Linear broadband power amplifier (UA4UDF). Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / RF power amplifiers

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The amplifier is designed to operate in the range of 1,8 - 30 MHz into a load with a resistance of 75 ohms and develops an output power of about 10 watts. It is very easy to set up and, as a rule, starts working immediately if the elementary rules for installing high-frequency circuits are observed. Nevertheless, to obtain high parameters, it is necessary to strive to make the mounting capacitance minimal (especially the base circuits of the output transistors).

(click to enlarge)

The amplifier has a very "soft" CW keying. It is designed to be built into multi-band amateur transceivers and has the following parameters:

The frequency response is linear in the range up to 21 MHz and has a -3 dB rolloff at 30 MHz, the maximum output power in the range of 2 - 21 MHz is 10 W, the maximum output power in the range of 21 - 30 MHz is 6 W, the level of intermodulation distortion (measured at 1,8 .10 MHz): at Pout = 43 W - -5 dB, at Pout = 52 W - -30 dB, harmonic level - no more than -34 dB (without selection of transistors, at maximum output power, with selection - about -70 dB ), third harmonic level - no more than -12 dB, current consumption from sources: 100 V: 135 - 25 mA, 80 V: 50 mA, 50 V: 400 - 75 mA (with a load resistance of XNUMX Ohm)

The circuit is powered by three voltage stabilizers - 12, 25 and 50 V. A possible stabilizer circuit for 25 and 50 V is shown in Fig. 2. It is assembled according to the standard scheme on two KR124EN12 microcircuits.

Fig.2 (click to enlarge)

The amplifier is insensitive to load resistance, which can vary over a wide range, but with a resistance of less than 70 ohms, output power must be limited to avoid thermal or current breakdown of the output transistors.

Another advantage of such an amplifier circuit is reliable and simple protection on diodes VD5 and VD6.

Setting:

Resistors R26 and R25 set the duration of the rise and fall of the telegraph message, respectively. You may also have to pick up a C22 capacitor (necessarily tantalum).
R5 is equalized by the frequency response,
R17 - quiescent current VT4,
R12 - the optimal depth of the FOS.
The quiescent current VT5 and VT6 is set by selecting diodes VD1 - VD4 and their number in parallel connection.

In the absence of the need for CW operation, elements R24 - R27, C19 - C22, VD8, VD9, VT7 and SA1 can be excluded.

The following details can be used in the diagram:

VT1 - KT368, KT399,
VT2 - KT603, KT610, KT608,
VT3 - KT606,
VT4 - KT606,
VT5 - KT904, KT922A
VT6 - KT914, (at frequencies up to 14 MHz you can KT933)
VT7 - KT3107,BC212,
VD1 - VD4 - D223 or similar,
VD5 - VD6 - KD106,
VD7 - VD9 - KD522 or similar,
T1 - the best results were obtained with ferrite cups 2000НН (without a gap!) with D=22 mm and H=13 mm, the windings are wound with two slightly twisted wires PEL or PELSHO D=0,51 mm and contain 13 - 18 turns (before filling) .

Capacitor C18 is desirable to be composed of several capacitors (eg 0,33, 0,1 uF and 2200 pF).

Publication: N. Bolshakov, rf.atnn.ru

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