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 are tuned to the frequency of the received signal. That is, tuning can be carried out either by the vernier device \\ to search for the required frequency \\, or the frequency search can be performed with a light touch of the finger of the hand - with the control panel, which is a separate block diagram \\ touch control \\.
Vernier radio receiver
Figure 1 shows the simplest kinematic diagram of the vernier device... This device is familiar to you all. 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 which the pulley is engaged. To make it more understandable, in an illustrative example, a photograph of this device is given.
Radio vernier device
Due to the rotation of the pulley, the KPE plates are set in motion. In the circuits for radio receivers, there is such a name as the KPI unit. The KPE unit 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 KPE block
Such radio components are well known to you, they are found both in obsolete models \\ radio receivers of the USSR \\ and in modern models radio receivers. In modern models, KPE units are more improved, as well as the design of the receivers itself and have small overall dimensions.
Air Condenser Device - Variable Capacity
For example, if we take a two-section unit \\ Fig. 2 \\, this device consists of two capacitors. Accordingly, to designate a given 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 block of variable capacity with an air dielectric.
Capacitor designation
If, for example, the value for KPI is C40 9 ... 365 is found in the radio circuit, 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 rotor revolution is from 9 to 365 picofarads.
It should also be learned here that a variable capacitor with an air dielectric \\ KPE \\ consists of a movable and a fixed part. The movable and stationary parts consist of a certain number of plates \\ aluminum \\. The movable part of the plates is usually called the rotor, the stationary \\ fixed \\ part is the stator.
You should remember two graphic symbols \\ Fig. 3 \\ and do not confuse them, where it is indicated:
variable capacitor designation \\ with air dielectric \\;
the designation of the trimmer capacitor,
- the required capacity of which is set by adjusting, - with a flat screwdriver. The adjustment for the trimmer 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 identifying, so to speak I remember my past hobby. Follow the rubric, it will be even more interesting further.
Today I continued to manufacture vernier parts. I ran through a pile of paper while I 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 "distant". To prevent the threads from intertwining, 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 exit for the cable. At the second exit of the hole, I milled the platform to the plexus, drilled a hole and cut the M3 thread. Screw in a screw with a small stand. The end of the cable will be tied here, and the washer will prevent it from jumping off.
The photo shows the design of the "exit" for the cable.
With the "entrance" it is a little more difficult - you need to install a spring, which will choose 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 head.
In the photo - the construction of the "entrance" for the cable.
The next detail is the flywheel assembly. I spent a very long time with him. There was a flywheel from "Latvia" available, but its design did not suit me. I had to completely redo it. A suitable sleeve bearing was also found, but it has a round housing with a diameter of 16 mm. That was the main problem with him. How they managed to fix it - you can see in the photo.
The photo shows details of the flywheel assembly and its "assembly drawing".
The assembly is visible in the second photo (from bottom to top): lock bushing, getinax washer, bearing assembly, mounting pad, PTFE washer, flywheel.
The result is this:
The photo shows the flywheel assembly.
After that, I marked the attachment points of the knots on the false panel, installed them, adjusted them and tried to assemble the mechanism. For this I used a simple harsh thread (a pity for a cable!). The result is such a "mechanism":
The photo shows a trial assembly of the vernier mechanism.
On the flywheel axis he fixed the cable rotation unit from the VHF unit "Latvia". I had to shorten it, and since it was made of a very fragile silumin, I used a steel band to fix it on the flywheel axis. In silumin, I just drilled a through hole for the retaining screw of the bandage.
The photo shows the tuning axis.
The photo shows the fastening of the manufactured units on the false panel.
After adjustment and lubrication, the mechanism worked quite well. The axis rotates smoothly, with little resistance, pleasant for the hand. The surrogate arrow moves smoothly, does not bite anything anywhere, the thread does not "bite" anywhere and does not jump off. In general, I was satisfied.
Again "smart thought", which "comes after" ...
Even when the mechanism was working, it dawned on me that a fairly strong lateral load would be constantly applied to the axis of the variable resistor. It "got" because I saw that the pulley was slightly "skewed" inside the future scale. Shaking it lightly with my hand, I saw that the backlash of the axis of the variable resistor is quite large. It's on the KPI, with its rolling bearing!
