Low noise antenna amplifier. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / radio reception
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The scheme of the antenna amplifier based on stripline resonators operating in the range of 70 cm (430 MHz) is shown in fig. one.
The low noise level of the amplifier is due to the use of a low-noise microwave transistor. The amplifier has a gain of about 15 dB, has good linearity and low crosstalk. The input and output resonant circuits are segments of a strip line with taps to match the input and output impedance (75 ohms), The resonators are tuned with capacitors C2 and C4.
Ris.1
The device of the amplifier, its dimensions and dimensions of the main elements are shown in fig. 2. The body of the amplifier and both lines are made of foil fiberglass 1 mm thick. The body parts are placed with foil inside and connected by soldering. The partition (Fig. 2b) is cut out of copper (or brass) sheet 0,5 mm thick. It is necessary that all seams are carefully soldered along the entire length. The lines are soldered with foil outward between the end wall of the case and capacitors C2 and C4.
Ris.2
Trimmer capacitors C2 and C4 - piston type. Capacitors C5 and C6 are feed-through capacitors (capacitance up to 1000 pF), C1 and C3 are miniature disk capacitors with greatly shortened leads. Chokes are wound with enameled wire with a diameter of 0.3 mm. Throttle Dr1 - frameless. consists of 10 turns, Dr2 is wound on a resistor with a resistance of 1 kOhm, a power of 0,25 W and contains 12 turns. Details not shown in fig. 2. Mounted on the outside of the case. The power input (+12 V) is made in the form of a ceramic stand.
The amplifier is first tuned with capacitor C4. then C2, then with resistor R5 and again with capacitors until maximum gain is obtained. The variable resistor R5 slider must be in the middle position before setting.
Literature
- "Radio REF" (France), 1975, No. 11
Note. The closest analogue of the BFR91 (BFR90) transistor in terms of parameters and case type is the 2T367A transistor. however, it has a higher noise figure.
Publication: cxem.net
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