Simple dual-band receiver of direct amplification on a hybrid chip К237ХА2 can collect even a novice hobbyist. Moreover, the sensitivity and selectivity it even higher than the equivalent discrete components. And to make it easy.
Radio signals, adopted by the pin (Ан1) or magnetic (Ан2) antenna (Fig. 1) and selected L1L2C2 oscillating circuit with coil L3 when delivered via the capacitor C3 to the input 1 of the chip MC1 К237ХА2. Together with external elements R1, R2, and C4 — C7 it forms a four-stage amplifier high-frequency amplitude detector and tract enhanced automatic sensitivity adjustment.
High electrical parameters of the chips provide a loud undistorted sound receiver via a single-stage ULF transistor T1. Small-sized dynamic head Гр1 included in the circuit of its collector through a transformer TR1.
Magnetic antenna is wound on the rod 10 mm dia and 200 mm long ferrite with permeability of 400 stamps. Coils L1 and L2 contain 60 turns of wire LASO 10X0,07, L3—10 turns of PEV 0,2. They are wound on the moving paper liners.
Variable capacitor C2 with a solid dielectric. B1, B2 — toggle switch TV2-1. The power source B1 — battery 3336L.
Output transformer and speaker from any transistor radio, for example, VEF-12.
Constructive design of a receiver depends on the case. Version of the installation shown in the figure above.
If you have speakers with high impedance voice coil, for example, 0.5 GD-14, GD 0,1-9, you can collect economical transformerless ULF (Fig. 2) transistors of different conductivity. The coefficients of the transfer current of these transistors must be close.
Fig. 1. Schematic diagram of the radio.
Fig. 2. Diagram of the transformerless ULF.
Approximate values of currents and voltages in the circuits of the receiver shown in the diagrams (see Fig. 1, 2). The optimum resistance of the resistor R1 provided on the housing of the chip. The value of R3 is chosen by the maximum volume of undistorted sound.
In conclusion, Ан1 disconnect the antenna and moving the sleeve with the coil L3 when the rod antenna Ан2, find a position where a receiver has good selectivity on both bands.