How to make a vernier for a radio. Vernier for kpe. Air condenser device - variable capacity

Dear visitors!!!

Radio receivers differ in their design and the way they tune to the frequency of the received signal. That is, the setting can be carried out either by a vernier device \to search for the required frequency\, or the frequency search can be performed with a light touch of a finger - with a control panel, which is a separate block diagram\touch control\.

Vernier device-radio receiver

Figure 1 shows the simplest kinematic diagram of the vernier device. This device is familiar to all of you. The search for setting the required frequency is carried out by rotating the wheel / axis of the tuning knob /. Between the guide wheels, and there are three of them in this scheme, a nylon thread is stretched - in the engagement of which there is a pulley. To make it more clear, in an illustrative example, a photograph of this device is given.

Vernier device of the radio receiver

Due to the rotation of the pulley, the KPE plates are set in motion. In schemes for radio receivers, there is such a name as the KPE block. The KPE block is a variable capacitor with an air dielectric.

Similar capacitors are found:

with a one-section block;

two-section block;

three section block.

two-section block KPE

three-section block KPE

Such radio components are well known to you, they are found both in obsolete models \ USSR radios \, and in modern models radio receivers. In modern models, the KPI blocks are more advanced, as is the design of the receivers themselves, and have small overall dimensions.

Air condenser device - variable capacity

Suppose, if we take for example a two-section block \Fig.2\, this device consists of two capacitors. Accordingly, to designate this radio component, its own graphic image\indicated above, fig.2\. Already, if you read the radio circuit yourself, you will know that the graphic designation in the circuit, as shown in the figure, is a two-section variable capacitance block with an air dielectric.

Capacitor designation

If, for example, the value for KPI is found in the radio circuit - C40 9 ... 365, then the radio amateur will already be able to say that this capacitor has a serial number - 40, and the variable capacitance at a full turn of the rotor is from 9 to 365 picofarads.

Here it should also be learned that a variable capacitor with an air dielectric \KPE\ consists of a movable and a fixed part. The movable and fixed parts consist of a certain number of aluminum plates. The movable part of the plates is called the rotor, the fixed part is called the stator.

You should remember two graphic symbols \Fig.3\ and do not confuse them, where indicated:

designation of a variable capacitor \with an air dielectric\;

trimmer capacitor designation,

- the required capacity of which is set by adjusting, - with a flat screwdriver. Adjustment for the tuning capacitor is carried out by specialists at the factory, when the nominal value of the capacitance is established. But when it comes to personal ingenuity, then such changes are made by ourselves radio amateur.

So, friends, I am directly with you entering the world of interesting and identifiable things, so to speak, I recall my former hobby. Follow the rubric, further will be even more interesting.

Today I continued to make vernier parts. He took out a pile of paper until he figured out how best to do it all.
From the pulley you need to make an entrance and exit for the cable. The exit will be "far". So that the threads do not intertwine, I drilled a 2 mm hole at an angle of 30 degrees so that it would come out near the far side. This will be the outlet for the cable. At the second exit of the hole, I milled the platform to the plex, drilled a hole and cut the M3 thread. I screwed in a screw with a small rack. The end of the cable will be tied here, and the washer will prevent it from jumping off.

In the photo - the design of the "exit" for the cable.

With the "entrance" it is somewhat more difficult - you need to install a spring, which will select the "slack" of the cable. But this problem was also solved. I milled a groove slightly wider than the diameter of the spring, as well as a platform, in the center of which I cut an M3 thread and screwed in a screw with a through hole in the cap.

In the photo - the design of the "entrance" for the cable.

The next part is the flywheel assembly. He took a very long time with him. There was a flywheel from "Latvia", but its design did not suit me. I had to completely redo it. I also found a suitable plain bearing, but it has a round body with a diameter of 16 mm. That was the main problem with him. How it was fixed - can be seen in the photo.

The photo shows the details of the flywheel assembly and its "assembly drawing".

The assembly is visible in the second photo (from bottom to top): locking sleeve, getinax washer, bearing assembly, mounting pad, fluoroplastic washer, flywheel.
The result is this:

Pictured is the flywheel assembly.

After that, I marked the attachment points of the nodes on the false panel, installed them, adjusted them and tried to assemble the mechanism. To do this, I used a simple, harsh thread (it's a pity for the cable!). The result is such a "mechanism":

In the photo - a trial assembly of the vernier mechanism.

