Antenna amplifier for radio transmitter. Scheme, description

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Antenna amplifier for radio transmitter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / RF power amplifiers

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The antenna amplifier circuit does not require special explanation. The amplifier is mounted in a case made of galvanized metal 1 mm thick, dimensions - 120x60x30 mm. An aluminum plate of the same size 10 mm thick is screwed to the bottom of the case. The design of the printed circuit board is the same as in [3]. The drawing is not shown here, because board configuration is highly dependent on the type of parts used. It is only important that all connections are as short as possible and reliable thermal contact of the transistor VT1 with the heat sink plate is ensured.

(click to enlarge)

Details.

Relay K1, K2 - RES-15(002). Connectors XW1, XW2 - СР-50-73Ф. Resistors - MLT. Capacitors - KT, KM; С16.С17- KPK-MP. Inductors: LI - inductor DPMZ-3 10 μH; L2 - 14 turns on the MLT-0,5 resistor 150 Ohm PEV-2 0,35 turn to turn. L9, L11 -DPM1-0.1 56 μH. The remaining coils are frameless, wound with PEV-2 0,8 wire on a 5,5 mm mandrel. The number of turns depending on the range is given in the table. The same table shows the capacitances C3 ... C15 (pF).

Table 1
Range L3 L4 L5 16 L7 18 L1 C3 С4 С5 С7 С8 С9 С10 С11 С12 С14 С15
27..29 MHz 3 4 6 9 9 9 8 560 470 110 68 470 200 270 ... 270 270 11Q 68 27
50 Hz 2 3 5 7 7 7 6 330 270 68 39 270 120 150 ... 150 150 68 39 15

Setting up the antenna unit consists in setting up, using C16, C17, the input circuit of the antenna amplifier for the maximum sensitivity of the radio receiver. By connecting an RF generator with frequency modulation to the A5 input and switching the radio station to transmission mode, they check the output power of the PA using a power meter connected to XW2, for example, IIS-77. Capacitor C9 is selected according to the maximum output power. After making sure that there is no self-excitation of the power amplifier, a small change in the inductances L3 ... L8 (pulling and stretching the turns) achieves maximum output power. All adjustments must be made with the cable connected to the amplifier and a power cable of the appropriate length. In my version, the amplifier was powered by a separate TES-12-3-NT source, since the entire system (when used with the R-50, NRB) consumes a current of about 5,5 A in transmission mode. The power amplifier has an output power of 12 ... 15 W (50 Ohms). The sensitivity of the radio receiver from the antenna input is 0,3 μV (signal-to-noise - 12 dB).

The use of the above schemes made it possible to provide communication in the service communication ranges close to those indicated, which is 2 ... 3 times higher than the passport one. So, when installing an amplifier with a standard "quarter-wave pin" antenna on a mast 45 m high, in an area with difficult terrain, regular communication was carried out with a stationary station (with a typical antenna rise) at a distance of up to 100 km, with a car - up to 50 km. Installing the same antenna and radio station on a building 70 m high led to slightly worse results (due to power loss in the cable and the absence of an additional reception amplifier).

Literature

1. Radio station "LEN-B": Technical description. - Sofia, 1981.
2. PDS20/20 dispatcher communication console: Technical description.-Sofia, 1981.
3. Koval A. Antenna unit//Radio amateur. - 1991. - N3.-C.13.
4. Radio stations "Len-B": Technical description. - Voronezh, 1988.

Author: A. Klevtsov (RA4AED), Volgograd region, Oktyabrsky settlement; Publication: N. Bolshakov, rf.atnn.ru

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