Two microwave inputs for NTV-2000 and NTV-1000 receivers. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Телевидение

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If you have equipment for receiving NTV + programs, then its capabilities can be expanded and receive programs relayed by other satellites, for example, from the HOT BIRD group (13 ° E). The present article is devoted to the solution of this problem.

To receive satellite television programs in our country, an antenna with a diameter of 0,9 m or more is used. However, few people know that in most of the European territory of Russia it is possible to receive not only NTV +, but also programs from HOT BIRD satellites. To do this, you just need to additionally install a 10,7 ... 11,7 GHz band converter (or a wider band 10,7 ... 12,7 GHz). For ease of use in this case, you need a two-input receiver. Unfortunately, in most cases, NTV+ program reception sets include NTV-2000 or NTV-1000 receivers, which have only one microwave input. It is hardly convenient to make any mechanical switches for switching two converters. It is desirable that this be done automatically when switching channels of the receiver. A description of just such a switch is given below.

The diagram of the switch, which is installed at the input of the receiver in the form of a set-top box, allows you to automatically switch two converters, is shown in fig. 1. The device contains an adder assembled on a hybrid coupler (T1 R1). The outputs of the first and second converters, respectively, are connected to its inputs through capacitors C1 and C2. The adder provides decoupling between the outputs of the converters and thereby reduces the influence of the connecting cables of the converters on each other. The output of the device is connected to the input of the receiver, and from the latter the supply voltage is supplied to the converters. However, power is supplied to only one of them, so only one will work. But which one - it depends on the position in which the contacts K1.1 of the electromagnetic relay K1 are located.

When the relay is de-energized (shown in the diagram), the voltage from the receiver through the transformer T1, inductors L2, L3 and relay contacts is supplied to the converter connected to "Input 2". If a constant voltage of more than 1,5 V is applied to the "Control" bus, the transistor VT1 will open and the relay, which receives voltage from the receiver, will work. With its contacts, it will turn off the power from the converter connected to "Input 2", and apply it to the converter connected to "Input 1".

In a device assembled according to this scheme, the relay is powered by the voltage supplied to the converters. Therefore, the relay must be economical, as it additionally loads the power supply of the converter. If such a relay cannot be purchased or the current consumed by the device itself must be reduced to a minimum, transistors should be used as keys, and the relay can be assembled according to the diagram shown in Fig. 2. Here, the power supply to the converters is also carried out through the transformer T1, one of the transistors VT1 or VT2 and the corresponding inductors L1 - L4. On these transistors, a part (0,3 ... 0,4 V) of the supply voltage drops. When the voltage on the control bus is more than 1,5 V, the transistors VT3, VT5 will open, while the transistor VT2 will also open, and the supply voltage will be supplied to the converter connected to "Input 2". When the voltage on the control bus is less than 1 V, these transistors will close, and VT4, VT1 will open, and the supply voltage will be supplied to the converter connected to "Input 1". The device itself will consume a current not exceeding 6 ... 7 mA.

The adder on the hybrid coupler provides a not very large decoupling between the reduction cables of the converters over the microwave. The best decoupling can be obtained by using special microwave switching diodes, such as KA517A. The switch diagram for this case is shown in Fig. 3. It is in many ways similar to the diagram in fig. 1, and the voltage switching is carried out by the relay. But switching diodes VD1, VD2 are included in the signal bus, which open only when they are energized from the relay. In this case, both the microwave signal and the supply voltage to the converter are fed through a diode. Part of the supply voltage (about 0,7 V) drops across the diode, but this, as a rule, does not affect the normal operation of the converter. Due to the fact that in the closed state the KA517A diode has a high resistance and low capacitance (fractions of pF), a small effect of the drop cable of an unplugged converter is provided. In the on state, this diode has a low loss resistance (1 ... 2 ohms), so the signal power loss is small.

Structurally, most of the elements of any of the device options are placed on a printed circuit board made of double-sided foil fiberglass with a thickness of 1 ... 1,5 mm. One of its sides is left metallized, while the width of the conductors through which the microwave signal is transmitted must be equal to the thickness of the board - this will ensure better matching of the device with the converter.

For a device made according to the scheme in Fig. 1, a sketch of the printed circuit board is shown in fig. 4. The outputs of the emitter of the transistor and resistor R2 are soldered to its metallized side through the holes. In addition, the area to which the output cable is soldered is connected by foil along the edge of the board to its second side.

The board is installed in a metal case. Input jacks XS1, XS2 are placed on its wall. A separate body can not be done. In this case, the side walls, which should be made from a tinned copper or brass strip about 20 mm wide (foil fiberglass is also suitable), are soldered to the board from four sides and then their joints are soldered together. Preliminarily, mounting holes for high-frequency connectors are made in one of the walls, and holes for the cable and wire for supplying the control voltage are made in the other. After debugging and checking the device, it can be closed with a removable cover or soldered. For a device assembled according to the scheme in Fig. 2, a sketch of the printed circuit board is shown in fig. 5.

