Encyclopedia of radio electronics and electrical engineering / radio reception
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Reflex radio receivers are called, in the circuit of which some cascades simultaneously perform high-frequency and low-frequency functions. This radio receiver is designed to receive the signal of any one radio station operating in the medium wave band.
The circuit diagram of the receiver is shown in the figure.
The input oscillatory circuit LI, C1 is tuned to resonance with the frequency of the received signal by selecting the capacitance of the capacitor C1. The lower output of the coupling coil L2 is grounded at high frequency by capacitors C2 and C3. From the upper output, the signal goes to the base of the transistor VT1, used in the amplifying stage with an aperiodic load - resistor R2. Resistor R3 provides DC transistor mode. The amplified signal from the VT1 collector is fed directly to the base of the VT2 transistor, on which a resonant amplifier is assembled with an oscillatory circuit L3, C5 in the collector circuit, also tuned to the signal frequency by selecting the capacitor capacitance. From the coupling coil L4, the radio frequency signal is fed to the detector diode VD1, from the load of which R3, the detected signal through the capacitor C2 is fed back to the base of the transistor VT1. Capacitor C3 diverts the high frequency component of the detected signal to ground.
For a low-frequency signal, the cascade on the transistor VT1 is an amplifier of the audio signal, which is again fed from the collector to the base of the transistor VT2, which is connected according to the common collector circuit, since the L3 coil for low frequency is a short circuit. The BF1 phone is included in the emitter circuit.
The coil of the magnetic antenna L1 is wound with a PEV-1 wire with a diameter of 0,1 mm and contains 75 turns. The communication coil L2 of 6 turns of the same wire is wound over the winding LL. The magnetic antenna rod is made of 600НН grade ferrite with a diameter of 8 and a length of 60 mm. Coils L3 and L4 are wound on a ferrite ring of the same brand with an outer diameter of 7 mm. L3 contains 75, and L4 - 60 turns of PEV-1 wire with a diameter of 0,1 mm. As BF1, a small-sized telephone of the TM-2M type is used.
The receiver is powered by a single 316 galvanic cell with a voltage of 1,5 V and a current consumption of 1,5 mA. Such a small current is enough for continuous operation of the receiver for 200 hours.
Author: Martirosyan O.
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