On the flywheel axis, I fixed the cable rotation unit from the Latvian VHF unit. I had to shorten it, and since it is made of a very fragile silumin, I used a steel band to fix it on the flywheel axis. In the silumin, I only drilled a through hole for the retaining screw of the bandage.

In the photo - the axis of adjustment.

In the photo, the fastening of the manufactured nodes on the false panel.

After adjusting and lubricating the mechanism, it worked quite well. The axis rotates smoothly, with a slight resistance pleasant for the hand. The surrogate arrow moves smoothly, does not jam anywhere, the thread does not “bite” anywhere and does not jump off. In general, I was satisfied.

Again, "smart thought", which "comes after" ...

Already when the mechanism was working, it dawned on me that a rather strong lateral load would be constantly applied to the axis of the variable resistor. It "came" because I saw that the pulley was slightly "skewed" inside the future scale. Shaking it lightly with his hand, I saw that the backlash of the axis of the variable resistor is quite large. This is on the KPI, with its rolling bearing!
Those. you need to redo this assembly - install a "condo" axis with its own bearing, and somehow flexibly connect the axis of the variable resistor with it. Something like this (what was at hand).

Despite the possibility of acquiring factory-made transceiver equipment, some shortwave radio amateurs are still engaged in the manufacture, design and development of home-made equipment for amateur radio communications.

One of the important elements of the transceiver (receiver, transmitter) is the tuning unit for the operating frequency. At present, tuning with a variable capacitor is still widespread. But with such a tuning, a relatively complex mechanical vernier device is required, providing a frequency tuning density of no more than 50-60 kHz per one turn of the tuning knob. This density of restructuring is most comfortable when working on the air.

Less common is the tuning node, which uses a varicap controlled by an adjustable voltage. direct current. This tuning method simplifies the circuitry and design of the tuning unit due to the absence of mechanical parts.

To control varicaps, special wire-wound adjustment resistors of several less common types are usually used. For example, resistors SP5-35 and SP5-40A, the electrical circuit of which is shown in Fig. 1, are made according to the scheme with two resistive elements. In this case, both mobile systems are controlled from one shaft. When adjusting the resistance, first the movable system of the "fine" resistive element is rotated from stop to stop, and then the movable system of the "coarse" resistive element is rotated.

An additional variable resistor can be connected to the movable system of the "accurate" resistive element SP5-40A, consisting of two disconnected contact springs, which can significantly improve the resolution of the main resistor.

In addition, for such tuning nodes, variable wire resistors SP5-39 and SP5-44 are used - ten-turn, with a spiral resistive element. If the first group has a wear resistance of 5-10 thousand cycles, then the second - from 500 to 5000 cycles (depending on the type of resistor), which is clearly not enough for the tuning nodes that are constantly in operation.

Currently, varicap tuning in combination with built-in digital scales is very convenient and affordable. technical solution. However, these properties of multi-turn control resistors limit the use of this tuning method. The use of conventional single-turn variable resistors with a shaft rotation angle of 270 degrees, which obviously have a high wear resistance, leads to a deliberately unacceptable frequency tuning density and, accordingly, to certain inconveniences when working on the air.

In B, a double-adjustment potentiometer circuit was described, composed of a double and a single variable resistor (Fig. 2), suitable for obtaining regulated voltage both with low resolution from one shaft and with increased resolution from the other shaft. "Stretching" is subjected to a voltage interval equal to half the input, which is not always sufficient. Of course, dual variable resistors are available with different resistances of the resistive elements. In extreme cases, you can replace the resistive element with another one, which is facilitated by standard sizes variable resistors. But this is due to the need to fulfill the corresponding installation work which is not always acceptable or possible. In a word, the use of a dual variable resistor does not provide a sufficiently large resolution of the tuning node, and the dual variable resistor itself is not the most common and accessible element.

This principle of obtaining an adjustable constant voltage with two separate controls with different functional properties is the most accessible for use in various designs. However, it is complicated by the fact that it is necessary to use a double variable resistor, preferably with a concentric arrangement of shafts and separate control: for coarse tuning, two resistors are controlled by an external shaft, for fine tuning, one resistor is controlled by an internal shaft. Such a technical solution is not common enough and affordable for an ordinary radio amateur, especially one living in the outback.

To eliminate this shortcoming, it is proposed to use a current summation circuit with similar functional properties (Fig. 3), which uses two single-turn variable resistors.