Those. it is necessary to remake this unit - to install the "kondovaya" axis with its own bearing, and the axis of the variable resistor is somehow flexibly connected to it. Something like this (what was at hand).
Despite the possibility of acquiring factory-made transmitting and receiving equipment, some shortwave radio amateurs are still engaged in the manufacture, design and development of homemade equipment for amateur radio communications.
One of the important elements of the transceiver (receiver, transmitter) is the tuning unit to the operating frequency. Tuning with a variable capacitor is still widely used today. 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. Such tuning density is most comfortable when working on the air.
A less common tuning unit that uses a variable voltage controlled varicap 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 control resistors of several less common types are usually used. For example, the resistors SP5-35 and SP5-40A, the electrical diagram of which is shown in Fig. 1, are manufactured according to a circuit with two resistive elements. In this case, both moving systems are controlled from one shaft. When adjusting the resistance, the movable system of the "precise" resistive element first turns from stop to stop, and then the movable system of the "rough" resistive element rotates.
An additional variable resistor can be connected to the moving system of the "exact" resistive element SP5-40A, which consists of two disconnected contact springs, which significantly improves 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 durability 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 constantly operating tuning nodes.
At present, varicap tuning in combination with built-in digital scales is a very convenient and affordable technical solution. However, these properties of multi-turn adjusting 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 are known to have high wear resistance, leads to a deliberately unacceptable frequency tuning density and, accordingly, to certain inconveniences when working on the air.
C was described a double adjustable potentiometer circuit composed of dual and single variable resistors (Fig. 2), suitable for obtaining regulated voltage with both low resolution from one shaft and high resolution from another shaft. A voltage interval equal to half the input voltage is subjected to "stretching", which is not always sufficient. Of course, dual variable resistors are available with different resistances. As a last resort, you can replace the resistive element with another, which is facilitated by standard sizes variable resistors. But this is due to the need to fulfill the appropriate installation works, which is not always acceptable or possible. In a word, the use of a double variable resistor does not provide a sufficiently high resolution of the tuning unit, and the double variable resistor itself is not the most widespread and accessible element.
This principle of obtaining an adjustable constant voltage with two separate controls with different functional properties is the most readily available 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 adjustment, two resistors are controlled by an external shaft, for precise adjustment, one resistor controlled by an internal shaft. Such a technical solution is not widespread enough and affordable for an ordinary radio amateur, especially one living in the outback.
To eliminate this drawback, it is proposed to use a current summation circuit with similar functional properties (Fig. 3), in which two single-turn variable resistors are used.
The deceleration coefficient is determined by the ratio of the resistances of the resistors R2 / R1 and can be chosen almost anything, 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 resistors for a 1:10 deceleration ratio.
The proposed technical solution opens up the widest possibilities for choosing the desired tuning density using the second shaft, and in fact it is possible to obtain quite acceptable tuning density and tuning range width. In this case, the ratios - R1\u003e \u003d 10RP1, R2\u003e \u003d 10RP2 must be observed. And since a deliberately lower current is taken from the RP2 engine circuit, the resistance of the RP2 potentiometer can be chosen significantly larger than the resistance of the RP1 potentiometer.
The proposed circuit 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 resistance on the angle of rotation of the shaft.
In some cases, it may be useful diagram (Fig. 4) with a variable deceleration coefficient varying from an infinitely large "bottom" (in the tuning unit, the frequency change will be minimal) to a minimum "above" (frequency change is maximum). Here the deceleration factor 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, there is a certain deceleration ratio.
If the radio amateur has the opportunity to use a double variable resistor with concentrically arranged shafts and, accordingly, separately controlled separate 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 adjacent tuning knobs.
This technical solution allows the use of varicap tuning in equipment of a higher class than the simplest designs for novice radio amateurs, since it provides simplicity of execution, reliability during long-term operation and ease of use in operational work. The tuner design was tested in a single-band transceiver for 80 m. The coarse frequency range was slightly more than 300 kHz, and the sweep range was approximately 7-10 kHz.
The proposed technical solution can be used not only in receiving and transmitting equipment, but also in DC signal sources, power supplies, and also wherever smooth regulation of DC or AC voltage with high resolution is required.
