Portable transistor radio station for 144...146 MHz (retro). Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Portable transistor radio station for 144...146 MHz (retro). Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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Schematic diagram of the radio station is shown in fig. 1. It is made on four transistors.

The transmitter is assembled according to the scheme with extraneous excitation. Oscillations at fixed frequencies in the range of 72-73 MHz, generated by an exciter assembled on a transistor T3 (OS 614), are modulated in frequency by applying an alternating voltage from the carbon microphone capsule of the Central Bank to the base circuit of the transistor T3. This voltage changes the dynamic capacitances of the transistor, which ultimately makes it possible to obtain very good frequency modulation with a frequency deviation of up to 0,5 MHz at a low supply voltage.

(click to enlarge)

Transistor T4 (AF 114) acts as a doubler and power amplifier. In order to obtain maximum output power at the allowable collector current of transistor T4, the bias voltage applied to its base can be adjusted using potentiometer R12. Since transistor T3 generates in a region close to its upper cutoff frequency, a limited voltage is applied to the emitter of transistor T4. Despite this, the output power of the transmitter in the range of 144-146 MHz reaches 1-2 mW.

The receiver is assembled on transistors T1 (AF 114) and T2 (OS 604) and is a super-regenerator, the auxiliary frequency of which is selected within 100-150 kHz. A tuned capacitor is used as a variable capacitor of the oscillatory circuit (C1).

All coils of the radio station are frameless and are wound on a mandrel with a diameter of 6 mm with a wire 1 mm thick. Coil L1 contains 6 turns. L2 and L3-3,5 turns, L.4- 2,5 turns, L5-3 turns and L6- 2 turns. Choke Dr1 is wound on a ferrite core with a diameter of 1,5-3 mm and contains 20-30 turns of PEL wire 0,3-0,5 mm.

Transistors of the radio station can be replaced by the following domestic ones: OS614 with P403 or P403A, AF 114 with P411 or P411A, OS 604 with P15 or P16.

Literature

Radio No. 2, 1963
"Das Elektron", No. 14/15, 1962

Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Civil radio communications.

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