The deceleration coefficient is determined by the ratio of the resistances of the resistors R2/R1 and can be chosen practically by any, since with an increase in the deceleration coefficient and, accordingly, with an increase in the resolution, the range of regulated voltages by the second shaft, which regulates with high resolution, decreases. Figure 3 shows the resistances of the resistors that provide a deceleration ratio of 1:10.

The proposed technical solution opens up the widest possibilities for choosing the desired tuning density using the second shaft, and it is actually possible to obtain quite acceptable tuning density and tuning range width. At the same time, the ratios must be observed - R1>=10RP1, R2>=10RP2. And since a deliberately smaller current is taken from the RP2 engine circuit, the resistance of the RP2 potentiometer can be chosen much larger than the resistance of the RP1 potentiometer.

The proposed scheme is also convenient in that it is not critical to the choice of resistances of variable resistors. To obtain a linear adjustment in the circuit, variable resistors of group A should be used with a linear dependence of the resistance on the angle of rotation of the shaft.

In some cases it may be useful diagram(Fig. 4) with a variable deceleration coefficient, changing from an infinitely large "below" (in the tuning node, the frequency change will be minimal) to a minimum "above" (the frequency change is maximum). Here, the deceleration coefficient is determined by the ratio of the resistance of the resistor R2 to the resistance between the RP1 engine and the common wire. Thus, at each position of the RP1 slider, a certain deceleration coefficient takes place.

If a radio amateur has the opportunity to use a dual variable resistor with concentrically located shafts and, accordingly, separately controlled individual resistors, then it is possible to make an almost analogue of a conventional vernier device. True, with a limited range of smooth tuning and two tuning controls located on the same axis, which is more convenient than two tuning knobs located next to each other.

This technical solution allows the use of varicap tuning in equipment of a higher class than the simplest designs for beginner radio amateurs, since it provides ease of execution, reliability during long-term operation and ease of use in operational work. The design of the tuning unit was tested in a single-band transceiver for a range of 80 m. The coarse frequency tuning range was slightly more than 300 kHz, the smooth tuning range was approximately 7-10 kHz.

The proposed technical solution can be used not only in transceiver equipment, but also in DC signal sources, power supplies, and wherever required smooth adjustment DC or AC voltage with high resolution.

Literature

1. D. Dzhemella. Double adjustable potentiometer. - Radio, 1965, No. 2, p.43
2. Resistors: a reference book. 2nd ed. revised and additional - M.: Radio and communication, 1991.
3. E. Solodovnikov. Source of direct current signals. - Radio amateur, 1999, No. 10, p. 36-37.

Publication source: Radiomir: HF and VHF, 2007, No. 7, p.25-27

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
stuffy 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 external
with a diameter of 7 mm (the author used a telescopic antenna knee), 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 cutting thread 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 with 11 screws 3x20, 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 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 final assembly 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.

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. body of the radio receiver 1), on the other - a coupling connecting it to the shaft 15 of the KPE rotor, consisting of two holders 14 and flat springs 16 and 17 fixed to them with screws 9. This mechanism assembly is designed to compensate for misalignment of the shaft 8 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 ream up desired diameter well-sharpened drill. 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 4, 18 and corners 24 are screwed to plates 5 and 20, and holder 13 to disk 12 (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 12 is inserted into the gap between the disks 27 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 2 on the end of the roller 3 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 7 on roller 8 with arrow 10 pre-fixed on it with screws 9 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.

The vernier device is understood as a mechanical drive from the tuning knob to the tuning body of the radio receiver, which allows the radio listener to tune in to the broadcasting station. The vernier device is the main operational control of the radio receiver, so it must be reliable in operation under any operating conditions. There are various designs of vernier devices: gear, worm, friction, gears with a flexible thread, etc.

Their structural difference lies in the different mechanical complexity and manufacturing accuracy, and hence the cost. The most simple

and a cheap vernier design is the flexible filament deceleration mechanism which is widely used in broadcast receivers. The mechanical drive from the tuning knob to the variable capacitor (CPE) and the VHF unit is carried out in these cases using a flexible cable. True, when the vernier device has a large gear ratio, which is structurally impossible to carry out with a transmission with a flexible thread, a gear transmission is additionally introduced, usually installed on the KPE block. It should be noted that the vernier device with a deceleration mechanism with a flexible thread is less accurate than other gears used. This is explained by the fact that the flexible connection does not have sufficient rigidity, therefore, during operation, “dead running” and stretching of the flexible thread may appear, which have to be compensated by introducing additional mechanical devices. However, despite the fact that flexible thread transmissions have significant drawbacks, they are the main vernier system of broadcast receivers, used mainly for economic reasons. On the other hand, the choice of this transmission system is justified by purely constructive considerations and less stringent requirements for the accuracy of the performance of the reading (scale) devices of broadcasting receivers.