Literature
1. D. Gemella. Potentiometer with double adjustment. - Radio, 1965, No. 2, p.43
2. Resistors: a reference book. 2nd ed. revised and add. - M .: Radio and communication, 1991.
3. E. Solodovnikov. Source of DC signals. - Radio amateur, 1999, No. 10, p. 36-37.
Publication source: Radiomir: KV 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 tuner (for example, the KPE rotor) at a relatively small angle. For the successful performance of 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 a
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 case 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 with a thickness of 6 mm, you can use organic glass or polystyrene of the same thickness), 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 the knee of a telescopic antenna), epoxy glue and standard fasteners (M3 screws and nuts, several self-tapping screws and screws), and from tools - a hacksaw for metal, 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 disc, consisting of two glass fiber laminate discs glued together, the same number of washers 28 and a spacer 29, is glued to the roller 3, on the left (according to the figure) end of which the adjustment knob is fixed 2. The roller rotates in bearings 4 and 18, screwed to the plates 5 and 20, which, in turn, are fixed on the chassis of the receiver 26. The movement of the roller in the axial direction is prevented by the washers 22 put on it and the pins 21 pressed during assembly.
Figure: 1. The device of the friction vernier: 1 - the front wall of the receiver body, fiberboard, fasten to the bar 11 with 3x20 screws, and to the chassis 26 - with 23 screws with nuts 25; 2 - adjustment knob; 3 - roller of the driving disk, brass tube (knee of the telescopic antenna); 4 - bearing 1, fiberglass with a thickness of 1.5 mm, fasten to det. 5 screws 19; 5 - large plate, fiberboard, fasten to the chassis 26 using angles 24 and screws 23 with nuts 25, and to bar 11 - with 3x20 screws; 6 - screw М3х15, 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 М3х6, 8 pcs .; 10 - arrow, organic glass 1.5 ... 2 mm thick, fasten to children. 7 screws 9; 11 - bar 20x20 mm, wood; 12 - driven disc, fiberglass 1 ... 5 mm thick, fasten to the holder with 13 screws 9; 13 - the holder of the driven disk, fiberglass (organic glass, polystyrene) 6 mm thick; 14 - clamps of the clutch for transferring rotation from the vernier to the KPE rotor, glass fiber laminate (organic glass, polystyrene) 6 mm thick; 15 - KPE rotor roller; 16, 17 - coupling parts, brass, bronze 0.5 mm thick, fasten to the parts with 14 screws 9; 18 - bearing 2 (differs from bearing 1 in the diameter of the holes for the fixing screws, indicated in the drawing in brackets), fiberglass with a thickness of 1 ... 5 mm, fasten to det. 20 screws 19; 19 - self-tapping screw М3х8, 8 pcs .; 20 - small plate (its contour and holes for screws to attach to the corners are shown in the drawing of the plate by 5 dashed lines), fiberboard, fasten 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 children. 3 before pressing in the pin 21; 23 - screw М3х12, 8 pcs .; 24 - furniture corner, 4 pcs., Fasten to plates 5, 20 and chassis 26 with screws 23 with nuts 25; 25 - nut М3, 10 pcs .; 26 - chassis of the receiver, fasten to the wall 1 with screws 23 with nuts 25; 27 - the cheek of the drive disc, fiberglass with a thickness of 1.5 mm, 2 pcs., Glue to children. 3 and 28 with epoxy glue; 28 - washer, fiberglass 2 mm thick, 2 pcs., Glue to children. 3 and 27 with epoxy glue; 29 - gasket, fiberglass with a thickness of 1.2 mm, glue to children. 3 and 27 with epoxy glue.
When the adjustment knob 2 rotates, the frictional torque is transferred from the driving disc to the driven 12, which is fixed with the holder 13 and screws 9 on the roller 8. Disc 12 is made of fiberglass with a thickness of 1.5 mm. The large area of \u200b\u200bthe cutout for the drive disk makes it flexible, which compensates for the possible misalignment of rollers 3 and 8 and the non-flatness of disks 27 and 12. At one end of the roller 8, using the holder 7 and screws 9, a transparent arrow of the scale 10 is fixed (it is observed through a window in the front wall radio receiver housing 1), on the other - a coupling connecting it to the KPE rotor shaft 15, consisting of two holders 14 and flat springs 16 and 17 fixed to them with screws 9. This mechanism unit is designed to compensate for the misalignment of the shaft 8 and the KPE rotor.
