When reconfiguring the tuner of the radio, I didn’t even notice how I removed it, but it didn’t work out just as easily - surprisingly, such a simple action turned out to be quite complicated, although it consisted of separate, completely uncomplicated ones. The essence of the vernier device is that it should slow down the rotation of the tuning mechanism. Required condition functioning - complete absence " idle move"and cable slippage. There are three types of vernier devices:
- friction type
- with gear drive
- drum with cable
WITH last type I was forced to get to know each other better, and at the same time I compiled this photo - a cheat sheet.
Installation begins by winding at least 4 - 5 turns of cable onto the rotating shaft, then it is placed on the pulleys and attached to the scale indicator.
First, one side of the cable is inserted into the upper groove of the drum, then the other. The cable must continue to be held tight, as indeed throughout the entire installation operation.
The cable is completely inserted into the groove of the drum along its entire circumference. And finally, the most inconvenient (well, simply magical) “pass” is inserting the cable into the side opening. It worked only after several attempts, when I guessed big and index fingers With one hand, press the cable inserted into the groove on both sides of the opening, and with the other hand send it there.
It is most convenient to put the spring in place using tweezers with a curved tip.
Now we send the scale pointer to the extreme right position, firmly hold the fingers to stop the movement of the cable and move the scale pointer to the right edge and do not bring it to the end of 10 - 15 millimeters. Turn the drum until the pointer moves to the extreme left position, look at the distance to the end of the scale. It should be identical to the distance on the right side. If not, then now it’s not difficult to figure out how to make these distances equal.
What is "vernier"
But what is especially noteworthy about this mechanism is its name; you may not be able to pronounce it the first time, nor, indeed, will you be able to assemble it. And its name was given by the name of the French scientist and inventor Pierre Vernier, who lived in the 17th century and who was the first to make detailed description these are devices. Author Babay iz Barnaula.
To accurately tune a radio receiver to the frequency of the received radio station, a vernier is required - a mechanism that converts rotation of the tuning knob into rotation of the tuning element (for example, the KPI rotor) through a relatively small angle. To successfully perform its functions, the vernier must have a sufficient gear ratio and virtually no backlash. The proposed friction mechanism has a gear ratio of about six and is designed to work with a homemade gearbox with air-
stuffy dielectric, described by the author in “Radio”, 2016, No. 12, p. 28, 29 (you only need to place a 6 mm thick gasket between the KPI housing and the receiver chassis). The materials for its manufacture will need sheet fiberglass with a thickness of 1; 1.2; 1.5, 2 and 6 mm (instead of 6 mm thick fiberglass, 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 elbow of a telescopic antenna), epoxy glue and standard fasteners (M3 screws and nuts, several self-tapping screws and screws), and tools - a hacksaw, files, an electric drill, a set of drills and a set of taps for cutting M3 thread.
The vernier device is shown in Fig. 1. The drive disk, consisting of two fiberglass discs 27 glued together, the same number of washers 28 and spacers 29, is glued to the roller 3, at the left (as shown in the figure) end of which the adjustment knob 2 is attached. The roller rotates in bearings 4 and 18, screwed to plates 5 and 20, which, in turn, are fixed to the receiver chassis 26. The axial movement of the roller is prevented by washers 22 placed on it and pins 21 pressed in during assembly.