The structural advantage of the vernier device with a flexible thread is that this mechanical system allows you to place the scale of the radio receiver in almost any spatial position. The scales in this transmission system can be carried out without design difficulties. large sizes, for example, may occupy most of the front surface of the radio housing. This circumstance is essential for broadcasting receivers, since it is technologically easier to apply indicator divisions, inscriptions and digital designations on large scales. At the same time, the scale becomes more visual and easier to read by its radio listener. Accuracy

the application of indicator divisions on scale broadcasting receivers is ±0.2 mm, which is much lower than in special equipment. For example, the accuracy of the arrangement of strokes on the scale of the radio receiver of special equipment reaches 0.005 mm. In turn, the relatively low accuracy of the scale simplifies the technology of its manufacture and, consequently, reduces the cost.

Let us consider in what ways the requirements for vernier devices in transmission systems with flexible communication are fulfilled. The main requirements for vernier devices are smooth tuning and backlash-free transmission.

Tuning smoothness refers to the amount of movement of the tuning knob (in millimeters or angular degrees) to change the tuning frequency by 1 kHz.

In broadcast receivers, the permissible error during tuning is assumed to be ± 1 kHz.

Thus, according to the given smoothness of tuning, the vernier transmission of the radio receiver is calculated.

The gear ratio of the vernier device is determined depending on the class of the radio receiver. GOST 5651-64 "Broadcast receivers" indicates the frequencies and wavelengths that are used in broadcast receivers (Table 2).

table 2

Range name	Frequency, kHz	Wavelength, m
Long waves	150-408	2000-735,3
Medium	525-1 605	571,4-186,9
Short	3590-12 100	75,9-24,8

However, not all classes of broadcast receivers use the above ranges. For example, in broadcasting receivers of classes III and IV, in order to reduce the cost of their design, it is not recommended to use the shortwave range.

The calculation of the gear ratio of the vernier device is carried out in the following sequence.

Knowing that the angle of rotation of the variable capacitor (KPI) is 180 °, the angle of rotation is determined at which the tuning error will not exceed ± 1 kHz or the absolute error will not exceed 2 kHz. Then for long waves the absolute error of 2 kHz will be V129 part of the range 408 - 150 = 258 kHz; for medium waves - V540 part of the 1080 kHz band and for short waves V4075 part of the 8.15 MHz band.

Consequently, the angle of rotation of the variable capacitor (KPI) with an absolute error of 2 kHz will be: for long waves 180°/129 == = 1.4°, medium waves 1807540 = 0.33° and short waves 18074075 = 0.043°.

Considering that an average-skilled tuner is able to set the rotation angle with an accuracy of 1 -1.5 °, it is obvious that in the medium and short wave ranges it is impossible to tune the radio receiver with a given accuracy without introducing a slow vernier transmission.

It is quite natural that the tuning of broadcasting receivers designed for the mass consumer is carried out by any radio listener, regardless of his specialty and qualifications. For these reasons, a large angular error is allowed on the tuning knob, the value of which can be in the range from 2.5 to 3.5 °.

From the ratio of the angular error on the tuning knob to the permissible angular error on the variable capacitor, the gear ratio of the vernier gear is determined. Thus, for medium waves, the gear ratio of the vernier mechanism, to ensure tuning accuracy of ± 1 kHz, should be in the range of 7.6-10.6, and for short waves 58-81.5.

It is acceptable to choose large gear ratios, however, it is undesirable to increase the number of turns of the tuning knob to cover the entire range by more than 15, since in this case the tuning time to the broadcasting radio station is lengthened, which causes operational inconvenience. Usually small gear ratios are used in class III and IV radio receivers, and large gear ratios are used in higher

class. It is not recommended to choose gear ratios less than 7.6-10.6, since the mechanical transmission coefficient decreases, and tuning by the receiver ranges becomes inaccurate and rough.

