The method of restructuring the radio station R-105M. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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Before you start rebuilding, you need to prepare a repair extension cord with two RM connectors (hereinafter, reference designations are given according to the radio station schematic diagram in the description) at the input and output parts - to supply the voltages necessary for the normal functioning of the radio without an external casing.

The tuning of the radio station begins with a change in the frequency of the heterodyne master oscillator on the lamp 213. The master oscillator in the transmission mode generates a directly radiated frequency. In the receive mode, by connecting the coupling variable capacitor 209 and the capacitors 207, 208, connected by the relay contacts 211, the frequency of the master oscillator is reduced by an intermediate frequency of 793,8 kHz. Since the R-105M frequency range is in the range from 36,0 to 46,1 MHz, to lower the frequency, it is enough to install additional capacitances in parallel with the existing ones.

We change the frequency of the master oscillator-local oscillator. To do this, use a powerful soldering iron (60 W or more) to heat up and remove excess solder from the screen cover, where the coil 204 is located. By heating the edges of the cover and lifting them with a scalpel, we leave a small gap freed from solder, and so on in a circle. Having freed the edges of the cover from the solder, it is necessary to solder the wire, which is not soldered in the center, but slightly to the side. After releasing this wire, you can remove the cover.

Remembering the desoldering sequence, carefully unsolder and release coil 204 from the leads on the coil itself (upper and lower), as well as from the resistor with a capacitor. Be careful, thin leads from the conductors of the coil fit the same points - do not break them. By unscrewing the screw securing the coil, you can remove it from the screen.

Attention! Do not touch the coil winding with your hands.

Do not touch the capacitor soldered to the base of the coil. The base of the coil (attachment point) is the connection point of the constructive variable capacitor 201 and the compensating capacitor 202.

It is necessary to solder an additional capacitor (according to the electrical circuit, this is connected in parallel with capacitor 201 and consisting of two capacitors with a total capacity of about 14 pF, for example, 2 to 6,8 pF. It is advisable to install capacitors of the KD, KM or small-sized KT type (gray or blue) In the author's version, the latter were used.An example of their installation is shown in Fig. 1. According to the electrical diagram, this will be in parallel with the variable capacitor 201.

Ris.1

Install the coil in place and unsolder all the leads into place. Solder the cover in several places with a hot soldering iron, soldering the "earth" lead, previously passed through the hole in the cover.

Now you need to perform the following operations:

1. Remove the top cover from the variable capacitor unit.

2. Install a capacitor with a capacity of 145 pF between the stator and rotor plates of variable capacitors 39. Refinement and selection of this capacity will be made in the future.

3. Check the frequency (this must be done with the PTT pressed down - in the "TRANSMIT" mode).

The frequency meter is connected in parallel with the resistor 152. The range overlap is checked. It should be within 26400.. .299001200 kHz. If desired, you can repeat the operations with the local oscillator, but as a rule this is not necessary. Carefully solder the cover in place of its installation. This completes the setting of the master local oscillator.

The final step in setting up the transmitting part of the R-105M is the installation of a surface-mounted installation, in parallel with the variable capacitor 108, of a capacitance of 27 ... 30 pF. It is not necessary to select it, since the resonance in different places of the range is provided with the help of switch 106 and adjustment of the capacitor 108 at different wave impedances of the antennas.

For further adjustment it is necessary to use any RF detector head (DG). In DG, it is necessary to use a microammeter with the highest sensitivity (in the author's version - 15 μA, but 50 μA is quite acceptable). High sensitivity is necessary so that, with a minimum capacitive coupling of the probe (fractions of picofarads), the adjustable circuits are not shunted, i.e. do not introduce the probe's own capacitance and thereby do not change the resonant frequency of the circuit after measurement.

Setting up the R-105M receiver

The required frequency is set (in the MW section - 27,2 MHz, in the amateur radio - 29,3 MHz), and is controlled by a frequency meter on a resistor 152 in the "Transmission" mode. Lock the tuning knob on the front panel.

In the "Reception" mode (the tangent is depressed), unmodulated oscillations of the frequency at which your station is set (amplitude - 1 ... 1.5 V) are fed directly to the plate where the antenna is connected from the high-frequency generator.

The setting begins with the contour of the 1st UHF 128:

1. In parallel with the variable section of the capacitor 127, a capacitor with a capacity of about 38 pF is soldered.

2. The adjusting screw of capacitance 124 is set to the middle position. 3. A capacitance of about 40 pF is connected to the DG probe.