Rice. 1. Friction vernier device: 1 - front wall of the receiver housing, fiberboard, fasten to the block with 11 3x20 screws, and to the chassis 26 - with 23 screws and 25 nuts; 2 - adjustment knob; 3 - drive disk roller, brass tube (telescopic antenna elbow); 4 - bearing 1, fiberglass 1.5 mm thick, attach to part. 5 screws 19; 5 - large plate, fiberboard, fasten to chassis 26 using angles 24 and screws 23 with nuts 25, and to block 11 - with 3x20 screws; 6 - M3x15 screw, 4 pcs.; 7 - arrow holder 10, fiberglass (organic glass, polystyrene) 6 mm thick; 8 - driven disk roller, brass tube with an outer diameter of 7 mm (telescopic antenna elbow); 9 - M3x6 screw, 8 pcs.; 10 - arrow, organic glass 1.5...2 mm thick, attach to part. 7 screws 9; 11 - block 20x20 mm, wood; 12 - driven disk, fiberglass 1...5 mm thick, fasten to the holder 13 with screws 9; 13 - driven disk holder, fiberglass (organic glass, polystyrene) 6 mm thick; 14 - clamps of the rotation transmission clutch 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 (differs from bearing 1 in the diameter of the holes for the mounting screws, indicated in the drawing in brackets), fiberglass 1...5 mm thick, attach to part. 20 screws 19; 19 - self-tapping screw M3x8, 8 pcs.; 20 - small plate (its contour and holes for the screws for fastening to the corners are shown in the drawing of the plate with 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 part. 3 at final assembly vernier; 22 - steel washer with internal diameter 7 mm, 2 pcs., put on child. 3 before pressing in pin 21; 23 - M3x12 screw, 8 pcs.; 24 - furniture corner, 4 pcs., fasten to plates 5, 20 and chassis 26 with screws 23 and nuts 25; 25 - M3 nut, 10 pcs.; 26 - receiver chassis, fasten to wall 1 with screws 23 and nuts 25; 27 - drive disk cheek, 1.5 mm thick fiberglass, 2 pcs., glue to part. 3and 28 epoxy glue; 28 - washer, fiberglass 2 mm thick, 2 pcs., glue to part. 3 and 27 epoxy glue; 29 - gasket, fiberglass 1.2 mm thick, glue to the part. 3 and 27 with epoxy glue.
When you rotate the adjustment knob 2, torque is transmitted due to friction from the drive disk to the driven 12, secured with the help of a holder 13 and screws 9 on the roller 8. Disk 12 is made of fiberglass 1.5 mm thick. The large area of the cutout for the drive disk makes it flexible, which compensates for the possible misalignment of the rollers 3 and 8 and the non-flatness of the disks 27 and 12. At one end of the roller 8, a transparent scale arrow 10 is fixed to one end of the roller 8 using a holder 7 and screws 9 (it is observed through the window in the front wall radio receiver body 1), on the other - a coupling connecting it to the roller 15 of the KPI rotor, consisting of two holders 14 and 9 flat springs 16 and 17 secured to them with screws. This mechanism unit is designed to compensate for the misalignment of the roller 8 and the KPI rotor.
When making vernier parts, you should Special attention pay attention 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 2...3 mm smaller than required, and only then drill out to required diameter with a 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 drill holder or make one yourself, ensuring that the drill axis is perpendicular to the plane of the workpiece. It is recommended to drill all holes in paired parts (bearings 4 and 18, plates 5 and 20) together, combining them into one common package during processing. A cut approximately 3 mm wide in parts 7, 13 and 14 is made with a hacksaw.
Assembly of the mechanism begins with the drive disk assembly. Its parts 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 spacer washer 29 should be selected so that after gluing the gap between disks 27 is 0.2...0.3 mm less than the actual thickness of disk 12 .
Next, bearings 4, 18 and angles 24 are screwed to plates 5 and 20, and holder 13 is screwed to disk 12 (for fastening the first, self-tapping screws 19 are used, for the second - screws 23 with nuts 25, for the third - screws 9). After this, roller 3 with the drive disk is threaded through a semicircular cutout in the driven disk, then through the lower (as shown in the figure) holes of bearings 4 and 18 and the drive disk assembly is installed on chassis 26 so that plates 5 and 20 are at a distance of approximately 25 mm one from the other. By slightly loosening the screws securing the bearing 18 and changing within small limits its position relative to the plate 20 (the diameter of the holes for the screws 19 allows this to be done), we achieve 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 selected by selecting the thickness of the washers.
Next, insert the edge of the cutout of the disk 12 into the gap between the disks 27 from below and insert a roller 8 through the free (upper in the figure) holes of the bearings and the hole in the holder 13. Having clamped it in the holder 13 with a screw 6, secure the handle 2 to the end of the roller 3 and check the mechanism in operation. - with him normal operation It is almost impossible to hold the roller with 8 fingers while rotating handle 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 KPI rotor, after which the operation of the vernier as a whole is checked.
The front wall 1 is attached to the chassis wall with 26 screws and nuts, and to the plate 5 - with screws screwed into the block 11.
Rice. 2. View of the junction of one of the practical design options for a vernier with a control unit
Part 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 variants of the practical design of a vernier with a control unit is shown in Fig. 2.
Dear visitors!!!
Radio receivers differ in their design and the way they tune to the frequency of the received signal. That is, tuning can be carried out either using a vernier device \to search for the required frequency\, or the frequency search can be performed using 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 /tuning knob axis/. Between the guide wheels, and there are three of them in this diagram, a nylon thread is stretched - in mesh with which there is a pulley. To make this more clear, in clear example, a photograph of this device is provided.
