Push-pull terminal amplifier of the transmitter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / RF power amplifiers
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The figure shows a circuit diagram of an economical power amplifier for a 144 MHz amateur transmitter. The amplifier is assembled according to a push-pull circuit and operates in mode B, but does not contain, as usual, at the input and output of transformers with a tap from the middle of the winding.
This is explained by the fact that the amplifier is assembled on complementary transistors, like the end nodes of low-frequency amplifiers. There is no initial bias at the bases of transistors V1 and V2 (the bases are connected to the emitters via DC chokes L3 and L4.
Inductors L1 and L2, together with capacitors C2 and C4, form resonant circuits tuned to a frequency of 144 MHz. Capacitor C1 establishes an optimal connection with the preamplifier.
At the output of the terminal amplifier, coils L5, L6 and capacitor C7 form an output oscillatory circuit tuned to a frequency of 144 MHz. Capacitor C8 establishes the optimal connection between the amplifier and the antenna.
Coils L1 and L2 should contain 3,5 turns of silver-plated copper wire with a diameter of 1 mm. Winding diameter - 8 mm, step - 1 mm. Coils L5 and L6 - 5 turns of the same wire and are made in the same way.
When repeating the amplifier, you can use domestic transistors KT914A (V1) and KT904 (V2).
The amplitude characteristic of the amplifier with input power from 50 to 250 mW is almost linear. The output power in this case varies from 0,48 to 2,24 watts.
Literature
- Etaj de pulere. - Technology. 1982, No. 4. pag. 7
Publication: N. Bolshakov, rf.atnn.ru
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