When manufacturing 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 2 ... 3 mm smaller than required, and only then reamed up to required 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 yourself a special drill holder, which ensures the perpendicularity of the drill axis to the plane of the workpieces. All holes in paired parts (bearings 4 and 18, plates 5 and 20) are recommended to be drilled together, connecting them during machining into one common package. A saw cut about 3 mm wide in parts 7, 13 and 14 is made with a hacksaw for metal.
The assembly of the mechanism begins with the master disk assembly. Its parts 27-29 are glued to one another and with a roller 3 with epoxy glue. Since the friction between the disks 12 and 27 required for the operation of the vernier arises from the deformation of the latter, the thickness of the spacer 29 should be chosen 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, the bearings 4, 18 and the corners 24 are screwed to the plates 5 and 20, and the holder 13 is screwed to the disk 12 (for fastening the former, self-tapping screws 19 are used, the second - screws 23 with nuts 25, the third - screws 9). After that, a roller 3 with a driving disc is threaded through a semicircular cutout in the driven disc, then through the lower (according to the figure) holes of bearings 4 and 18 and the drive disc assembly is installed on the chassis 26 so that plates 5 and 20 are at a distance of about 25 mm one from the other. Having slightly loosened the screws fastening the bearing 18 and changing within small limits its position relative to the plate 20 (the diameter of the holes for the screws 19 is quite possible to do 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. The axial play, if necessary, is selected by selecting the thickness of the washers.
Next, the edge of the cutout of the disc 12 is inserted into the gap between the discs 27 from below and through the free (upper in the figure) holes of the bearings and the hole of the holder 13 pass the roller 8. Having clamped it in the holder 13 with the screw 6, fasten the handle 2 at 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 rotating the handle 2.
The assembly is completed by installing the holder 7 on the roller 8 with the arrow 10 pre-fixed on it with screws 9 and the holder 14 with the spring 17. The second part of the coupling - the holder 14 with the spring 16 - is installed on the KPE rotor shaft 15, after which the operation of the vernier as a whole is checked.
The front wall 1 is fixed to the chassis wall 26 with screws and nuts, and to the plate 5 with screws screwed into the block 11.
Figure: 2. View of the junction of one of the options for the practical design of the vernier with the KPI
Parts materials and some technological instructions for assembling the vernier are contained in the caption under Fig. 1. A view of the junction of one of the options for the practical design of the vernier with the KPI is shown in Fig. 2.
A vernier device is understood as a mechanical drive from the tuning knob to the tuner of the radio receiver, allowing the listener to tune in to a broadcasting station. The vernier device is the main operational control of the radio receiver, therefore, it must be reliable in operation under any operating conditions. There are various designs of vernier devices: gear, worm, friction, flexible thread transmission, etc.
Their constructive difference lies in the different mechanical complexity and manufacturing accuracy, and, consequently, in the cost. Most simple
and the cheap design of the vernier device is the flexible filament deceleration mechanism, which is widely used in broadcasting receivers. The mechanical drive from the tuning knob to the variable capacitor (CVC) 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 perform with a transmission with a flexible thread, a gear transmission is additionally introduced, usually installed on the KPI unit. It should be noted that the flexible string deceleration vernier is less accurate than other gears in use. This is explained by the fact that the flexible connection does not have sufficient rigidity, therefore, during the period of operation, there may appear "backlash" and stretching of the flexible thread, which have to be compensated by the introduction of additional mechanical devices. However, although flexible-thread transmissions have significant disadvantages, they are the main vernier system of broadcasting receivers, used mainly for economic reasons. On the other hand, the choice of this transmission system is justified by purely design considerations and less stringent requirements for the accuracy of the readout (scale) devices of broadcasting receivers.
The design advantage of the flexible cord vernier device is that this mechanical system allows the radio receiver to be placed in virtually any spatial position. The scales in this transmission system can be carried out without constructive difficulties large sizes, for example, can occupy a large part of the front surface of the radio receiver housing. This circumstance is of significant importance 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 a radio listener. Accuracy
the application of indicator divisions on scale broadcasting receivers is ± 0.2 mm, which is significantly lower than in special equipment. For example, the accuracy of the location of the strokes on the scale of the special equipment radio receiver reaches 0.005 mm. In turn, the relatively low accuracy of the scale simplifies its manufacturing technology and, consequently, reduces the cost.