4. Touch the probe of the DG with the stator plates of the variable capacitor 127.

5. Rotate the output adjustment knob on the front panel to find the position of the greatest deviation of the DG pointer.

6. With the screw of the tuned capacitor 124 (twisting or unscrewing it), you achieve the off-scale of the DG device.

7. Reduce the capacitance of the probe by connecting small capacitances in series with it, and repeat the above operation.

If the adjusting screw of the tuning capacitor during the tuning process goes into one of the extreme positions until it stops, it is necessary to adjust the total capacitance added to the circuit to a small extent. As a result, the capacitance of the probe should be no more than 0,5 pF. When using a 50µA head, the DG probe consisted of 4 1pF capacitors connected in series.

Having achieved resonance in circuit 128, we proceed to tuning the circuit of the 2nd UHF 132. The entire tuning process takes place in the same order as with the circuit of the 1st UHF. The control point is the stator plates of the variable capacitor 134. The added capacitance in the 2nd UHF is about 39 pF.

Having achieved resonance in circuit 132, we proceed to circuit 144. The capacitance that was substituted in parallel with the variable capacitor 147 (39 pF) must be clarified by the method described above. The resonance control point is also selected on the stator plates of the variable capacitor 145. This circuit 144 must be paired with the bandpass filter setting in the 1st UHF.

After that, you can put in place and tighten the shielding cover of the variable capacitors. The RF generator signal should be disconnected from the antenna plate.

Now it is necessary, without changing the frequency of the radio station, to select the frequency of the receiver's local oscillator. It should be 793,8 kHz below the frequency set and fixed on your radio. To do this, you need to apply an elementary arithmetic operation - subtract the number 793,8 from the frequency set on your radio station. The resulting frequency will be controlled by a frequency meter on a resistor 152. For this operation, in parallel with the tuning capacitance 208, after removing the screen cover, we solder a capacitance of about 30 pF. This capacity is desirable to choose as accurately as possible. The final frequency trim will be made through the hole in the front of the radio using a 208 capacitance trim screw.

This technique makes it possible, by the simplest methods and at minimal cost, to rebuild the radio station to one of the sections where it is allowed to work with FM modulation. Unfortunately, when moving from one end of the range to another, the receive and transmit frequencies do not match. To eliminate this shortcoming and use the radio station in both parts of the range (26,950 MHz ... 27,405 MHz and 29,000 MHz ... 29,700 MHz), it is necessary to modify the exciter - local oscillator unit. Instead of capacitors 237, 236 and trimmer 210, it is necessary to substitute a capacitance equivalent to these capacitors of the order of 7 pF, while the transmission frequency should not go more than ± 3 kHz from the frequency previously obtained when laying the frequency range. We solder the additional capacitance with one output to the body, with the other - to the output coming from the coil 204.

The transition table of transmission frequencies is adjusted accordingly, if it has already been compiled earlier.

The freed capacitance of the tuning capacitor 210 is used to obtain the coincidence of the receive and transmit frequencies (Fig. 2) when moving from one end of the range to the other. On the front panel, a screw with a seal is unscrewed, which closes the hole for adjusting the capacitor 208.

Fig.2

A screw with a chain is screwed into this hole. In the vacant hole through which the rotor of the container 210 can be rotated, a toggle switch of the P1T-1-V type is installed (after all the tuning work), which will switch the tuning capacitors 208 and 210 when moving from one end of the range to another.

It is necessary to solder hard wires to the toggle switch (PEV-1 00,8 mm), put them in an insulating tube, cut them in place and solder them according to Fig. 2. Then, the frequency is adjusted according to the reception as described above, first in the high-frequency section (29 MHz), and then in the 27 MHz section, by connecting the tuning capacitor 21 with a toggle switch. In this case, it is necessary to take into account the capacitance introduced by the screen cover. When adjusting the frequency to 29 MHz, it is necessary to strive so that the desired frequency for reception is achieved with the screw of the tuning capacitor 208 unscrewed.

In conclusion, I want to say that this technique may not be entirely correct in terms of switching tuning tanks, but the task was set - to rebuild the radio station with minimal costs and, if possible, using the simplest methods, which was achieved.

Author: Yu.Mikhailov (US5WAY), Lviv; Publication: N. Bolshakov, rf.atnn.ru

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