From the above calculations, one can imagine the design of the vernier mechanism. For example, for radio receivers of classes III and IV, which do not have a short wave range and the gear ratio does not exceed 10.6, it is advisable to install the drum directly on the axis of the variable capacitor. For radio receivers of the highest, I and II classes, it is necessary to introduce an additional slowdown transmission between the drum and the variable capacitor.

The final gear ratio of the vernier mechanism is determined by design considerations.

The overall structural layout of the radio determines the dimensions of the chassis, the installation of the main blocks, the location of the loudspeaker and the length of the scale. After agreement appearance radio receiver with designers, who usually present sketches of the external design of the receiver, the dimensions of the scale are finally determined, and, consequently, the desired course of the index arrow.

It may turn out that, according to constructive calculations, it is possible to increase the course of the index arrow, and, consequently, the scale of the radio receiver. For example, in radiograms I and the highest class, the index arrow stroke reaches 250 mm.

Knowing the course of the index arrow and the angle of rotation of the KPI rotor, it is possible to determine the gear ratio of the vernier mechanism. Depending on the class of the designed radio receiver, we set the appropriate number of revolutions of the handle and, for structural reasons, the diameter of the axis.

If the drum diameter d1 = L/3.14 turns out to be too large for the designed structure, it is reduced to the required dimensions. In this case, the number of revolutions of the drum naturally increases.

Knowing that the rotation of the variable capacitor rotor is 180 °, that is, the rotor rotates 72 turns, the gear ratio from the drum to the rotor axis will be i = n1 / n2, where n 2 is the number of revolutions of the capacitor rotor.

The ratio of the number of gear teeth and wheel is defined as i=Z2/z1.

The number of gear teeth z1, which is mounted on the drum, is determined by technological and design considerations. Moreover, the smallest allowable number of teeth is selected according to a certain Z1 and i and the gear wheel z2 is calculated. Further calculation of gears goes in the usual way according to the formulas given in many reference books and technical literature.

The second requirement for vernier devices, the backlash-free transmission in mechanical systems with a flexible thread, is performed using tension springs, rollers and split gears. The main reason for the appearance of backlash in the mechanical transmission is the occurrence of residual deformation of the thread during the operation of the vernier device. ego phenomenon in more affects when used as a flexible thread kapron cord. Therefore, in production conditions, in order to reduce the residual deformation of the nylon cord, it is specially pulled out with a load for some time before being installed in the vernier cord. mechanism. The elimination of backlash in the vernier transmission in broadcasting receivers is carried out by the same devices that are used to create tension in a flexible thread. On fig. 27 shows various kinematic diagrams of devices that create thread tension.

The tension system shown in fig. 27, vg is the most appropriate from the point of view of simplicity of design, since the thread tension force is created by one tension spring.

On fig. 27, d shows one of the most common thread tension systems. The tension spring is installed inside the drive drum. The force of the tension spring is slightly more than 2Pt, since the friction of the thread on the surface of the drum should be taken into account.

Thus, the systems shown in Fig. 1 are simpler in design. 27, wig, of which the d system is recommended for use, since in all vernier devices a drive drum is used, which in this case is used simultaneously for attaching the tension spring.

In some cases, due to the small size of the scale device or the small diameter of the drive drum, the whig systems may not be suitable, therefore, when choosing one or another system, it is necessary to be guided by design considerations, determining which of the systems is most consistent with the overall design of the vernier device. At the same time, it is necessary to take into account the simplicity of the design and, consequently, its cost.

In cases where it becomes necessary to apply an additional slowdown gear to the variable capacitor unit, it is performed using backlash-free or “split” gears (Fig. 28). The shift of the teeth of the driven gears is carried out by a spring, which selects the gap between the teeth that appears when they are connected to the drive gear. It must be borne in mind that the moment that the spring creates to shift the gears should be approximately 1.5 times the torque. The gear module in the vernier device is used from 0.75 to 1.5, since gears with these modules are made without technological difficulties

by stamping or pressing. Such means fulfill the basic requirements for vernier devices.

Rice. 28. Designs of split gears.

Two types of vernier devices with flexible coupling are used in broadcasting receivers: two- and one-wire systems. Depending on the class of the radio receiver, and, consequently, on its cost, one or another vernier transmission system is selected. In the case when the radio receiver must receive radio transmissions along the path of amplitude modulation and frequency modulation, as a rule, a two-cable vernier transmission is selected. In this case, separate tuning is carried out along the amplitude modulation path and the frequency modulation path. The single-cable vernier transmission system is mainly used in cheap class IV radio receivers, in which the range of received frequencies is limited by the amplitude modulation path.

