144 MHz band power amplifier. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / RF power amplifiers

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The amplifier has been designed to work with most portable FM transceivers. With a transceiver output power of about 5 watts, the amplifier allows you to get about 18 watts, which is quite enough for the vast majority of real situations. Any transceivers or transmitters that provide an output power of 3 ... 6 W can work with this amplifier, and exceeding the maximum specified value is highly undesirable.

Schematic diagram of the amplifier is shown in Fig.1.

Ris.1

It is assembled on a board made of double-sided foil fiberglass (Fig. 2). The foil is left on both sides to the maximum extent, only the areas adjacent to the conductors are removed.

Ris.2

In this way, on one side of the board, 7 sections of different area are formed, to which parts are soldered. The conclusions of all parts should be as short as possible. All 5 trimmer capacitors are soldered directly to the board. It is necessary to pay special attention to the quality of these capacitors and the mounting of the transistor on the board (Fig. 3).

Ris.3

First, prepare the board by drilling a hole and processing the conductors to which the transistor leads will be soldered. Second, make sure the connection between the board and the heatsink is secure (use one large heatsink that matches the size of the PCB). For fastening, 4 bolts with bushings and washers are used. The transistor is then installed using thermally conductive paste. When installing, do not overtighten the screw that secures the transistor.

The next step is to solder the transistor leads to the corresponding pads on the printed circuit board. Both emitter leads are soldered to a common wire. Then you need to install a screen (made of metal or foil textolite) above the transistor. It is necessary to cut a groove in the screen that exactly matches the dimensions of the part of the transistor over which the screen is installed.

The amplifier tuning begins at a reduced supply voltage (8 ... 9 V) and at a reduced power level supplied to the amplifier input (1 ... 2 W). Trimmer capacitors achieve maximum output power. If unstable operation of the amplifier is noted, it may be necessary to introduce a resistor R1, shown in Fig. 2. In the correct mode of operation, the amplifier should provide a gain of 5 ... 6 dB at a supply voltage of 13,5 V.

The following parts are used in the amplifier: VT1 - 2N5591 or S3007; C1, C2 - 7...60 pF; C3, C4 - 4...40 pF; C5 - 20...250 pF; C6 - 0,02 uF (ceramic). Choke DR1 has 10 turns of wire with a diameter of 1 mm on a mandrel with a diameter of 6,5 mm. On the output of the inductor, connected to the collector of the transistor, 2 ferrite rings are put on. Coils L1 and L2 have 4 turns of wire 01,6 mm on a mandrel Ø 0 mm, the length of the coils is 6,5 mm. The resistance of the resistor R16 is from 1 to 20m. In case of unstable operation of the amplifier, a 1000 Ohm resistor is installed and its resistance is reduced, achieving a stable gain (the resistor is connected between the base of the transistor and the common wire). Choke DR100 in the power circuit. must have a small inductance and allow the flow of current corresponding to the maximum collector current.

Author: Herman Cone III (WB4DBB), Translated by S.Kushneruk (RV4AI)

Sweet poison of simple solutions

1972 and 2000... It seems that we are a little late with the topics and cases that were discussed in the American and European amateur radio press more than a quarter of a century ago. But let's not talk about backlogs. To engage in self-abasement and discuss where and how much we are lagging behind - this kind of technical masochism is not that tired, it is simply fruitless, it does not accelerate progress and does not increase enthusiasm. The relatively short period of time that ended on August 17, 1998 was marked, among other things, by the fact that the mysterious balance between exchange rates contributed to a rather noticeable increase in VHF portables purchased by radio amateurs. "Dragons", "Alinkas" and other "yaezu" appeared in the hands and pockets of the SS-Russian owners and revived one of the most favorite pastimes - amplifier building. Moreover, this fun has an international character. American colleagues said to themselves more than twenty years ago: "And what kind of American does not like working with a power amplifier!". At the same time, without forgetting the well-known approach to us - a larger number, a cheaper price.

Thirty-nine years of amateur radio has led me to - how shall I put it? - Well, let's say, I'm wary of "brilliantly simple" solutions. I think that colleagues with good experimental practice could tell a lot of interesting and useful things in this regard. I, reflecting on this article, would like to say only about the following.

The article WB4DBB, describing the VHF power amplifier, allows us to conclude that with the obvious possibilities of acquiring factory-made equipment (in the same issue of the magazine "73" amplifiers of the 2-meter range with an output power of 12 to 150 W are presented, costing from 80 to 240 dollars (attention! - 1972, now the prices are completely different - S. K.), the influence of two factors is ineradicable. Firstly, the great American idea is to make something out of nothing. In the Russian version, this has its own verbal expression .. Secondly, the construction of any design is a powerful factor of self-affirmation.The author of these lines was a witness of how respectfully 50-, 60-year-old American colleagues, owners of supertransceivers, ultraantennas and superamplifiers, treated those who assembled a CW transmitter for 3 transistors. And, dear friends, pay attention to such a feature. On the one hand, the situation that I just mentioned. On the other hand, a large number of high-class designers, a high level of developments presented in "QST", "73" , "CQ" and other publications.

When translating the article, I tried, sometimes to the detriment of the accepted style, to convey not only the content, but also the manner of the author's presentation. And you see what happens. It seems that the author addresses his article to anyone. who understood which side to hold on to the soldering iron. The very description of the sequence of building an amplifier, the functions of its elements is in good harmony with the level of circuitry. However, it is well known what "miracles" VHF technology is capable of. The simplicity of the scheme and the "simplicity" of its implementation and refinement are very different things. However, even in this, beginners are lucky and ... I forgot who else. Sometimes.

Author: S. Kushneruk (RV4AI), Volgograd; Publication: N. Bolshakov, rf.atnn.ru

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