Broadband aperiodic RF amplifier. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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The high-frequency amplifier brought to the attention of readers can find the widest application. This is an antenna amplifier for a radio receiver, and an amplifying attachment for an oscilloscope with a low sensitivity of the vertical deviation channel, and an aperiodic IF amplifier, and a measuring amplifier.
The input and output of the amplifier are designed for inclusion in a line with a characteristic impedance of 75 ohms. The operating frequency band of the amplifier is 35 kHz - 150 MHz with unevenness at the edges of the range of 3 dB. The maximum undistorted output voltage is 1 V, the gain (with a load of 75 ohms) is 43 dB, the noise figure at a frequency of 100 MHz is -4,7 dB. The amplifier is powered by a 12,6 V source, the current consumption is 40 mA.
Schematic diagram of the amplifier is shown in the figure. It consists of two amplifying cells connected in series, in each of which the resistive amplifying stages on transistors N1, T3 are loaded on emitter followers on transistors T2, T4. To expand the dynamic range, the current through the last emitter follower was chosen to be about 20 mA. The amplitude and frequency characteristics of the amplifier are formed by the elements of the frequency-dependent feedback circuit R4C2, R10C5 and the chokes of a simple high-frequency correction Dr1 and Dr2.
Structurally, the amplifier is made on a printed circuit board made of foil fiberglass and placed in a silver-plated brass case.
The connectors are high-frequency connectors SR-75-166 F. High-frequency chokes Dr1 and Dr2 are frameless. Their windings contain 10 turns of wire PEV-1 0,25, the diameter of the windings is 5 mm.
If the gain of 43 dB is excessive, only one amplifying cell can be used, and depending on the intended purpose, either on transistors T1, T2 with a supply voltage of + 5 V, or on transistors T3, T4 with a supply voltage of + 12,6 V. In the first In this case, the noise figure is lower, but the maximum output voltage is also lower (about 400 mV); in the second case, the noise factor is somewhat higher, but the maximum voltage at a load of 75 ohms is 1 V. The gain of both amplifying cells is approximately the same (21-22 dB) over the entire range of the indicated operating frequencies, and when using one cell, the frequency band is even wider (from 30 kHz to 170 MHz with 3 dB edge banding).
In conclusion, it should be noted that when assembling the amplifier, strict observance of the requirements for installation in the decimeter range is mandatory.
Author: N. Dontsov, Kharkov; Publication: N. Bolshakov, rf.atnn.ru
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