Let us consider the ways in which the requirements for vernier devices in flexible communication transmission systems are met. The main requirements for vernier devices are smooth tuning and zero-backlash transmission.
Smoothness of tuning refers to the amount of movement of the tuning knob (in millimeters or angular degrees) to change the tuning frequency by 1 kHz.
In broadcasting receivers, the permissible tuning error is assumed to be ± 1 kHz.
Thus, the vernier transmission of the radio receiver is calculated based on the given smoothness of tuning.
The gear ratio of the vernier device is determined depending on the class of the radio receiver. GOST 5651-64 “Broadcasting Receivers” specifies the frequencies and wavelengths that are used in broadcasting receivers (Table 2).
table 2
|
Range name |
Frequency, kHz |
Wavelength, m |
|
Long waves |
150-408 |
2000-735,3 |
|
Average |
525-1 605 |
571,4-186,9 |
|
Short |
3590-12 100 |
75,9-24,8 |
However, not all classes of broadcasting receivers apply the above ranges. For example, in class III and IV broadcasting receivers, in order to reduce the cost of their construction, it is not recommended to use the short-wave 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 a variable capacitor (CVC) 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 \u003d 258 kHz; for medium waves - V540 part of the 1080 kHz range and for short waves V4075 part of the 8.15 MHz range.
Therefore, the angle of rotation of the variable capacitor (CVC) with an absolute error of 2 kHz will be: for long waves 180 ° / 129 \u003d\u003d \u003d 1.4 °, medium waves 1807540 \u003d 0.33 ° and short waves 18074075 \u003d 0.043 °.
Considering that an average skilled tuner is able to set the angle of rotation 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 retarding vernier transmission.
It is quite natural that tuning of broadcasting receivers designed for the mass consumer is made 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 °.
The ratio of the vernier gear is determined from the ratio of the angular error on the tuning knob to the permissible angular error on the variable capacitor. 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 permissible to select 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 broadcast radio station is lengthened, which causes operational inconveniences. Usually small gear ratios are used in class III and IV radios, and large gear ratios are used in higher
class. It is not recommended to choose gear ratios less than 7.6-10.6, as the mechanical transmission ratio decreases, and the tuning according to the receiver ranges becomes inaccurate and rough.
From the above calculations, one can imagine the design of the vernier mechanism. For example, for class III and IV radio receivers, which do not have a range of short wills 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 higher, I and II classes, it is necessary to introduce an additional retarding 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 receiver determines the dimensions of the chassis, the installation of the main units, the location of the loudspeaker and the length of the scale. After agreement appearance radio receiver with design artists, who usually present sketches of the external design of the receiver, the dimensions of the scale are finally determined, and, consequently, the desired movement of the pointer arrow.
It may turn out that, according to constructive calculations, it is possible to increase the stroke of the pointer arrow, and therefore the scale of the radio receiver. For example, in the I and upper class radios, the pointer travel is up to 250 mm.
Knowing the stroke of the pointer arrow and the angle of rotation of the KPE rotor, you can determine the gear ratio of the vernier mechanism. Depending on the class of the projected radio receiver, we set the appropriate number of handle turns and, for design reasons, the diameter of the axis.
If the drum diameter d1 \u003d L / 3.14 turns out to be too large for the designed structure, it is reduced to the required size. In this case, the drum speed naturally increases.
Knowing that the rotation of the rotor of the variable capacitor is 180 °, that is, the rotor rotates by 72 turns, the gear ratio from the drum to the rotor axis will be i \u003d n1 / n2, where n 2 is the number of revolutions of the condenser rotor.
The ratio of the number of teeth of the gear and the wheel is determined as i \u003d Z2 / z1.
The number of teeth of the gear z1 that is installed on the drum is determined for technological and design considerations. Moreover, the smallest permissible number of teeth is selected for a certain Z1 and i and the gear 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 is the backlash-free transmission in mechanical systems with a flexible thread, using tension springs, rollers and split gears. The main reason for the appearance of backlash in the mechanical transmission is the occurrence of permanent deformation of the thread during the operation of the vernier device. Ego phenomenon in to a greater extent affects when used as a flexible thread of a nylon 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. 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 on the flexible thread. In fig. 27 shows various kinematic diagrams of the thread tensioning devices.
The tensioning system shown in fig. 27, bg is the most expedient from the point of view of simplicity of design, since the tension of the thread is created by one tension spring.
