Transistor tube AM transmitter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Civil radio communications
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Currently, portable HF and VHF radio stations are widely used. For greater efficiency, reducing weight and dimensions, transistors are widely used in them. In this case, for more or less powerful radio stations, circuits are used that use a generator radio tube in the output stage of the transmitter. The anode voltage for it usually comes from a voltage converter. These schemes are complex and not economical enough.
The proposed scheme has increased efficiency and simplicity of design. It uses a powerful modulator and a rectifier as an anode voltage source (see figure).
The modulation transformer has two step-up windings - modulation and supply. The voltage taken from the supply winding is rectified and fed through the modulation winding to the anode of the output stage operating in the anode-screen modulation mode. The modulator operates in mode B and has a high efficiency (up to 70%).
Since the anode voltage is proportional to the modulation voltage, this circuit implements controlled carrier modulation (CLC), which greatly improves efficiency.
(click to enlarge)
The master oscillator is assembled according to a circuit with a common base on the transistor T1 (range 28-29,7 MHz) and gives an excitation voltage of about 25-30 V. It should be noted that transistor T1 operates at a slightly increased collector voltage, so a special selection of workable specimens may be required.
Inductor Dr1 is wound on a resistor VS-2 with a conductive layer removed and has 250 turns of PEL 0,2 wire. Coils L1 and L2 each contain 12 turns of PEL 1,2 wire. Coil diameter 12 mm, winding length - 20 mm. The taps in the L1 coil are from 2 and 6 turns. Coil L3 has 2 turns and is located at a distance of 2 mm from the "cold" end of coil L2 /
Transformer Tr1 is wound on a W 20X20 core, windings I and II each contain 1 turns of PEL 000 winding III - 0,1 turns of PEL 200 with a tap from the middle.
Transformer Tr2 is wound on a Sh12X 12 core, winding I has 300 turns with a tap from the middle of winding II - 450 turns of PEL 0,41 wire. The transmitter is assembled on a vertical aluminum chassis 60x250 mm.
Tests have shown that the transmitter provides a satisfactory modulation quality.
Author: S. Soldatov, Saransk; Publication: N. Bolshakov, rf.atnn.ru
See other articles Section Civil radio communications.
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