Radio vernier device
Due to the rotation of the pulley, the KPI plates are set in motion. In diagrams for radio receivers, there is such a name as KPE block. The KPE block is a variable capacitor with an air dielectric.
Similar capacitors are found:
with a single-section block;
two-section block;
three-section block.
two-section KPE block
three-section KPE block
Such radio components are well known to you; they are found both in outdated models \USSR radios\ and in modern models radios. In modern models, KPI blocks are more advanced, as is the design of the receivers themselves, and have small overall dimensions.
Design of an air condenser - variable capacity
Let's say, if we take as an example a two-section block \Fig. 2\, this device consists of two capacitors. Accordingly, to designate this radio component, its own graphic image is given \indicated at the top, 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 unit of variable capacitance with an air dielectric.
Capacitor designation
If in a radio circuit there is, for example, a value for KPI - C40 9...365, then the radio amateur will already be able to say that this capacitor has serial number- 40, and the variable capacitance at full rotation of the rotor ranges from 9 to 365 picofarads.
Here you should also understand that a variable capacitor with an air dielectric \KPE\ consists of a moving and a stationary part. The moving and fixed parts consist of a certain number of aluminum plates. The moving part of the plates is usually called the rotor, the stationary \fixed part is called the stator.
Two things to remember graphic symbol\Fig.3\ and do not confuse them, where it is indicated:
designation variable capacitor\with air dielectric\;
designation of the tuning capacitor,
— the required capacity of which is set by adjustment, — 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 if we are talking about personal ingenuity, then such changes are made ourselves radio amateur.
So, friends, I am directly with you entering the world of interesting and identifiable things, so to speak, I am remembering my former hobby. Follow the section, it will be even more interesting further.
Without fish, even cancer is a fish!
What will be stated below is classic version"fishless". When there are neither full-fledged antennas nor proprietary equipment for “normalizing” the existing “ropes” - and the desire to “tell” is overflowing - then read. Maybe it will be useful. If everything is fine, turn off the computer and good luck with your Dx on the air!!!
Use what is at hand and don’t look for anything else!
For homemade "manual" HF tuners, often - based on economic considerations - they use air dielectric KPE - from old broadcast radio receivers. Often without a vernier and a scale, which is not very convenient for subsequent use. I, too, once again, came across the same ones. And there was a desire to improve them.
The appearance of the capacitor, assembled and disassembled, is shown in the photo. It was previously cut through one plate and, as a result, has a total capacitance of three sections of approximately 40 - 250 pF. A pair of such capacitors is quite suitable for making a hand-held HF tuner.
For the proposed modernization, enthusiasm alone will not be enough. We need "semi-finished products". I looked for them for a long time and found them in a box with fragments of old office equipment. I think many people have such a box.... :-)
I ended up selecting three gears. The number of teeth in the gears will determine the final gear ratio - it is a gearbox after all. In the end I got it 1:3, which suited me quite well. Actually, the gears selected from the heap are:
In one gear you need to make a groove for the KPE rocker arm. The groove can be made during the final assembly process on site - this will be both simpler and more accurate. It is clear that the gears were chosen not the ones we would like, but those that were available. The existing combination gear has an 8mm hole. It was possible to use a screw of the appropriate diameter to install it, but this is too much - there is no such thing in the box. I had to find a stand of the required length and diameter. In the end, everything worked out well.
The assembly process did not take very long. It took much longer to initially think through the design and, especially, to select the original gears. The photo shows that they are covered in grease residue - I didn’t touch it. Still, they work quieter and smoother. And aesthetics - we'll take care of that later...
First, we try on the first gear in place. My shaft diameters and the holes inside the gear are the same. I tried it on and it matched well. Let's move on.
Next, you need to secure the combination gear. Since the capacitor body is cast, made of aluminum alloy, nothing additional is needed - we mark and drill into in the right place hole with a diameter of 2.5 mm and cut an M3 thread. Everything is clear from the photo.
Well, finally. Make the groove for the rocker in place, it is advisable that they fit together with little friction, then there will be no need to make a damper. Since the gear is plastic, making a groove is not a problem. An awl, a file and glasses are the maximum you need.
That's all.
