Stable transistor generator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Generators, heterodynes
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The described master oscillator is designed to generate oscillations in the 10-meter amateur band. Frequency stability in the range of 28,0-29,7 MHz changes very little (deteriorating with decreasing frequency).
It is generally accepted that the most stable quartz-free self-oscillators are tube ones. However, with an appropriate calculation of the self-oscillator circuit and full consideration of the specifics of the operation of the transistor in self-generation modes at RF, the stability of the circuit can be obtained, which differs little from circuits on lamps.
The circuit used by the author (see figure) is a self-oscillator with capacitive coupling, which is the most rational in terms of design.
The most important part of the generator is the loop coil L1. It is made by hot winding on a ceramic frame with a diameter of 20 mm and is enclosed in a thin copper screen (aluminum can be used). Wire - silver plated, diameter - 0,64 mm, winding pitch - 1,5 mm, number of turns - 10,5. The coil has a quality factor of 300. This allows you to reduce the connection of the transistor with the circuit, which leads to a decrease in the influence of the parameters of the oscillatory circuit on the slope of the transistor characteristic, and this makes the stability of the generator more uniform over the range.
High-frequency chokes are wound on pre-cleaned frames of VS-1,0 resistors. Dr1 contains 130, and Dr2 - 55 turns of PELSHO 0,12 wire.
Capacitor of variable capacitance C1 type KPVM. Capacitors of constant capacity, it is desirable to use thermostable ones (made of class III RF ceramics, type A) with a tolerance of ±5%. C2 - C5 - type KT or KD stability groups M33, M47 (blue), P33, P120 (blue). C6 - C8 - type KD, you can type KVDS. Structurally, the entire master oscillator is made in the form of a hermetically sealed unit.
When setting, the resistances of resistors R1 and R2 are adjusted to establish the optimal bias voltage Ueb = 0,2 V. With the tightness of the structure, the thermal regime occurs in 20-35 minutes.
The destabilizing effect of power circuits and parasitic oscillations are practically eliminated by the correct calculation of the parameters R4, R1, and capacitors in the feedback circuit.
Power consumed from the power source - 40 mW; output power - not less than 0,6 mW.
Author: A. Yashin (UA3-160-86), Head of UW3KAK, Tula; Publication: N. Bolshakov, rf.atnn.ru
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