In 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 drum surface should be taken into account.
Thus, the systems shown in Fig. 27, whig, of which the g system is recommended for use, since in all vernier devices a drive drum is used, which in this case is used simultaneously to fasten 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 be unsuitable, therefore, when choosing a particular system, it is necessary to be guided by design considerations, determining which of the systems most closely matches the general design of the vernier device. At the same time, it is necessary to consider the simplicity of the design and therefore its cost.
In those cases when it becomes necessary to apply an additional retarding 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, which 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 can be performed without technological difficulties
by stamping or pressing. These means fulfill the basic requirements for vernier devices.
Figure: 28. Designs of split gear wheels.
In broadcasting receivers, two types of flexible-link vernier devices are used: two- and one-cable systems. Depending on the class of the radio receiver, and therefore on its cost, one or another vernier transmission system is selected. In the case where the radio receiver must receive radio transmissions via the AM and FM path, as a rule, a two-wire vernier transmission is selected. In this case, separate tuning is carried out along the amplitude modulation path and the frequency modulation path. The single-line 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.
Figure: 29. Kinematic diagram of two-cable vernier transmission.
1 - block drum K.PE; 2- AM cable; 3 - directional arrow; 4 - tension spring; 5 - vernier gears; 6 - KPE block; 7 - guide roller; 8 - VHF unit drum; 9 - cable of the FM path; 10 - tension roller; 11 - tuning axis of the AM path; 12 - tuning axis of the FM channel.
In fig. 29 shows a kinematic diagram of a two-cable vernier transmission.
As seen from Fig. 29, the two-wire vernier device consists of two flexible communication transmissions, one of which is intended for tuning along the amplitude modulation path, and the second one for the frequency modulation path. In this case, the transmission along the amplitude modulation path has a slow gear transmission from the drum to the KPE unit to increase the gear ratio. The cable tension is created
spiral spring mounted on the drum. In the vernier transmission to the VHF unit, the tension of the cable is created by a tension roller. In the depicted kinematic diagram, adjustment along the amplitude modulation and frequency modulation path is performed from two separate knobs.
There are other designs, when one is used instead of two tuning knobs, and switching to the AM and FM channels are carried out using the clutches shown in Fig. 30. The designs of these couplings are widely used in Philips broadcasting receivers. In this case, along the AM and FM paths, the switching is carried out by moving the clutch using the rocker arm to the right and left bush. Both bushings sit freely on the tuning shaft and come into rigid engagement with the shaft when the coupling is pressed against the rubber washer. The movement of the clutch is made from the rocker arm, which in turn is rotated from the levers of the main range switch. For reliable engagement of the sleeve with the movable sleeve, studs are installed on its surfaces, which, when the sleeve is pressed against the sleeve, cut into the rubber washer. Vernier cables are attached to the grooves in the bushings. In the area where the coupling is located, the tuning axis is made flat.
Figure: 30. Coupling from Philips firm.
1 - tuning axis; 2 - bushing; 3 - rubber washer; 4 - movable coupling; 5 - rocker.
In fig. 31 shows the second type of couplings. Switching the 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. Stop 5,
made in the form of a strip with a hole for the pin 7, is 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 rod 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 onto the left sleeve. Washer 3 has several cutouts for engaging with pin 7. When turning the axis, the pin 7 always falls into the cutouts of washer 3, since the moment
friction of the pin on the washer surface is much less than the torque of the tuning axis. When the rod 9 is in a free position, the right sleeve enters into mechanical engagement with the axis.
In fig. 32 shows a single cable vernier transmission system. This transmission system is very simple and is used mainly for class IV radios, which lack the short wave and VHF bands. Consequently, this vernier gear has a small gear ratio and does not require the introduction of additional deceleration on the KPI unit. The drum on which the cables are attached is installed directly on the axis of the KPI unit. Sometimes, in order to simplify the kinematic system of the vernier device, a single-cable transmission is also used in class III radio receivers, for which, according to GOST 5651-64, the VHF range is mandatory.
Figure: 31. Coupling from Philips firm.
1 - tuning axis; 2-sleeve; 3 - figured washer; 4-thrust washer; 5-limiter;
6-movable washer; 7- pin; 8 - hairpin; 9- stock; 10-spring.