Rice. 29. Kinematic diagram of a two-cable vernier transmission.
1 - drum block K.PE; 2- cable tract AM; 3 - index arrow; 4 - tension spring; 5 - vernier gears; 6 - KPE block; 7 - guide roller; 8 - drum unit VHF; 9 - cable of the FM tract; 10 - tension roller; 11 - AM path tuning axis; 12 - FM tract tuning axis.
On fig. 29 shows a kinematic diagram of a two-cable vernier transmission.

As can be seen from fig. 29, a two-cable vernier device consists of two soft-link transmissions, one of which is designed to be tuned along the amplitude modulation path, and the second - along the frequency modulation path. In this case, the transmission along the amplitude modulation path has a slow gear transmission from the drum to the KPI block to increase the gear ratio. The cable tension is created
coil spring mounted on the drum. In the vernier transmission to the VHF unit, the cable tension is created by a tension roller. On the depicted kinematic diagram, tuning along the path of amplitude modulation and frequency modulation is carried out from two separate knobs.

There are other designs, when instead of two tuning knobs one is used, and switching to the AM and FM paths is carried out using the couplings shown in Fig. 30. The designs of these couplings are widely used in Philips broadcasting receivers. In this case, switching along the AM and FM paths is carried out by moving the clutch using a rocker arm to the right and left bushings. Both bushings sit freely on the tuning axis and enter into rigid engagement with the axis when the coupling is pressed against the rubber washer. The movement of the clutch is made from the rocker, which, in turn, rotates from the levers of the main range switch. For reliable engagement of the bushing with the movable coupling, spikes are installed on its surfaces, which, when the coupling is pressed against the bushing, cut into the rubber washer. The cables of the vernier gears are mounted on the recesses of the bushings. In the area of ​​the clutch, the tuning axis is made flat.

Rice. 30. Philips coupling.
1 - tuning axis; 2 - bushing; 3 - rubber washer; 4 - mobile clutch; 5 - rocker.

On fig. 31 shows the second type of couplings. Switching cable systems to one or another path of the radio receiver in this design is carried out by mechanically fixing the bushings with the tuning axis. Both bushings 2 sit freely on the axis, and their movement along the axis is limited by thrust washers 4. Limiter 5,

made in the form of a bar with a hole for the pin 7, rigidly fixed on the axis. The bar 6 sits freely on the axis 1, but is rigidly connected to the pin 8, which, in turn, is inserted into the stem 9.

The movement of the rod 9 is carried out from the levers of the main range switch. When the rod 9 moves to the left, the bar 6 moves, and the pin engages with the washer 3 pressed on the left sleeve. Washer 3 has several notches for engagement with pin 7. When turning the axis, pin 7 always falls into the notches of washer 3, since the moment

the friction of the pin on the surface of the washer is much less than the moment of rotation of the tuning axis. With the free position of the rod 9, the right sleeve enters into mechanical engagement with the axle.

On fig. 32 shows a single cable vernier transmission system. This transmission system is very simple and is mainly used for class IV radios, which do not have a short wave and VHF band. Therefore, this vernier transmission has a small gear ratio and does not require the introduction of additional deceleration on the KPI block. The drum, on which the cables are attached, is installed directly on the axis of the KPE block. Sometimes a single-cable transmission, in order to simplify the kinematic system of the vernier device, is also used in class III radio receivers, for which, according to GOST 5651-64, the VHF range is mandatory.

Rice. 31. Philips coupling.
1 - tuning axis; 2-sleeve; 3 - curly washer; 4-thrust washer; 5-limiter;
6-movable washer; 7- pin; 8 - hairpin; 9- stock; 10-spring.

Rice. 32. Kinematic diagram of a single-cable vernier transmission.
1 - drum of the KPE block; 2- cable;
3- index arrow; 4 tension spring; 5-drum block VHF; b - tuning axis; 7 - guide roller.

The main disadvantage of a single-cable system, when used in radio receivers with a VHF unit, is that when tuning along the AM path, the inductor device of the VHF unit is inevitably set in motion, and vice versa, when tuning along the FM path, the KPI unit receives rotational motion, since these blocks are mutually mechanically connected. Naturally, in this system, the moving elements of the tuning blocks wear out more than in the two-cable system, and, consequently, the reliability of the operation of the entire vernier device decreases. From the above example, it can be seen that it is not in all cases advisable to simplify the design in order to obtain an economic gain, since this issue cannot be resolved in isolation from other requirements for a broadcast receiver, for example, reliability.

