Power amplifier CB. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / RF power amplifiers
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Firm "CTE International SRL" serially produces RF amplifier model 737, designed to operate in the CB range. I developed a printed circuit board for domestic radio elements, built and tested the circuit of this power amplifier.
The circuit with our analogues is efficient and showed very good results despite the ease of manufacture. The amplifier turned out to be broadband, capturing all amateur radio bands from 160 m to 10 m inclusive.
Schematic diagram of the amplifier is shown in Fig.1. Figures 2 and 3 show the printed circuit board and the location of parts on the board. For the manufacture of transformer T1, six rings with a magnetic permeability of 600 NN (up to 1000 NN - non-critical) of size 7 x 4 x 2 were used, three rings were glued together with BF2 glue, and then the resulting ferrite "tubes" were folded side by side and also filled with glue. Thus, threading three turns of the primary winding and the secondary into these tubes, we obtain a transformer T1 (Fig. 4).
For the manufacture of the T2 transformer, the same rings are needed - 20 pcs, brass or copper tubes - 2 pcs. 22 mm long each and 4 mm outer diameter. I used a tube from an old telescopic antenna. I will not dwell in detail, I will refer to [I], where there is a technique for building a broadband transformer with a short-circuited turn, I give only a sketch of the location of the terminals of the transformer T2 (Fig. 5).
Coil L1 is made on a cylindrical frame with a diameter of 8 mm and a length of 10 mm. The winding consists of 19 turns of PEL-0,16 mm. Winding - turn to turn. A correctly assembled amplifier circuit works immediately, the no-load current of the amplifier depends on the transistors used and is set by R3. The amplifier operates from a source of +12 V, but remains operational at +40 V. I used domestic KP901 transistors, the quiescent current is 200 mA. Increasing the quiescent current leads to out-of-band emissions. When the supply voltage is increased to +40 V, the amplifier retains all its characteristics and works stably, no self-excitation was noticed. 0,5 W was fed to the input of the amplifier on all ranges, while the output power fluctuated: on the low bands - 6 W, starting from the 20-meter band, the power increased to 7 W, on average - 13 times relative to the input power.
The test was made on a 75-ohm load, and then with an antenna fed by a 75-ohm cable. In this amplifier, you can try more modern transistors, say KP913A, in which 8 = 1.0 ... 2,5 A / V - this is an order of magnitude higher than that of KP901A. I think the results will be good. If you have any questions or comments, please send them to the author.
Literature
- Radio. 1988, No. 12. - P.21.
Author: Yu.Ivanov, Cheboksary; Publication: N. Bolshakov, rf.atnn.ru
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