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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING STB converter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Телевидение Three decades ago, many radio amateurs were interested in ultra-long-range television reception. How much work, skill and invention they showed, improving television receivers and creating complex antenna systems that made it possible to "bypass" the vagaries of radio wave propagation. Satellite repeaters have made the signal transmission channel more "stable", but the technical implementation of the reception has not been simplified at all. Here, radio amateurs have a place to apply their knowledge and skills. The article provides a description of an amateur converter, the parameters of which are not inferior to the best examples of industrial production. The converter developed by the author is intended for operation in systems for receiving satellite television in the Ku band (10,95 ... 12,0 GHz) with a single frequency conversion. The converter has the following specifications:
The converter is built according to the scheme of a low-noise frequency converter, structurally combined with an antenna system feed and a built-in input signal polarization switch. Its schematic diagram is shown in fig. 1. It consists of an input waveguide with probes immersed in it (not shown in the electrical diagram), a microwave amplifier made on transistors VT1 - VTZ, a bandpass filter using strip lines L9 - L18, a local oscillator at a frequency of 10,0 GHz on a transistor VT4 with frequency stabilization, a balanced mixer on a VD2 diode assembly, an intermediate frequency amplifier on DA2 and DA3 microcircuits, a voltage regulator on a DA4 microcircuit. It also includes a device on the DA1 chip, which performs the functions of a voltage converter +5 V to -2 V, a switch for polarization and current stabilization of field-effect transistors VT1 - VT3. The converter uses microcircuits, transistors and diode assemblies manufactured by Hewlett Packard (USA).
The input signal, focused by a parabolic mirror, enters the irradiator and from it into a round waveguide with a diameter of 19 mm. The connection of the strip lines of the gates of transistors VT1 and VT2 with the waveguide is carried out using immersed probes installed at an angle of 90 degrees in the waveguide, which makes it possible to receive signals with both vertical and horizontal polarization. Switching the polarization in the converter is carried out by a supply voltage of 13/18 V, supplied via a cable to the output connector XW1. The supply voltage through a divider on resistors R9 - R11 is supplied to the input of the comparator of the DA1 chip. At a supply voltage of 13 V, the DA1 microcircuit turns on the VT1 transistor and a voltage of +1,5 V appears on its drain. At the same time, the VT2 transistor is closed by a negative voltage of -2 V supplied to its gate, and, in addition, the voltage from the drain of this transistor removed. When switching the supply voltage to +18 V, the transistor VT1 closes, and the transistor VT2 turns on in normal operation. This allows you to electronically change the type of polarization of the received signal. The summation of signals from transistors VT1 and VT2 is carried out using a bridge on the strip lines L5, L6. The total signal is fed to the gate of the transistor VT3 - the second amplifying stage. Transistors VT1 - VT3 type ATF36077 have a gain of 12 dB at a frequency of 12 GHz with a supply voltage of +1,5 V and a current of 10 mA. Thus, the total gain of the microwave amplifier is 24 dB with a noise figure of about 0,5 dB. To achieve the best noise figure values, it is necessary to fine-tune the operating mode of the transistors and match their inputs and outputs. In reality, it is possible to obtain a noise figure that differs from the passport one by 0,1 dB, therefore, the maximum value of Ksh at a frequency of 12 GHz is 0,6 dB in the characteristics.
The amplified microwave signal from the drain of the transistor VT3 is fed to the input of the bandpass filter L9 - L18, made on strip interdigital resonators and having a bandwidth of 10,8 ... 12,0 GHz with an uneven frequency response of XNUMX dB. From the output of the filter, the microwave signal is fed to the input of a balanced mixer made on a diode assembly of VD2 microwave diodes with a Schottky barrier and a strip bridge. The other input of the balanced mixer receives a signal with a frequency of 10 GHz from the output of the local oscillator on the transistor VT4. The local oscillator is made on a field-effect transistor according to a common drain circuit, with an open half-wave resonator included in the gate-source circuit of the transistor, and a stabilizing high-quality cylindrical resonator ZQ1 made of titanate-barium ceramics. The signal conversion loss is about 7 dB. The intermediate frequency signal Fpch from the output of the balanced mixer through the filter on the elements L19, C23, C24, R14 is fed to the input of the DA2 microcircuit of the IF preamplifier, made according to the scheme given in the journal Instruments and Experimental Technology, 1984, No. 2, p. 111 (Abramov F. G., Volkov Yu. A., Vonsovsky N. N. "A matched broadband amplifier"). The amplifier on the INA51063 chip has an operating frequency range of 100..2400 MHz with a gain of 22 dB. From the output of the IF pre-amplifier, the signal is fed to the input of the final IF amplifier, made on the DA3 chip and having an operating frequency range of 100 ... 3000 MHz with a gain of 23 dB. Resistors R14, R15, R17 with a resistance of 10 ohms prevent self-excitation of cascaded amplifiers, especially when the load connected to the XW1 connector is mismatched. The converter is powered by a DA4 microcircuit stabilizer, which provides voltage stabilization of +5 V at a current of up to 150 mA. The converter (except for the input waveguide) is made on a printed circuit board (Fig. 2) from double-sided foiled FAF4 fluoroplast 1 mm thick.
The arrangement of conductors and elements on the board is shown in fig. 3.
