Main amplifier for STB-receiver. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Телевидение
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The kit for receiving satellite TV programs includes a parabolic antenna, which is installed in such a way that it falls into the line of sight from the satellite, a down converter and a tuner (indoor unit). They are connected to each other by a coaxial cable, the length of which usually should not exceed 15 ... 20 m, but in practice it happens even more. As a result, the signal arriving at the tuner is significantly attenuated, and the quality of the received image deteriorates.
To compensate for attenuation in the cable, I propose a main amplifier (Fig. 1). It is powered by the voltage injected into the cable and is switched on in the middle of the cable. The amplifier is assembled according to a single-stage scheme, its gain is at least 10 dB. It is built on a double-gate low-noise field-effect microwave transistor. The supply voltage is stabilized by a low-power IC DA1. LPF L1-C1, L3-C2 prevent self-excitation of the amplifier and ensure the passage of the supply voltage to the converter.
Fig.1. Schematic diagram of the main amplifier
The amplifier is assembled on a printed circuit board (Fig. 2) from foil-clad fiberglass with a thickness of 1,5 mm. All parts are SMD or conventional, with leads of minimum length (to reduce parasitic lead inductances). XW1, XW2 - connectors type "F". L4 has 2 turns of PEVTL-2 wire d0,36 mm, wound on a mandrel d2 mm, which is removed after winding.
Fig.2. Printed circuit board
The amplifier is placed in a brass or cast duralumin case. The body is sealed after adjustment. VT1 can be replaced with a domestic 3P351A-2 (amplifier parameters should improve, but such a transistor is very difficult to find). When setting up, you may have to select the resistor R3 according to the maximum gain of the device as a whole.
Author: V. Fedorov, Lipetsk; Publication: radioradar.net
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