An attentive reader noticed that the “main” gears are not secured to the gearbox housing in any way and can be easily removed. You can come up with a fastening option, but, firstly, this will complicate the design somewhat, and secondly, this is simply not necessary! Since this is not just a KPI “in itself,” but an element of the tuner’s design, then there, inside this tuner, there will be a limiter for the tuning flywheel axis. This limiter will be the inner surface of the front panel of the case. It is enough just to select “locally” the length of the bushing put on the flywheel axis so that it is limited on one side by the front panel, and on the other, it rests against the gear with the adjustment scale attached to it. Perhaps in some cases, instead of a bushing, a thin washer will be enough. You cannot limit the flight of design ideas.
A thin disk made of any elastic material is used as a scale, based on the capabilities of the designer. Its diameter is determined only by the dimensions of the body of the entire structure. The disk is rigidly attached to gear No. 3.
As a result of the work done, we received not only a vernier with a scale, but also combined the axes of the adjustment flywheel and the scale. The use of plastic gears is more of an advantage than a disadvantage. This is not a helicopter, nothing will rotate quickly, but now it is very easy to isolate the entire control unit from the chassis, which is necessary for a T-type tuner.
Several days have passed...
Looking at the resulting product still lying on the table, I couldn’t shake the feeling that something was missing. Or vice versa: something superfluous is present... Creative dissatisfaction. And finally I understood. The structure was dismantled using hacksaw blade Everything unnecessary was removed from the cast body and what was missing was added to it. Now the design looks like this.
The sections became not three but four. The stator sections were soldered together before being installed inside the housing. The rotary ones were fastened in place using a powerful soldering iron and also additionally connected by soldering. Everything was perfectly placed. The current collection of the rotor will be done in any place convenient for installation with a piece of flexible “stocking” soldered to the rear of the rotor - there is something to fasten to.
That's all. Can be used.
Igor MISHIN
UT3IM
A vernier device is a mechanical drive from a tuning knob to a radio receiver tuning element, allowing the radio listener to tune into a broadcast station. The vernier device is the main operational control of the radio receiver, so it must be reliable in operation under all operating conditions. Exist various designs vernier devices: gear, worm, friction, transmissions with flexible thread, etc.
Their structural difference lies in the different mechanical complexity and manufacturing accuracy, and therefore the cost. The simplest
and a low-cost vernier device design is the flexible-filament retardation mechanism, which has become widespread in broadcast receivers. The mechanical drive from the tuning knob to the variable capacitor (VCA) 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 achieve using a flexible thread transmission, a gear transmission is additionally introduced, usually installed on the gearbox unit. It should be noted that the vernier device with a flexible thread retardation mechanism 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, “backlash” and stretching of the flexible thread may appear, which have to be compensated by introducing additional mechanical devices. However, despite the fact that flexible filament transmissions have significant disadvantages, 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 design considerations and less high requirements to the accuracy of the reading (scale) devices of broadcasting receivers.
The design advantage of a vernier device with a flexible thread is that this mechanical system allows the radio scale to be placed in almost any spatial position. The scales in this transmission system can be made in large sizes without any design difficulties; for example, they can occupy a large part of the front surface of the radio receiver housing. This circumstance is of significant importance for broadcasting receivers, since on large scales it is technologically easier to apply indicator divisions, inscriptions and digital symbols. At the same time, the scale becomes more visual and convenient for radio listeners to read. Accuracy
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 placement of strokes on the scale of a radio receiver of special equipment 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 how the requirements for vernier devices in transmission systems with flexible communications are met. The main requirements for vernier devices are smooth adjustment and play-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 allowable error when tuning, it is assumed to be ± 1 kHz.
Thus, based on the given tuning smoothness, 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” specifies 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 |
|
Average |
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 short-wave range.
The calculation of the gear ratio of the vernier device is carried out in the following sequence.
Knowing that the rotation angle of the variable capacitor (VCA) is 180°, the rotation angle is determined at which the adjustment error will not exceed ± 1 kHz or the absolute error will not exceed 2 kHz. Then for long waves an 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 range and for short waves V4075 part of the 8.15 MHz range.
Consequently, the angle of rotation of the variable capacitor (VCA) 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 averagely qualified 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 the given accuracy without introducing a retarding vernier transmission.