If desired, the manufactured switch can be built into the receiver case, since there is enough space there. A sketch of the printed circuit board of this option and for the circuit in fig. 3 is shown in fig. 6. Here, the sockets of the microwave connector type "F" are soldered directly to the board: with the central conductor to the signal conductor, and with the body - to its reverse side. Previously, the nest housings must be carefully tinned, avoiding overheating in order to avoid damage to them.

In the device according to the diagram in Fig. 1 and fig. 3 applicable parts: transistors KT315A - KT315E, KT3102A - KT3102D and similar; diode - any small-sized rectifier. It is desirable to use a small-sized relay RES49, RES60, REC37 with a winding resistance of at least 0,8 kOhm and a response voltage of 12 V. They must first be checked for reliable operation at the selected supply voltage. A relay with a lower winding resistance and a lower response voltage is also suitable, but then a quenching resistor must be connected in series with it. True, in this case, the relay will additionally load the power supply of the converter, which is undesirable.

Resistor R1 is recommended to use high-frequency - P1-12 or C2-10, removing the leads from it and soldering directly to the printed conductors. The remaining resistors are MLT, C2-33 or any others. It is better to use unpackaged capacitors - K10-17V, in extreme cases, KM-5, KD are suitable, but their leads will have to be shortened to 1 ... 2 mm.

Transformer T1 is made as follows. Two PEV-2 0,3 wires are threaded through two ferrite tubes about 9 mm long (from DM type chokes). Then the tubes are folded together, the ends of the wires are tinned and connected in accordance with the diagram. Leads should be as short as possible. The implementation of the design of such a transformer is described in more detail in "Radio", 1996, No. 11, p. 12. The inductors are wound with PEV-2 0,2 wire on a mandrel with a diameter of 2,5 mm and contain 10-15 turns each.

In the device according to the diagram in Fig. 2, similar parts can be used, only as VT1, VT2 it is allowed to use transistors KT209I, KT209E, KT209K, KT209M, KT208B, KT208D, KT208I, KT208M.

A little about the control signal. In order for the device to switch converters automatically when switching channels of the receiver, you can use the signals that are used to control individual components of the receiver. The most suitable for this are the signals for switching the operating modes of decoding devices (decoders). Four such modes are set (programmed) from the remote control of the NTV-2000 receiver: "no" - without a decoder and three modes of the decoder - "d1", "d2", "d3". As a control signal, a signal is selected that sets the operating mode without a decoder "no". This signal can be removed from jumper J28 located next to the processor (see Figure 7). In the "no" mode, this jumper is logic low (less than 0,4 V), and in the rest - logic 1 (approximately 4,7 V).

To feed this signal to the device, any small-sized socket is installed on the back of the receiver by connecting it to jumper J28. In this case, in the "no" mode, i.e. when the decoder is turned off, the supply voltage is supplied to the converter connected to "Input 2". Therefore, a converter designed to receive signals from the HOT BIRD satellite is connected to this input. In the decoder mode, jumper J28 will have a voltage that will open transistor VT1, turn on relay K1 and apply voltage to the converter connected to "Input 1". It is to this input that the NTV + converter should be connected. For the scheme in fig. 2 converters must be connected in reverse. Since the operating modes of the decoders can be programmed from the control panel for each channel separately, this is equivalent to programming the connection of one or another converter, i.e. their switching will be performed automatically, in accordance with the channel number.

To install a switch assembled on the board shown in fig. 6, it is necessary to remove the rear wall of the receiver, for which two screws and a nut securing the input microwave socket are unscrewed. Holes are drilled in the panel for nests and fixed to it with nuts. Then the panel with the board is put in place - this way the board will stay on the slots. It is connected with conductors to the receiver board, and the power to the relay is taken from the +12 V power bus (the terminal of the U302 voltage regulator microcircuit closest to the rear wall). The "Exit" socket is connected with a jumper to the receiver's input (Fig. 8). So it turns into a two-way.

If the receiver is planned to be used without a decoder, then when switching the decoder operating modes, the image and sound at the RF output and the "TV" card may disappear in some cases. To prevent this from happening, pins 1 and 2, 5 and 6, 19 and 20 are connected with jumpers on the "DECODER" scart.

In addition, to manage the switch, i.e. switching converters use the signal "DEV" (two-stage change in image brightness), but then at the same time as switching converters, the brightness will automatically switch. If this suits, the signal to the switch is removed from jumper J36, which is located next to the tuner (microwave unit) of the receiver.

Author: I. Nechaev, Kursk

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