Antenna amplifier K_ues=38...41 dB. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Antenna amplifiers

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The proposed antenna amplifier is designed to amplify the signals of broadcasting and television stations in the meter range.

• Bandwidth, MHz, with signal attenuation at the edges of the range of 3 dB..........50...350
• Self-noise level, dB .......... 3,5
• Input impedance, Ohm..........75
• Rated load resistance. Ohm.........75
• Voltage gain with an input signal of 5 μV, dB, at a frequency of MHz: 230..........41

Schematic diagram of the antenna amplifier is shown in the figure. It is assembled on four transistors connected according to a common emitter circuit. A feature of the amplifier is the use of inductors as collector loads of transistors VT2-VT4, which reduced the blockage of the amplitude-frequency characteristic (AFC) of the amplifier at higher frequencies.

Zener diode VD1 type D814A. The amplifier remains operational when the supply voltage drops to 4 V. In this case, the gain in the entire frequency range decreases to 36 dB. To operate the amplifier at a low supply voltage, the D814A zener diode must be replaced with a KS139A or KS147A. The current drawn from the power supply will drop to 15 mA in this case.

The amplifier is mounted on four boards with dimensions of 25x40 mm made of double-sided foil fiberglass 2 mm thick. One side of the board is used as a screen. The boards are installed in rectangular recesses of the brass case and are separated from each other by shielding partitions soldered directly to the foil surface of the boards.

Coils L1, L2, L4 contain 2,5 each, and L3 - 4 turns of PEL 1,0 wire. The winding diameter of coils L1-L3 is 12, and L4 is 20 mm. Winding step - 8 mm.

The establishment of an antenna amplifier begins with the setting of the DC transistor modes in accordance with those indicated on its diagram. Then proceed to the adjustment of the frequency response. To do this, you can use the X1-19A, X1-1, or GKCH devices of any type.

The selected frequency range is set on the GKCH at the maximum swing band. A voltage of 5 μV is applied to the input of the amplifier (such a signal corresponds to an attenuation of 1 dB on the X19-50A device). Setting up the amplifier is reduced to selecting the locations of the taps from the coils L1-L4 until the required bandwidth is obtained. The frequency response can also be taken using a calibrated standard signal generator and a tube voltmeter, by shunting the latter with a 75 ohm resistor.

Authors: Yu.Bigeldin, A.Danilov, Ch.Seitnepesov; Publication: cxem.net

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