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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Program selector for Ishim-003 radio receiver. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / radio reception Today, when you will not surprise anyone with an abundance of equipment on the supply market (including radio receivers), the efforts of amateur radio creativity are mainly aimed not at developing new products, but at introducing new service capabilities into existing equipment, which, for various reasons, at factories -manufacturers could not implement. As the practice of implementing improvements in industrial structures shows, radio amateurs sometimes find very interesting solutions. This article offers a description of one of these finds. I propose a scheme for the program selector (SVP), which was used by me when improving the radio receiver "ISHIM-003". Unlike the devices described in [1, 2], this selector can be used in radio receivers with electronic tuning, in which the varicap control voltage exceeds 15 V (the maximum allowable for the operation of CMOS devices). In addition, the SVP provides blocking of the AFC system of the radio receiver at the time of switching programs. The number of switched programs is selected depending on the possibility of receiving VHF radio stations in a particular area and can reach ten. In the SVP in question, the selection of programs is carried out by repeatedly pressing one button, while cycling through pre-set programs. A "bar" of LEDs is used to indicate the current state of the selection. The one-button method of switching programs is used because there is so little free space on the front panel of the "ISHIM-003" radio receiver to place several more switches there. In addition, it would not have done without compromising the design of the receiver. The SVP is assembled on digital microcircuits made using CMOS technology. Optoelectronic integrated circuits K249KP1 were used to decouple the varicap control circuits from the rest of the device. The selector is powered from the power supply of the radio receiver with a voltage of +15 V. The current consumption of approximately 10 mA is determined by the current consumption of the LEDs of the optocoupler and program indicators. The schematic diagram of the SVP is shown in Fig.1. The SB1 button selects the received program. At the moment the button is pressed, the +5 V voltage from its contacts through the differentiating circuit C1R1 is fed to the input of the waiting multivibrator assembled on the DD1 chip. Its purpose is to eliminate the bounce of the contacts of the SB1 button and generate an impulse to block the AFC system of the radio receiver. This pulse of negative polarity from the inverse output (pin 11) of the DD1.4 element of the waiting multivibrator goes to the gate of the field-effect transistor VT1, the drain of which is connected to the voltage circuit of the AFC of the radio receiver, and the source is connected to a common wire. When switching programs, transistor VT1 opens and closes the AFC voltage to the case. The duration of the blocking pulse of the AFC is set by the selection of elements of the integrating chain R2C2. When indicated in Fig. 1 values of the resistor and capacitor, it is approximately equal to 0,7 s. From the output of the DD1.2 element (pin 4) of the waiting multivibrator, a positive polarity pulse is fed to the counting input (pin 14) of the DD2 microcircuit.
Chip DD2 is a decimal pulse counter. It has ten outputs, on one of them there is always a high level voltage, on the other - low. At the moment the SVP is turned on, a short pulse of positive polarity, generated by the differentiating circuit C3R3, is fed to the input R (pin 15) of the DD2 microcircuit. The counter is reset, a high-level voltage appears at the output "0" of the microcircuit (pin 3), the first program is automatically turned on. With the arrival at the counting input (pin 14) of the DD2 microcircuit, a pulse from the output of the waiting multivibrator, a high-level voltage appears at the output "1" of this microcircuit (pin 2), the second program is turned on. With the arrival of the fourth pulse from the waiting multivibrator, the high-level voltage from the pin. 10 of the DD2 microcircuit through the VD1 diode enters the "R" input, the counter returns to its original state, the first program is turned on again. From the outputs of the DD2 microcircuit, the voltage is supplied to the bases of the transistors VT2 - VT5, which act as key elements. In the emitter circuit of each of these transistors, an LED of the U1 or U2 microcircuit and an indicator LED HL1, HL2, HL3 or HL4 are connected in series. When a high level voltage is applied, for example, to the base of the transistor VT2, it opens, current begins to flow through the LEDs of the optocoupler U1.1 and НL1. The indicator LED HL1 begins to emit, signaling the inclusion of the first program, and through the opened phototransistor of the optocoupler U1.1, the +22 V voltage from the power source of the radio receiver is supplied to the tuning resistor R4. From its engine, the voltage through the VD2 diode is supplied to the varicaps for tuning the radio receiver circuits. The initial programming of the SVP is performed by tuning resistors R4 - R7. Diodes VD2 - VD5 serve to eliminate the mutual influence of the resistances of the trimmer resistors R4 - R7 on each other. In our case, the SVP is designed to switch four programs. But if necessary, their number can be increased to ten. To do this, the anode of the VD1 diode is connected to the output of the DD2 microcircuit with a number corresponding to the new number of programs, and with ten programs, the diode should be excluded from the circuit. On the zener diode VD6, resistor R9 and capacitor C4, a parametric voltage regulator is assembled that feeds the SVP device. Additional stabilization of the supply voltage is necessary to stabilize the current flowing through the LEDs of the U1, U2 microcircuits and, ultimately, to eliminate the “floating” of tuning to the radio station. The SVP is connected to the radio receiver in accordance with the circuit diagram shown in fig. 2. On it, near each external output of the SVP, the point of its connection to the circuits of the radio receiver "ISHIM-003" is indicated. To turn on the "regular" tuning mode, the button S3 ("SP" - middle band) of the radio receiver is used. It is used to return buttons with latching "UP" (narrow band) and "MP" (local reception), so its contacts are not involved in the design of the receiver. The wiring diagram for the contacts of this button is shown in fig. 2. It should be noted that bandwidth switching in this receiver design is provided only for the LW, MW and HF bands, and the "UP", "SP" and "MP" buttons are not used on VHF.
The SVP device is mounted on a board made of one-sided foil fiberglass with a thickness of 1,5 mm. The size of the board depends on the number of switched programs. In a specific version for four programs, a 70x80 mm board was used. Optoelectronic microcircuits U1, U2, having a planar pin arrangement, are installed on the circuit board from the side of the printed conductors. When assembling the device, fixed resistors C2 - 23, tuned resistors SDR - 36 (R4 - R7), capacitors C1, C3 type KM - 5, capacitor C4 oxide type K50 - 16V, capacitor C2 - tantalum or any other. Diodes VD1 - VD5 any silicon small-sized, transistors VT3 - VT5 type KT315 with any letter index. LEDs HL1 - HL4 can be used any suitable in color and dimensions. The SB1 switch is small-sized without fixing, with one group of contacts for switching. In this particular version of the device, you can use a button made on the basis of the MPZ-1 microswitch. It is most convenient to place the SVP device in the radio receiver housing in the gap between the chassis and the bottom of the housing. In this case, the device board is attached with four screws to the bottom from the front panel of the receiver. Under the handles of the tuned resistors, a rectangular cutout should be made. The LEDs are placed on the front panel of the radio above the corresponding knobs of the tuned resistors. The SB1 button is located on the front panel instead of the dismantled socket for connecting the head microphone (practically not used). A view of the front panel of the radio receiver is shown in fig. 3.
A properly assembled device starts working immediately after power is applied. Perhaps, in the event of a “jump” through one program, when you press the SB1 button once, you will have to turn on a capacitor with a capacity of about 4 pF between pins 7 and 1 of the DD1000 chip. A further improvement of the proposed version of the SVP can be the use in it of the digital part of the device, the description of which is proposed in [3]. Literature
Author: N. Gorbushin, Barnaul
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