller of the drive disk, brass tube (knee of the telescopic antenna); 4 - bearing 1, fiberglass 1,5 mm thick, fasten to det. 5 screws 19; 5 - large plate, fiberboard, fasten to chassis 26 using corners 24 and screws 23 with nuts 25, and to bar 11 - screws 3x20; 6 - screw M3x15, 4 pcs.; 7 - arrow holder 10, fiberglass (organic glass, polystyrene) 6 mm thick; 8 - roller of the driven disk, brass tube with an outer diameter of 7 mm (knee of the telescopic antenna); 9 - screw M3x6, 8 pcs.; 10 - arrow, organic glass 1,5 ... 2 mm thick, fasten to det. 7 screws 9; 11 - bar 20x20 mm, wood; 12 - driven disk, fiberglass 1 ... 5 mm thick, fastened to the holder 13 with screws 9; 13 - holder of the driven disk, fiberglass (organic glass, polystyrene) 6 mm thick; 14 - clutch clamps for transferring rotation from the vernier to the KPE rotor, fiberglass (organic glass, polystyrene) 6 mm thick; 15 - KPE rotor shaft; 16, 17 - coupling parts, brass, bronze 0,5 mm thick, fasten to parts 14 with screws 9; 18 - bearing 2 (it differs from bearing 1 in the diameter of the holes for the mounting screws, indicated in brackets on the drawing), fiberglass 1 ... 5 mm thick, fasten to det. 20 screws 19; 19 - self-tapping screw M3x8, 8 pcs.; 20 - small plate (its contour and holes for screws fastening to the corners are shown in the drawing of the plate 5 with dashed lines), fiberboard, fastened to the chassis 26 using corners 24 and screws 23 with nuts 25; 21 - steel pin, 2 pcs., press into det. 3 at the final assembly of the vernier; 22 - steel washer with an inner diameter of 7 mm, 2 pcs., put on det. 3 before pressing pin 21; 23 - screw M3x12, 8 pcs.; 24 - furniture corner, 4 pcs., fasten to plates 5, 20 and chassis 26 with screws 23 with nuts 25; 25 - nut M3, 10 pcs.; 26 - receiver chassis, fasten to the wall 1 with screws 23 with nuts 25; 27 - cheek of the drive disk, fiberglass 1,5 mm thick, 2 pcs., Glue to det. 3 and 28 with epoxy glue; 28 - washer, fiberglass 2 mm thick, 2 pcs., Glue to det. 3 and 27 with epoxy glue; 29 - gasket, fiberglass 1,2 mm thick, glue to det. 3 and 27 with epoxy glue (click to enlarge)
When the tuning knob 2 is rotated, the torque is transmitted from the drive disk to the driven disk 12 due to friction, which is fixed with the help of a holder 13 and screws 9 on the roller 8. The disk 12 is made of fiberglass 1,5 mm thick. The large cutout area for the drive disk makes it flexible, which compensates for possible misalignment of rollers 3 and 8 and the non-flatness of disks 27 and 12. of the radio receiver body 8), on the other - a coupling connecting it to the shaft 7 of the KPE rotor, consisting of two holders 9 and flat springs 10 and 1 fixed to them with screws 15. This mechanism assembly is designed to compensate for misalignment of the shaft 14 and the KPE rotor.
In the manufacture of vernier parts, special attention should be paid to drilling holes with a diameter of 7 mm in parts 4, 7, 12-14 and 18. Firstly, it is recommended to first drill them with a drill with a diameter of 2 ... 3 mm smaller than required, and only then drill to the desired diameter with a well-sharpened drill bit. And secondly, try to ensure that the axes of these holes are perpendicular to the plane of the named parts. It is best to use a ready-made or make your own special drill holder, which ensures that the axis of the drill is perpendicular to the plane of the workpiece. All holes in paired parts (bearings 4 and 18, plates 5 and 20) are recommended to be drilled together, connecting them during processing into one common package. A cut about 3 mm wide in parts 7, 13 and 14 is made with a hacksaw.
The assembly of the mechanism begins with the drive disk assembly. Its details 27-29 are glued to one another and to roller 3 with epoxy glue. Since the friction between disks 12 and 27 necessary for the operation of the vernier arises due to the deformation of the latter, the thickness of the washer 29 should be selected so that after gluing the gap between the disks 27 is 0,2 ... 0,3 mm less than the actual thickness of the disk 12 .
Next, bearings 5, 20 and corners 4 are screwed to plates 18 and 24, and holder 12 to disk 13 (for fixing the first, self-tapping screws 19 are used, the second - screws 23 with nuts 25, the third - screws 9). After that, the roller 3 with the drive disk is passed through a semicircular cutout in the driven disk, then through the lower (as shown in the figure) holes of the bearings 4 and 18 and the drive disk assembly is installed on the chassis 26 so that the plates 5 and 20 are at a distance of about 25 mm one from the other. Slightly releasing the screws securing the bearing 18 and changing its position relative to the plate 20 within a small range (the diameter of the holes for the screws 19 quite allow this), they achieve an easy rotation of the roller 3 with minimal friction, after which metal washers 22 are put on its ends protruding beyond the bearings. and fix its position in the axial direction with pins 21. Axial play, if necessary, is chosen by selecting the thickness of the washers.
Further, the edge of the cutout of the disk 27 is inserted into the gap between the disks 12 from below and through the free (upper in the figure) holes of the bearings and the hole of the holder 13, the roller 8 is threaded. Clamping it in the holder 13 with a screw 6, fix the handle 3 on the end of the roller 2 and check the mechanism in operation - during its normal operation, it is almost impossible to hold the roller with 8 fingers while turning the knob 2.
The assembly is completed by installing holder 8 on roller 7 with arrow 9 pre-fixed on it with screws 10 and holder 14 with spring 17. The second part of the coupling - holder 14 with spring 16 - is installed on roller 15 of the KPE rotor, after which the operation of the vernier as a whole is checked.
The front wall 1 is fixed to the chassis wall with 26 screws and nuts, and to the plate 5 - with screws screwed into the bar 11.
Rice. 2. View of the docking unit of one of the options for the practical design of the vernier with the KPI
Part materials and some technological instructions for assembling the vernier are contained in the caption under fig. 1. A view of the docking unit of one of the options for the practical design of the vernier with the KPI is shown in fig. 2.
Author: S. Dolganov
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