It is quite natural that the tuning of radio broadcast 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 adjustment knob, the value of which can 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 permissible to choose large gear ratios, but 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 extended, which causes operational inconvenience. Typically, small gear ratios are used in class III and IV radios, and large gear ratios are used in higher classes.
class. It is not recommended to choose gear ratios less than 7.6-10.6, since the mechanical transmission coefficient decreases, and the adjustment to 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 slow-down 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 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 course of the index arrow.
It may turn out that, according to design calculations, it is possible to increase the stroke of the index arrow, and, consequently, the scale of the radio receiver. For example, in radios of the first and highest class, the stroke of the index arrow reaches 250 mm.
Knowing the stroke of the index arrow and the angle of rotation of the gearbox rotor, it is possible to determine the gear ratio of the vernier mechanism. Depending on the class of the radio receiver being designed, we set the appropriate number of turns of the handle and, for design 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 drum revolutions naturally increases.
Knowing that the rotor rotation of a variable capacitor is 180°, that is, the rotor rotates 72 revolutions, 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 teeth of the gear and wheel is defined as i=Z2/z1.
The number of gear teeth z1 that is installed on the drum is determined for technological and design reasons. Moreover, the smallest permissible number of teeth is selected according to a certain Z1 and i and the gear z2 is calculated. Further calculation of the gears follows the usual path using the formulas given in many reference books and technical literature.
The second requirement for vernier devices is that there is no backlash in the transmission mechanical systems with flexible thread is performed using tension springs, rollers and split gears. The main reason the appearance of backlash in a mechanical transmission is the occurrence of residual deformation of the thread during the operation of the vernier device. This phenomenon is more pronounced when using nylon cord as a flexible thread. 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. Elimination of backlash in vernier transmission in broadcast receivers is carried out by the same devices that are used to create tension in a flexible thread. In 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 tension force 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 greater than 2Рт, since the friction of the thread on the surface of the drum should be taken into account.
Thus, the systems shown in Fig. are simpler in design. 27, vig, of which the g system is recommended for use, since all vernier devices use a drive drum, which in this case It is also used for fastening the tension spring.
In some cases, due to the small size of the scale device or the small diameter of the drive drum, the vig systems may be unsuitable, therefore, when choosing one or another system, it is necessary to be guided by design considerations, determining which system 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, therefore, its cost.
In cases where it becomes necessary to use additional slow-speed gearing to the variable capacitor unit, this is done using backlash-free or “split” gears (Fig. 28). The teeth of the driven gears are shifted 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 rotational moment. The gear transmission 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. By such means, the basic requirements for vernier devices are met.
Rice. 28. Designs of split gears.
Broadcast receivers use two types of flexible-coupled vernier devices: two- and single-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 when a radio receiver must receive radio transmissions via 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-wire vernier transmission.
1 - drum of the K.PE block; 2- AM cable; 3 - index arrow; 4 - tension spring; 5 - vernier gears; 6 - KPI block; 7 - guide roller; 8 - drum of the VHF unit; 9 - cable of the FM path; 10 - tension roller; 11 - AM path adjustment axis; 12 - axis of adjustment of the FM path.
In Fig. Figure 29 shows a kinematic diagram of a two-cable vernier transmission.
As can be seen from Fig. 29, the two-cable vernier device consists of two flexible transmissions, one of which is intended for tuning along the amplitude modulation path, and the second - along the frequency modulation path. In this case, 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
spiral spring mounted on the drum. In the vernier transmission to the VHF unit, the cable tension is created by a tension roller. In the kinematic diagram shown, adjustment along the amplitude modulation and frequency modulation paths is made 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 broadcast receivers. In this case, along the AM and FM paths, switching is carried out by moving the coupling using a rocker arm to the right and left bushings. Both bushings sit freely on the tuning axis and are rigidly engaged with the axis when the coupling is pressed against the rubber washer. The clutch moves from the rocker arm, which in turn rotates from the levers of the main range switch. To ensure 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 vernier gear cables are attached to the recesses of the bushings. In the area where the coupling is located, the adjustment axis is made flat.
Rice. 30. Philips coupling.
1 - adjustment axis; 2 - bushing; 3 - rubber washer; 4 - mobile coupling; 5 - rocker arm.
In 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 securing the bushings to the tuning axis. Both bushings 2 sit freely on the axis, and their movement along the axis is limited by thrust washers 4. Stopper 5,
made in the form of a strip with a hole for a pin 7, rigidly fixed to 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 rod 9 moves to the left, bar 6 moves, and the pin engages with washer 3, pressed onto the left bushing. Washer 3 has several cutouts for engagement with pin 7. When turning the axis, pin 7 always falls into the cutouts of washer 3, since the moment
the friction of the pin on the surface of the washer is significantly less than the torque of the tuning axis. When the rod 9 is in a free position, the right bushing enters into mechanical engagement with the axis.