Attached elements are located on the side of the printed conductors, the foil of the reverse side of the board is used as a common power bus. It is important that all parts have the minimum possible lead length; they must be mounted directly by soldering onto the conductors. To connect the conductors of the common power bus, which are located on the side of the parts, with the foil on the reverse side of the board, a number of metallized holes are drilled in it. The converter uses resistors of the R1-12 type with a dissipation power of 0,125 W. It is possible to use resistors of this type with a power of 0,062 W and resistors P1-8 with a power of 0,125 and 0,25 W. In low-frequency circuits and power circuits, capacitors of the K10-47v type are used. Capacitors C9, C12 and C13 - K10-42. Capacitors in high-frequency circuits, the capacitance of which is not indicated on the diagram (C5 - C8, C15, C17, C22, C24), are made in a "printed" way - their capacitance is formed by plates of a special form of a printed track and a common power bus with the board material as a dielectric. High-frequency connector XW1 type F-75 (available for sale in the radio markets of the CIS countries). Transistors, diode assemblies and microcircuits are from HewlettPackard (USA). As VT4, it is permissible to use transistors AP324A-2 and AP325A-2, transistors VT1-VT3 can be replaced by similar ones manufactured by Siemens, NEC, Philips or AP330A-2 and 3P343A-2, however, in the latter case, the converter noise figure will increase slightly. The HSMS2802 (VD1) diode assembly can be replaced with two KD514A or KD512A diodes, and the HSMS8202 (VD2) assembly with two KA120A or KA120AR diodes. Instead of a 78L05 microcircuit stabilizer, KR142EN5A, KR1157EN501, KR1157EN502 are suitable. When replacing the ZQ1 resonator, TSBN-10 should be used. To connect immersed probes (probe 1 and probe 2) to the gates of transistors VT1, VT2, holes 2 mm in diameter were drilled in the boards, and the foil from the bottom side of the board was removed around the holes within a radius of 2 mm from the center of the installation. The probes are fixed in the body holes (Fig. 4, view A-A) with PTFE bushings 4 mm in diameter and 3,5 mm long. The ZQ1 resonator is glued to the board with a thin layer of glue made from Plexiglas dissolved in dichloroethane. The elements are mounted on the board with a low-voltage soldering iron with a grounded tip solder grades POSK 50-18 or POI. A fully manufactured board with elements installed on it is placed in a cast or milled case (see Fig. 4), the author used a ready-made from a similar product from Microelectronics Inc. The body is made of aluminum alloys (silumin, duralumin, etc.) and is closed on top with a lid (Fig. 5) screwed to the body with M2 screws. A milled or molded cover ensures the separation of the board into compartments and prevents the formation of parasitic feedback and leakage of the local oscillator signal to the input of the microwave amplifier.
When manufacturing a converter in amateur conditions, you can use a simplified version of the case. To do this, on a lathe, according to fig. 4 Turn a flange with a brass waveguide and solder a box for mounting the board, bent from sheet brass, onto it. The lid is also made of sheet brass and partitions are soldered on it in the necessary places to divide the box into compartments. To prevent the excitation of parasitic vibrations in the compartments of the converter to the inside of the cover in those indicated in Fig. In 5 places (shaded areas) pieces of rubber 3 mm thick were glued with an absorbing layer applied to them from a mixture of carbonyl iron powder mixed with BF glue. A hole was drilled in the cover opposite the end of the resonator surface (not shown in the figure, this place is specified after the resonator is installed) and an M5 thread for a brass adjusting screw is cut. It provides tuning of the local oscillator frequency by changing the distance between the screw (case) and the ZQ1 resonator. As the screw moves away from the resonator, the frequency of the local oscillator decreases, and as it approaches, it increases. Therefore, before adjusting the converter, the adjusting screw should only be screwed into the first few threads of the thread.
To seal the converter, a second cover and a rubber gasket are provided, laid in a special groove in the converter body (see Fig. 4). The waveguide flange of the converter is connected to the flange of the irradiator installed at the focus of the antenna using four M4 screws. The waveguide is sealed by installing a rubber gasket in the groove of the converter flange and a 10...20 µm thick fluoroplastic film between the flanges. Drawings of irradiators for direct focus and offset antennas are shown in fig. 6 and fig. 7 respectively.
The converter is configured in the following sequence. A regulated +1...10 V power supply with an output current of at least 20 mA is connected to connector XW100. Set the supply voltage to +13 V and measure the voltage at the terminals of transistors and microcircuits with a voltmeter. Their values should differ from those indicated in the diagram by no more than 10%, otherwise the defective element is replaced. Further, by increasing the supply voltage to +18 V, they make sure that the comparator has switched and a voltage of +2 V has appeared on the drain of the transistor VT1,5, and the voltage has become zero at the drain of the transistor VT1. To check the presence of microwave voltage at the output of the local oscillator, a microwave millivoltmeter is connected to the upper (according to the circuit) output of the resistor R12 (the millivoltmeter described in the Radio magazine, 1995, No. 9, p. 40 is also suitable) and make sure the presence of microwave oscillations. It is not possible to accurately measure the amplitude of the incident wave from the local oscillator, but if the millivoltmeter readings lie within 10 ... 70 mV, the local oscillator works. By connecting a DC millivoltmeter to the left side of the capacitor plate C23 according to the scheme, they check for the presence of a small DC voltage (2 ... 10 mV) at this point of the device. This indicates the operability of a balanced mixer (it is almost impossible to ideally select a pair of diodes and balance the bridge). After that, the converter is closed with the first cover and connected to the antenna feed on one side and to the tuner on the other. By tuning the tuner, one of the received channels is found. The adjusting screw sets the exact value of the local oscillator frequency of 10 GHz + 1 MHz, comparing the received frequency with the known frequency of this channel. The converter is then closed with a second lid and sealed. Author: V. Zhuk, Minsk
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