Despite the possibility of purchasing 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 important elements The transceiver (receiver, transmitter) is the unit for tuning to the operating frequency. Currently, tuning using a variable capacitor is still widespread. But with such tuning, a relatively complex mechanical vernier device is required, providing a frequency tuning density of no more than 50-60 kHz per revolution of the tuning knob. This tuning density is most comfortable when working on air.

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

To control varicaps, special wire regulating resistors of several less common types are usually used. For example, resistors SP5-35 and SP5-40A, electrical diagram which are shown in Fig. 1, are made according to a circuit with two resistive elements. In this case, both moving 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 moving system of the “precise” 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 units, 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 tuning units that are constantly in operational operation.

Currently, varicap tuning in combination with built-in digital scales is very convenient and affordable technical solution. However, the indicated properties of multi-turn adjustment 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 obviously highly wear-resistant, leads to an obviously unacceptable frequency tuning density and, accordingly, to certain inconveniences when working on air.

In B, a double-adjustable potentiometer circuit was described, composed of a dual and a single variable resistor (Fig. 2), suitable for obtaining an adjustable voltage with both low resolution from one shaft and high resolution from the other 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 produced with different resistances of the resistive elements. 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 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 unit, 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 in that it is necessary to use a dual variable resistor, preferably with a concentric arrangement of shafts and separate control: for coarse tuning, two resistors are controlled by the outer shaft, for fine tuning - one resistor controlled by the inner shaft. Such a technical solution is not widespread and accessible enough for the average radio amateur, especially those living in the outback.

To eliminate this drawback, it is proposed to use a current summing 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 resistors R2/R1 and can be chosen practically by anyone, since with an increase in the deceleration coefficient and, accordingly, with an increase in resolution, the range of regulated voltages by the second shaft, which carries out adjustment with high resolution, decreases. Figure 3 shows the resistor values ​​that provide a deceleration factor of 1:10.

The proposed technical solution opens up the widest possibilities for choosing the desired tuning density using the second shaft, and in reality it is possible to obtain quite acceptable tuning density and the width of the tuning range. In this case, the following ratios must be observed: R1>=10RP1, R2>=10RP2. And since an obviously smaller current is taken from the RP2 motor circuit, the resistance of the potentiometer RP2 can be chosen significantly greater than the resistance of the potentiometer RP1.

The proposed circuit is also convenient in that it is not critical to the choice of variable resistor resistances. To obtain 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, varying from an infinitely large “bottom” (in the tuning node, the frequency change will be minimal) to a minimum “above” (the frequency change will be maximum). Here the deceleration coefficient is determined by the ratio of the resistance of resistor R2 to the resistance between the motor RP1 and the common wire. Thus, at each position of the RP1 engine there is a certain deceleration coefficient.

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 almost an 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 ensures ease of execution and reliability in the process long-term operation and ease of use in operational work. The design of the tuning unit was tested in a single-band transceiver for the 80 m range. 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 transmitting and receiving 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. Double adjustable potentiometer. - Radio, 1965, No. 2, p. 43
2. Resistors: reference book. 2nd ed. reworked and additional - M.: Radio and communication, 1991.
3. E. Solodovnikov. Source of DC signals. - Radio amateur, 1999, No. 10, p. 36-37.

Source of publication: w. Radiomir: HF and VHF, 2007, No. 7, p.25-27

Today I continued making parts for the vernier. I exhausted a pile of paper until 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 plex, drilled the hole and cut the M3 thread. Screwed 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 “input” it is somewhat more complicated - you need to install a spring, which will pick up 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.

The photo shows the design of the “entry” for the cable.

The next part is the flywheel assembly. I fiddled with it for a very long time. There was a flywheel from "Latvia", but its design did not suit me. I had to completely redo it. A suitable sliding 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 secure it can be seen in the photo.

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

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

The photo shows the flywheel assembly.

After that, I marked the places where the units were attached 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 this “mechanism”:

The photo shows a trial assembly of the vernier mechanism.

On the flywheel axis I attached a cable rotation unit from the Latvian VHF unit. I had to shorten it, and since it is made of very fragile silumin, I used a steel bandage to fix it on the flywheel axis. I just drilled it in silumin through hole under the bandage locking screw.

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 a slight resistance that is pleasant to the hand. The surrogate arrow moves smoothly, does not stick anywhere, the thread does not “bite” or jump off anywhere. In general, I was pleased.

Again, a “smart thought” that “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 got it” because I saw that the pulley was slightly “skewed” inward of the future scale. After shaking it lightly with my hand, I saw that the play in the axis of the variable resistor was quite large. This is on the gearbox, with its rolling bearing!
Those. This unit needs to be remade - install a “cond” axis with its own bearing, and somehow flexibly connect the variable resistor axis to it. Something like this (what was at hand).

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 fiberglass 6 mm thick, 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 put 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 an internal diameter of 7 mm, 2 pcs., put on the part. 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 adjustment knob 2, torque is transmitted due to friction from the drive disk to the driven 12, which is secured using 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 housing 1), on the other - a coupling connecting it to the shaft 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 them to the 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, the cutout edge of disk 12 is inserted into the gap between the disks 27 from below and a roller 8 is threaded 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 docking point of one of the options practical design vernier with KPI

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.

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 speed"and cable slippage. There are three types of vernier devices:

1. friction type
2. with gear drive
3. drum with cable

I was forced to get to know the latter type 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 drum groove 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 figured out with the thumb and forefinger of one hand to press the cable inserted into the groove on both sides of the opening, and with the other hand to 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.