Combined radio receiver. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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A distinctive feature of the proposed dual-band (LW and MW) receiver is that it is also designed to receive the 2nd and 3rd broadcast programs. It is assembled on a multifunctional microcircuit and one transistor, and a system of coupled circuits is used in the input circuits, which ensures high selectivity when receiving radio stations. The receiver is powered by a built-in battery or from a network unit, which allows you to use it both on a walk and at home.

On the DA1 chip (Fig. 1), a radio frequency (RF) amplifier, a detector and an audio frequency (AF) amplifier are made, and on the VT1 field-effect transistor there is a cascade that ensures matching of the relatively low input impedance of the microcircuit with the high resistance of the input circuits.

(click to enlarge)

The receiver uses a five-section mode switch (SA1) with four positions. The first two positions correspond to the reception of radio stations in the MW and LW bands, respectively. In the third position, the third wire broadcast program (120 kHz) is received, and in the fourth - the second (78 kHz).

Radio stations are received on the WA1 magnetic antenna. In the CB range, circuits operate, consisting of inductors L1, L4, tuning capacitors C2.1, C2.3 and capacitors of variable capacitance C1.1, C1.2, with which the receiver is tuned to the desired stations. Communication between the circuits is carried out through the capacitor C3. The contours of the DV range are formed by inductors L2, L5, trimmer capacitors C2.2, C2.4 and the same variable capacitors C1.1, C1.2. These circuits are connected to each other through capacitor C4.

When operating from a broadcast network, the signal is fed to the L3 coil, which is inductively connected to the L2 coil of the LW range. When listening to the third program, capacitors C5 and C7 are connected in parallel to the circuits of this range, and while listening to the second program, capacitors C6, C8, C9 (the latter to obtain the required bandwidth).

In any mode of operation, the audio frequency signal comes from the output of the microcircuit through the capacitor C20 to the dynamic head BA1. The sound volume is set by a variable resistor R6, combined with a power switch SA2. If an external power supply is connected to the receiver (through connector XS2), the GB1 battery will automatically turn off.

Most parts of the receiver can be placed on a single printed circuit board, the dimensions of which depend on the housing in which the receiver is to be mounted. For example, in fig. 2 shows a drawing of a board option in the case of using a case from the Selga receiver. By the way, the author used a dynamic head and a magnetic antenna from this receiver (with the communication coils removed and the L3 coil wound).

The magnetic antenna can be made independently using a rectangular rod measuring 125x16x4 mm from 400NN ferrite. Coils L1 and L2 are placed on paper frames at different ends of the rod: L1 contains 70 turns of PEV-2 0,25 or LESHO 16x0,07 wire, L2 - 250 turns of PEV-2 0,16. Coil L3 is placed next to L2 on the frame, it contains three turns of PEV-2 0,25 wire.

Coils L4, L5 are wound on standard frames with trimmers, for example, from the Alpinist-405 radio receiver, placing turns evenly in all sections: L4 should contain 200 turns of PEV-2 wire 0,12; L5 - 550 turns of PEV-2 0,12.

Field effect transistor - any of the KP303 series, switch SA1 - PG2 or other small-sized. Variable capacitor C1 - two-section with a maximum capacity of at least 220 pF and a block of trimmer capacitors C2 (for example, KPE-3). If there is a capacitor without such a block, you will have to install four additional tuning capacitors (C2.1-C2.4) on the receiver board with a capacitance change from 4 to 15 pF.

Oxide capacitors can be K50-6 series K52, K53, non-polar - KM, KLS, K10-17. Variable resistor R6 - series SP3-3, trimmer - SP3-19; the remaining resistors are MLT, S2-33. Connector XS2 - from a small headphone, the same can be the connector XS1. Power source GB1 - battery "Krona" or "Korund", "Nika", 7D-0,125.

An adapter plug is used to connect the receiver to the broadcast network (Fig. 3). Capacitors C1 and C2 in it must be for a rated voltage of at least 200 V.

You may wish to place the receiver in a single-program indoor loudspeaker cabinet. In this variant, it will be possible to use a dynamic loudspeaker head, but it will be necessary to slightly change the installation of the loudspeaker circuits and introduce an additional switch SA3 (Fig. 4). In the position shown in the diagram, the loudspeaker, as before, reproduces the sound of the first broadcast program. When the moving contacts of the switch are moved to another position, the broadcast network and the dynamic head of the loudspeaker will be connected to the radio circuits.

You can adjust the design using another radio receiver with MW and LW bands, which will serve as a model.

Start building from any range. The reference receiver is tuned to a low-power radio operating at the low end of the range. The scale pointer of the tuned receiver is also set to the low-frequency edge of the range, and by moving the trimmer resistor R4, characteristic noises appear in the dynamic head. Further, by moving the L1 (L2) coil along the antenna rod and the L4 (L5) coil trimmer, the best reception of the selected radio station is achieved. After that, the position of the tuning resistor engine is specified.

Then the adjustable receiver is tuned to a radio station in the high-frequency range and its high-quality reception is achieved by tuning capacitors C2.1, C2.3 (CB) or C2.2, C2.4 (DV).

It is advisable to repeat this setting several times to ensure the best result.

The next step is setting up to receive wired broadcasting programs. Capacitor C1 (see Fig. 1) is set to a position corresponding to approximately 80% of its capacity, and the receiver is connected through an adapter plug to the broadcast network. By selecting capacitors C5 and C7 (3rd program) or C6, C8 (2nd program), as well as changing the capacitance of capacitor C1 within a small range, the maximum sound volume of the selected program is achieved. In addition, you may have to pick up the capacitor C9 (for the 2nd program). The optimal level of the signals of both programs is set by a trimming resistor in the adapter plug.

Author: I. Nechaev, Kursk

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