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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Antenna amplifier. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Antenna amplifiers

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The Schottky-barrier FET amplifier proposed in [1] was tested to receive weak TV signals and showed fantastic results. So, a barely distinguishable image of the 9th channel of the Kamensk-Shakhtinsky repeater (100 km) was restored almost to normal when this amplifier was connected. For example, a two-stage amplifier based on KT3132 transistors did not give even close to such an effect.

Antenna amplifier. Antenna amplifier circuit

The circuit adapted for TV reception is shown in Fig. 1. The amplifier is resonant and is tuned from the 6th to the 12th channels by the resistor R3. The LI coil is frameless and contains 5 turns of PEV 0,7 wire on a mandrel with a diameter of 7 mm. Withdrawal - from the 1st turn from the bottom. I must say that PTSs are very sensitive to static electricity, network pickups and input overloads. Although the gate of the transistor is connected to the body through the L1 coil, even a very small charge (from a comb, for example) entering the X1 input causes it to breakdown. Therefore, it is risky to connect random antennas, especially with a split vibrator. The central core of the supply cable must be connected by direct current to the screen, and it, in turn, to the carrier mast. The printed circuit board of the amplifier is shown in Fig.2.

Antenna amplifier. Antenna amplifier printed circuit board

The amplifier can be made broadband (Fig. 3) by connecting a broadband transformer T1 with a transformation ratio of 1:9 to the input. T2 is designed to match the output impedance of the amplifier with the cable resistance, which increases the efficiency compared to the inclusion shown in Fig. 1. It is not necessary to use powerful PTSs in the amplifier as in [1], instead of them, such as ZP325 (AP325) work almost as well. Transformer T1 is wound on a K7x4x2 100 NN ring and contains 4 turns in three PEV 0,2 wires. T2 - on the same core 4 turns in two wires. In both schemes, K is a ferrite bead, dressed on the drain output to prevent self-excitation in the microwave.

Antenna amplifier. Broadband amplifier

For the experiment, you can replace the PTS with a conventional low-noise FET KP312A (with the appropriate correction of R1 and R2). The difference in performance is more than convincing.

Literature

1. S. Franklin (WВ5KGL), radio amateur. - 1992. - N3. - P.46 - 47.

Author: A. Ryzhkin; Publication: cxem.net

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