Figure: 32. Kinematic diagram of a single-cable vernier transmission.
1 - KPE block drum; 2- cable;
3- directional arrow; 4-way tension spring; 5-drum unit VHF; b - tuning axis; 7 - guide roller.
The main disadvantage of a single-cable system in the case of its use 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 a rotational motion, since these blocks are mutually mechanically connected. Naturally, in this system, the movable elements of the tuners are worn out more than in the two-cable system, and, therefore, the reliability of the entire vernier device decreases. It can be seen from the given example that it is not always advisable to simplify the design in order to obtain an economic benefit, since this issue cannot be solved in isolation from other requirements imposed on a broadcasting receiver, for example, reliability.
The direction of movement of the cables in the vernier device is determined by guide rollers mounted on the soffit of the radio receiver chassis or on special brackets. Although the cost of the guide rollers is a small fraction of the total cost of a radio, the design should pay attention to the economics of their manufacturing technology. The rollers themselves are usually made of plastics.
In fig. 33, a shows the simplest method of manufacturing and fixing the roller axis; the axle itself is made by centreless grinding and pressed into an extrusion carried out in sheet material... In fig. 23b, the axis is made by turning and fastened by flaring. In fig. 23, b shows the roller axis fastening, made by mechanical compression of the metal, but the axis itself in this case is less processable to manufacture than the previous designs.
In fig. 34 shows three ways of attaching the guide rollers to the axles: using a thrust washer, selected depending on the diameter of the axis along the normal HO. 894.007 (Fig. 34, a); using a spring washer (Fig. 34, b), which does not require the production of grooves on the axis (this method is convenient for axes made by centerless grinding); by means of a hollow rivet mechanically crimped on the roller axis (Fig. 34, c).
The direction arrows of the radio are usually attached directly to the vernier cable. In fig. 35 a, b, c shows various designs of direction arrows and methods of their attachment.
When designing a vernier device, first of all, a gear system is calculated
transmission. The required gear ratio of the vernier device is determined depending on the class of the radio receiver. Then a preliminary layout is already performed, according to which the structural elements, the stroke of the pointer arrow, 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 becomes difficult, which leads to its premature wear.
Figure: 35. Designs of directional arrows.
Constructive complication of the vernier transmission due to the introduction of additional elements (for example, couplings), which increase operational convenience, is advisable only in higher-class radio receivers. In class III and IV radios, one should strive to simplify the kinematic diagram of the vernier device as much as possible.
In broadcasting receivers, the scale is graduated in kilohertz and meters. Determination of the position of the broadcasting radio station is made by the value of the wavelength. The wavelength value is graduated on a scale from left to right, in the direction of increasing.
For capacitive tuning, when the indicator arrow is at the beginning of the scale, i.e. indicates the minimum wavelength or maximum frequency, the capacitance of the variable capacitor should be minimum. The rotor plates must be removed from the capacitor stator. In VHF blocks
with inductive adjustment, when the alignment rod is made of non-magnetic material, for example brass, the position of the indicator hand at the beginning of the scale corresponds to the fully inserted alignment rod. According to these considerations, the direction of movement of the cable and, therefore, the indicator arrow is determined. In accordance with the requirements of engineering psychology, it is considered most convenient to rotate the adjustment knobs in the direction of the movement of the indicator arrow.
In properly designed vernier devices, the amount of torque at the tuning knob of the broadcast receiver does not exceed 120 Gcm.
The axles on which the drive cable is wound are manufactured 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 turns out to be insufficient, which leads to slipping of the cable on the axle during operation of the radio receiver. 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 driving axle, 1.5-2 turns are enough. A large number of turns is detrimental to 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 becomes jammed. It is also not recommended to increase the torque on the adjustment knob, since in this case the tension of the cable increases, and, consequently, its operational reliability decreases, the wear of the kinematic elements increases.
vernier system, the ease of movement of the pointer arrow is impaired.
The ease of movement of the pointer arrow is one of the advantages of the broadcast receiver. In radio receivers of the highest, I and II classes, this issue is given special attention. To facilitate the movement of the arrow, a handwheel is installed on the axis of the adjustment knob, the mass of which allows, from a slight rotational movement of the handle, to provide free accelerated translational movement of the arrow along the receiver scale. Handwheels are usually made from aluminum alloys or stamped from thick sheet steel.
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