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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Once again about the introduction of the Russian frequency grid into imported CBS radio stations. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Civil radio communications In [1], recommendations were given on the refinement of imported MW radio stations for operation in the Russian frequency grid. In particular, it was proposed to lower the frequency of the reference quartz oscillator (JCG) of the frequency synthesizer (MF) by connecting an additional small capacitor in parallel with the tuning capacitor, which serves to set and adjust the frequency of the JCG (ST1). In some cases, it was proposed to use a piece of coaxial cable as an additional capacitor. Although this method is simple, it turned out to be not always acceptable in practice. Most likely, this is due to the difference in the parameters of quartz resonators used in MW radio stations of different companies. So, in some copies of radio stations ("Megadzhet-2701") it was necessary to install a capacitor with a capacity of 430 pF, while the frequency of the laser was reduced by a maximum of 4,3 ... 4,7 kHz. A further increase in the capacitance of the additional capacitor only led to the disruption of generation. Changes in the capacitance of other capacitors of the laser and the connection of an additional capacitor in parallel with the quartz resonator did not give the desired result either. Therefore, we had to use another, classical way to lower the frequency of the laser, which consists in the fact that an inductor with a tuning core is connected in series with a quartz resonator [2]. By adjusting its inductance, i.e. by rotating the core, the frequency is lowered by the desired amount, in this case by 5 kHz. Practice has shown that this method is much more reliable, especially in cases where the resonators have a significant spread of parameters. It should be noted that in this case, it may be necessary to select the number of turns (ie, the average inductance of the coil) for each specific case. At first, you can approximately try 20 ... 25 turns of PEV-2 wire with a diameter of 0,15 mm on a frame with a diameter of 5 mm. Inside the frame there should be a tuning core with a diameter of 4 mm with a magnetic permeability of about 100. It is very convenient to use a quartz oscillator coil as an additional coil. It is small-sized and has a screen, which must be connected to a common wire. The number of turns depends on the permeability of the core and can range from 2 to 8 turns. In this way, it was possible to rebuild several radio stations that could not be rebuilt using the method described in [1]. No parasitic generation of the laser when the additional inductor was turned on was not noted. In the event of its occurrence, it is recommended to connect an RC circuit in parallel with the quartz resonator, consisting of a capacitor with a capacity of several thousand picofarads and a resistor with a resistance of 1,5 to 2,7 kOhm [2]. The capacitor is necessary so that the DC microcircuit mode does not change. The scheme of alteration of the JCG of the frequency synthesizer of the radio station "ALAN-100" is shown in the figure.
Points 1, 2, 3 in the diagram mark the connection points for additional elements. In order to maintain the possibility of working in the European frequency grid, it is necessary to introduce a switch that would short-circuit the inductor L1' and thereby return the frequency of the laser to its previous value. For this purpose, it is best to use an additional relay KG, which can be used, for example, RES-15 (passport RS4.591.003). This option has less effect on the frequency stability of the synthesizer. Additional elements L2', L3', SG are installed in the power circuit of the relay. They are necessary because many relays have a strong connection between the central changeover contact and the winding. As coils L2 ', L3 ', standard DPM-0,1 chokes with inductance from 50 to 100 μH are suitable. These coils can also be made independently by winding two PELSHO (or PEV-2) wires with a diameter of 0,12 mm on a ferrite ring with a magnetic permeability from 100 to 600 with a diameter of about 7 mm. The number of turns is not critical, the winding should occupy 3/4 of the circumference of the ring. The wires do not need to be twisted. The beginning of one winding is connected to a common wire, and the other to the capacitor C1'. The ends of the windings are connected to the terminals of the KG relay winding. The ring must be fixed on the board with a drop of glue. As the SA1 switch, the "SV-RA" switch available in the radio station was used. If there is none in the radio station being converted, it is possible to use the "9-CP-19" switch. In a particular case, in the Megajet-2710 radio stations, it is convenient to place the L1' coil in the gap between the midrange chip and the side metal wall of the radio station housing. Additional relay K1 can be installed under the flat cable leading to the working channel indicator. In this case, frequency tuning when working in the European grid may not be required. To control the frequency of the JCG, you can use a connected HF receiver, for example, R-326, or another MW radio station that already has a Russian frequency grid. The setting can be done without any devices at all. To do this, at first it is produced roughly, focusing on the quality of reception of radio stations operating in the Russian grid. Then you can ask one of the colleagues who have a built-in frequency counter to check the transmission frequency of your radio station. If you need to accurately set the frequency in both grids, you must adhere to the following sequence: first, the capacitor CT1 sets the frequency in the European grid, and only then, without changing its capacitance, adjust the frequency in the Russian grid by adjusting the core of the coil L1 '. After that, it is better to fix the position of the core, for example, with a drop of paraffin. Literature
Author: V. Efremov, Essentuki, RL 3/99; Publication: N. Bolshakov, rf.atnn.ru
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