The direction of movement of the cables in the vernier device is determined by the guide rollers mounted on the soffit of the radio receiver chassis or on special brackets. Although the cost of guide rollers is a small part of the total cost of a radio receiver, the design should pay attention to the economics of their manufacturing technology. The rollers themselves are usually made of plastics.

On fig. 33a shows the simplest method of manufacturing and fixing the roller axis; the axle itself is produced by centerless grinding and pressed into an extrusion, which is carried out in sheet material. On fig. 23b, the axis is made by turning and fastened by flaring. On fig. 23, b shows the fastening of the roller axis, made by mechanical compression of the metal, but the axis itself in this case is less technologically advanced than previous designs.

On fig. 34 shows three ways to fasten the guide rollers on the axles: using a thrust washer, selected depending on the diameter of the axle along the NO normal. 894.007 (Fig. 34, a); using a spring washer (Fig. 34, b), which does not require the manufacture of grooves on the axle (this method is convenient for axles made by centerless grinding); using a hollow rivet, mechanically crimped on the roller axis (Fig. 34, c).

The index arrows of the radio receiver, as a rule, are attached directly to the vernier transmission cable. On fig. 35 a, b, c shows various designs of pointer arrows and methods for their fastening.

When designing a vernier device, first of all, the gear system is calculated

transmission. Depending on the class of the radio receiver, the required gear ratio of the vernier device is determined. Then a preliminary layout is already carried out, according to which structural elements, the course of the pointer, the length of the scale, the design of the tension roller system, etc. The flexible connection performed by the cable transmission should not have sharp bends, since in this case the movement of the cable is difficult, which leads to its premature wear.

Rice. 35. Designs of index arrows.

The structural complication of the vernier transmission due to the introduction of additional elements (for example, couplings) that increase operational convenience is advisable only in radio receivers of the highest classes. In radio receivers of classes III and IV, one should strive to maximally simplify the kinematic scheme of the vernier device.

In broadcast receivers, the scale is graduated in kilohertz and meters. The determination of the position of a broadcasting radio station is made by the magnitude of the wavelength. The wavelength value is graduated on the scale from left to right, upwards.

For capacitive tuning, when the indicator needle is at the beginning of the scale, i.e., indicates the minimum wavelength or maximum frequency, the capacitance of the variable capacitor must be minimal. The rotor plates must be brought out of the capacitor stator. In VHF units

with inductive adjustment, when the tuning rod is made of non-magnetic material, for example, brass, the position of the indicator arrow at the beginning of the scale corresponds to the fully inserted tuning rod. According to these considerations, the direction of movement of the cable and, consequently, the indicator arrow is determined. In accordance with the requirements of engineering psychology, it is considered most convenient to rotate the tuning knobs in the direction of the indicator arrow movement.

In correctly designed vernier devices, the amount of torque on the tuning knob of the broadcasting receiver does not exceed 120 Gcm.

The axles on which the drive cable is wound are made with a diameter of 3 to 10 mm. It is undesirable to use small diameters, since in these cases the friction between the cable and the axle is insufficient, which leads to the cable slipping on the axle during radio operation. The most convenient axles for work have diameters of 6-10 mm.

According to the known Mvr and R, we find that the force on the cable should not exceed 300 G. To ensure a reliable mechanical connection of the cable with the drive axle, 1.5-2 turns are sufficient. A large number of turns adversely affects the operation of the vernier device. This is due to the fact that due to the rotation of the axis both clockwise and counterclockwise, with a large number of turns of the cable wound on the tuning axis, one turn runs over the other and the entire transmission system is jammed. It is also not recommended to increase the torque on the tuning knob, since in this case the tension of the cable increases, and consequently, its operational reliability decreases, the wear of the elements of the kinematic

vernier system, the ease of movement of the index arrow is deteriorating.

The ease of movement of the index arrow is one of the advantages of the broadcast receiver. In radio receivers of the highest, I and II classes, special attention is paid to this issue. To facilitate the movement of the pointer, a handwheel is installed on the axis of the tuning knob, the mass of which allows, from a slight rotational movement of the handle, to ensure free accelerated translational movement of the pointer along the scale of the receiver. Handwheels are usually made from aluminum alloys or stamped from thick sheet steel.

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