In Fig. Figure 32 shows a single-cable vernier transmission system. This transmission system is very simple and is used mainly for class IV radios that do not have a short wave and VHF range. Consequently, this vernier gear has a low gear ratio and does not require the introduction of additional deceleration on the gearbox unit. The drum on which the cables are attached is installed directly on the axis of the KPI unit. Sometimes 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 - adjustment axis; 2-bushing; 3 - figured washer; 4-thrust washer; 5-limiter;
6-movable washer; 7- pin; 8 - hairpin; 9- rod; 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 VHF unit; b - tuning axis; 7 - guide roller.
Main disadvantage single-cable system, when used in radio receivers that have 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 block receives rotational movement, since these blocks mutually mechanically connected. Naturally, in this system the moving elements of the tuning units wear out more than in a two-cable system, and, consequently, the reliability of the entire vernier device decreases. From the above example it is clear that it is not in all cases advisable to simplify the design in order to obtain an economic gain, since this issue cannot be solved 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 guide rollers installed 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 the radio, care should be taken when designing economic issues technologies for their production. The rollers themselves are usually made of plastic.
In Fig. 33, a shows the simplest method of manufacturing and securing the roller axis; the axle itself is made by centerless grinding and pressed into an extrusion performed in sheet material. In Fig. 23, b The axle is made by turning and fastened by flaring. In 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 to manufacture than previous designs.
In Fig. 34 shows three methods of attaching guide rollers to axles: using a thrust washer, selected depending on the normal diameter of the axle BUT. 894.007 (Fig. 34, a); using a spring washer (Fig. 34, b), which does not require making grooves on the axle (this method is convenient for axles produced by centerless grinding); using a hollow rivet, mechanically compressed on the roller axis (Fig. 34, c).
The radio indicator arrows are usually attached directly to the vernier transmission cable. In Fig. 35 a, b, c shows various designs of indicator arrows and methods of their fastening.
When designing a vernier device, first of all, the gear system is calculated
transfers. Depending on the class of the radio receiver, the required gear ratio of the vernier device is determined. Then a preliminary layout is carried out, according to which the structural elements, the stroke of the index arrow, the length of the scale, the design of the tension roller system, etc. The flexible connection made 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.
Rice. 35. Designs of index arrows.
Structural complication of the vernier transmission due to the introduction additional elements(for example, couplings), which increase operational convenience, are advisable only in radio receivers of the highest classes. In radio receivers of classes III and IV, one should strive to simplify the kinematic circuit of the vernier device as much as possible.
In broadcast receivers the scale is graduated in kilohertz and meters. The position of a broadcasting radio station is determined by the wavelength. The wavelength is graduated on the scale from left to right, in the direction of increasing.
For capacitive tuning, when the indicator needle is at the beginning of the scale, that is, indicating the minimum wavelength or maximum frequency, the capacitance of the variable capacitor must be minimal. The rotor plates must be removed from the capacitor stator. In VHF blocks
with inductive tuning, when the tuning rod is made of a non-magnetic material, for example, brass, the position of the indicator needle 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 adjustment knobs in the direction of movement of the indicator arrow.
In properly designed vernier devices, the torque on the tuning knob of a broadcast receiver does not exceed 120 G cm.
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 operation of the radio. The most convenient axles for operation have diameters of 6-10 mm.
Based on the known Mvr and R, we find that the force on the cable should not exceed 300 G. To ensure reliable mechanical connection of the cable with the drive axle, 1.5-2 turns are sufficient. Big number turns has a detrimental effect on the operation of the vernier device. This is explained by 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 another and jams the entire transmission system. 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, and the wear of the kinematic elements increases.
vernier device system, the ease of movement of the pointer deteriorates.
The ease of movement of the index arrow is one of the advantages of a broadcast receiver. In radios of the highest, I and II classes, special attention is paid to this issue. To facilitate the movement of the arrow, a handwheel is installed on the axis of the adjustment knob, the weight of which allows it to be easily rotational movement handles provide free accelerated forward movement arrows along the receiver scale. Handwheels are usually made from aluminum alloys or stamped from thick sheet steel.
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