Satellite TV signal splitters. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Телевидение

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Reception of satellite television programs is becoming popular and affordable, as evidenced by the increasing number of "dishes" located on the roofs and walls of houses. At the same time, amateurs often connect several subscribers to one satellite dish. How to make such connections correctly is described in this article.

To connect several subscribers to one antenna, it is necessary to use special signal splitters. The simplest of them are passive. They are popular. Their disadvantage is a decrease in the signal level for each of the subscribers. And if the length of the drop cable is significant, then the reception quality may deteriorate - noise appears in the image in the form of "snow", noise in the audio channel, and even the image disappears.

To eliminate this drawback, it is necessary to use additional amplifiers or active splitters. As you know, the operating frequency range of tuners (receivers) of satellite television is 0,75 ... 2,2 GHz, respectively, the splitters used for reception should operate in this range. Of course, such devices can be purchased from specialized trading organizations. On the other hand, many of these devices are easy to manufacture and even a not very experienced radio amateur can make them, you just need to show a desire and a little skill.

The signal splitter circuit for two lines is shown in fig. 1. It is assembled according to the hybrid coupler scheme based on a broadband transformer. Two tuners can be connected to the divider output, with one of them being the master (connected to the XS3 jack), i.e. power and control of the LNB unit (converter installed on the receiving antenna) are carried out from this tuner. A second tuner connected to the XS2 socket will only receive the signal from the converter, but will not be able to control it.

In this device, there is only one element that you have to make yourself - the T1 transformer. Its design is shown in Fig. 2. For the manufacture of a transformer, you will need two tubular ferrite magnetic cores with a length of 10 and a diameter of 2,8 mm, for example, M30VN-10, size PT 2,8x1x10. Quite suitable are magnetic circuits from normalized high-frequency chokes of the DM-1 type with an inductance of 40 ... 50 μH. Through them, as shown in the figure, two pieces of PEV-2 0,32 wire are passed, then the tubes are folded together and the beginning of one piece of wire is connected to the end of the other. All conclusions must be made of a minimum length.

It is desirable to use a small-sized metal-film resistor (R1), for example, P1-12 or high-frequency C2-10 with leads of a minimum length. It is also desirable to use a high-frequency capacitor K10-17v, in extreme cases, KM, KD with leads 1 ... 2 mm long.

A sketch of the printed circuit board of this splitter is shown in fig. 3. The board is made of double-sided foil fiberglass 1,5 mm thick, one side of it is left metallized and acts as a common wire. Since the signal power is divided, the attenuation at each of the outputs will be about 4 ... 4,5 dB, the isolation between the channels at the output will be within 12 ... 15 dB.

The board should be installed in a metal case, which can be soldered from pieces of foil fiberglass.

The input and output jacks are installed in the case in such a way that their central pins can be soldered directly to the board;

If it is necessary to provide the ability to power and control the converter from both tuners, then the splitter must be made in accordance with the diagram shown in fig. 4. Here, the converter will be powered through one of the diodes, which opens when the corresponding tuner is turned on. When the second tuner is turned on, the power will be supplied from the one with the higher voltage.

The printed circuit board for this splitter option is the same as shown in fig. 3. Additionally, you will need to make a cut in the printed conductor going to the XS3 connector to install the capacitor C2. Diodes are mounted directly on the printed tracks above the capacitors, the leads of the diodes should be of a minimum length.

Both of the given variants of splitters are classified as passive devices, their use leads to a decrease in the signal level at the outputs. In some cases, reception conditions require the use of active splitters, which not only separate the signal, but also further amplify it. A diagram of such a splitter is shown in fig. 5. Its basis is a miniature monolithic gallium arsenide integrated microcircuit of the microwave amplifier MGA-86563 manufactured by HEWLETT-PACKARD. The microcircuit is a broadband microwave amplifier with an operating frequency band from 0,5 to 6 GHz.

Main Specifications

• 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 1 dB gain compression, mW 2

The microcircuit is produced in two types of cases: SOT-143 and subminiature SOT-363. In the latter case, its cost is lower and amounts to several US dollars.

The active splitter consists of an on-chip amplifier and a hybrid splitter. Its power is supplied from one of the tuners via a drop cable. One of the diodes VD2 or VD3 opens, and the voltage through the transformer T1, chokes L4 and L1 is supplied to the converter. At the same time, this voltage is also supplied to the parametric voltage regulator on the R1VD1C4 elements, and the amplifier microcircuit is powered from it through the L3 inductor.

At the input of the microcircuit, an RF filter with a cutoff frequency of about 600 ... 700 MHz is installed, which protects it from possible voltage drops and low-frequency pickups on the cable. The splitter gain is about 15 dB.

All elements of the device are placed on a printed circuit board made of double-sided foil fiberglass. Its sketch is shown in Fig. 6. The second side is left metallized and is used as a common wire, with which some printed pads and parts are connected through holes in the board.

In the device, it is desirable to use capacitors K10-17v or similar imported ones, the resistor R1 is composed of two parallel-connected resistors R1-12, MLT or any other with a resistance of 1 kOhm and a power of 0,25 W. The windings of the chokes L1, L3, L4 are made on a mandrel with a diameter of 2,5 mm with PEV-2 wire and contain 15 turns each, L2 is wound with the same wire on a mandrel with a diameter of 2 mm and contains 1,8 turns. Transformer T1 has the design described above.

If you need a splitter for four tuners, you should use the splitter circuit shown in fig. 7.

Since in this case the signal at each of the outputs is weakened to a greater extent, the device should be made active. As an amplifier, you can use the solution according to the circuit in Fig. 5. In the absence of the necessary microcircuits, the amplifier can also be made on transistors of the KT3132A-2 type. An amplifier circuit for this purpose is given in the book by E. Red "Handbook on High-Frequency Circuitry", pp. 137 - 139, published by the Moscow publishing house "MIR" in 1990.

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