UHF antenna amplifier on a microcircuit. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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UHF antenna amplifier on a microcircuit. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Television antennas

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The antenna amplifier of the decimeter range (21st - 69th television channels) proposed for repetition by radio amateurs is very small due to the use of a miniature microcircuit. In this, it differs significantly from those considered earlier on the pages of the magazine.

With the development of television broadcasting in the UHF, the interest of radio amateurs in antennas and antenna amplifiers of this range is growing, and the availability of a variety of element base for sale allows developing very tiny antenna amplifiers. As a rule, they are performed on low-noise bipolar, less often on field-effect transistors. At present, integrated circuits have also become available, on which subminiature low-noise UHF antenna amplifiers can be assembled.

An example is the MGA86563 monolithic gallium arsenide integrated circuit manufactured by HEWLETT-PACKARD. It is a broadband microwave amplifier with an operating frequency band from 0,5 to 6 GHz.

The main parameters of the microcircuit

Gain (at a frequency of 2,4 GHz), dB......21,8
Noise figure (at a frequency of 2,4 GHz), dB......1,6
Supply voltage, V ...... 5
Current consumption, mA......14

Output power with gain compression by 1 dB, mW (more than 0,3 V at a load of 50 ohms) 2

They produce a microcircuit in two cases: SOT-143 and subminiature SOT-363. The cost of a microcircuit in a subminiature package is lower and equals to several dollars. True, in this design it is difficult to obtain a uniform gain over the entire operating frequency range of the microcircuit (up to 6 GHz), but this is not required for the UHF antenna amplifier (up to 900 MHz).

A feature of the microcircuit is the supply voltage to it through the output terminal. This allows it to be used in an antenna amplifier with supply voltage through the output cable without any special circuit solutions.

To build a low-noise antenna amplifier on such a microcircuit, in the general case, a minimum of details is required. However, this approach, according to the author, cannot be considered correct. The fact is that, like all microcircuits in the microwave range, MGA86563 is very sensitive to static electricity charges, input overloads and excess supply voltage. This is typical for antenna amplifiers, so it is necessary to take measures to protect the microcircuit from harmful factors. In this case, of course, the amplifier will become a little more complicated, but the reliability of its operation will increase.

Schematic diagram of the amplifier proposed by the author is shown in fig. 1. Diodes VD1, VD2 are installed at its input, which protect the microcircuit from electrical discharges and powerful radio signals. The C2L1C3 high-pass filter with a cutoff frequency of about 450 MHz suppresses signals with lower frequencies and thereby also protects the microcircuit from powerful low-frequency signals. The output of the microcircuit is connected directly to the output of the amplifier and the drop cable (contacts X3, X4). To protect the output circuit from overvoltage or from negative polarity voltage at the output, capacitor C2 and zener diode VD4 are connected through inductor L3. These small complications of the amplifier made it possible to largely protect the microcircuit from the effects of harmful factors.