Power amplifier at 27 MHz. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Power amplifier at 27 MHz. 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 amplifier has an output power of about 8 watts with an input power of 0,5 watts.

Fig.1 (click to enlarge)

Installation is carried out mainly on the "patch" of fiberglass, glued to the bottom of the case (Fig. 2). Other mounting options have not been tested. I think a PCB mount is fine. The conclusions of the parts connected to a common wire are soldered directly to the foil. Reed relays K1, K2 are soldered to the foil with the leads up. The VT3 transistor is installed with the body down, while an aluminum radiator is screwed on top of the threaded part (after mounting the radio components).

Power amplifier at 27 MHz. Mounting
Ris.2

The simplex radio communication mode facilitates the thermal regime of the transistor, so the requirements for the size of the cooling surface of the radiator are somewhat reduced. The shortened leads of the base and collector are soldered to the "patch", and the conclusions of the emitter after a slight bend to the foil.

Chokes Dr1, Dr2 and coil L2 are installed vertically. Relay Kl, K2 - RES-55A RS4569607, capacitor C1 - KD-1, other capacitors KM-4, KM-5. Dr1, Dr2 DM-0,1 20..50 μH. Power connector for portable radios. Coil L1 is made of silver-plated wire, PEV-2 wire is used for L3, L4, L2. The winding data of the coils are shown in the table.

Power amplifier at 27 MHz. Table

Before adjustment, an active load of 50 ohms with a power of at least 8 watts is connected to the output of the amplifier. The output connector of the radio station is connected to the input of the amplifier through a piece of 50-ohm cable about one meter long, which will later be used during operation. A reduced supply voltage is applied to the circuit, at which the relays still reliably operate. During operation of the transmitter, by stretching and compressing the turns of the coils L1, L3, L4, they achieve the maximum signal level at the load. If necessary, adjust the capacitances of the corresponding loop capacitors. In some cases, you can try to more accurately select the connection points for the L1 coil taps. Self-excitation is possible if the circuits are incorrectly configured and the load mismatch is significant.

It is of interest to use this amplifier in a camping version, for example, from a fishing or hunting place, when the antenna (for example, a wire GP with counterweights) is fixed on a tree or other high object, and the amplifier is powered by a car battery or other autonomous source that provides a current of at least 1 A .

The author uses this amplifier in conjunction with a quarter-wave GP installed on the roof of a 5-story building. The range of local communications reached 50 km, while the maximum range was not tested. During the hours of ionospheric passage, contacts were made with stations in the North Caucasus, Ukraine, and the Urals with a range of more than 1500 km.

When installing a transmitting antenna near television antennas, it is imperative to turn on the low-pass filter at the output of the amplifier.

Literature

Radio amateur №9 1996

Publication: N. Bolshakov, rf.atnn.ru

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