A device for setting up NTV equipment. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Television antennas

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The reception of television programs through satellite transponders has become the sign of the day today. The number of satellites in geostationary orbit and the number of programs on each of them is increasing. Buying an NTV reception system in a store is no longer a problem, and its prices are dropping. Having bought factory-made equipment, many radio amateurs experiment with it. We also have enthusiasts who make such equipment themselves. Here we publish a description of a simple device for optimal tuning of all components of the NTV receiving system.

The reception of television programs through satellite repeaters is of interest to a growing circle of readers. With the launching into geostationary orbit of satellites of direct television broadcasting systems (NTV), for example. "Hals" and "Not Bird", such a reception has become available to many residents of our country (low cost of equipment, small dimensions of the antenna). At the same time, other satellites are also of interest to radio amateurs, the signal from which is much weaker, and in order to obtain a satisfactory reception quality, large antennas must be used.

One of the problems that have to be solved in these experiments is debugging the antenna system and tuning it to the required satellite for the maximum signal. For NTV systems using relatively powerful transmitters, this problem is easily solved, since it is possible to use antennas with a small diameter of a parabolic mirror. For such antennas, the width of the radiation pattern is several degrees, so small inaccuracies in pointing it are quite acceptable and will not even have a very strong effect on the final result. Another thing is when a large antenna is used and weak signals are received. In this case, very careful and careful tuning is required.

The combined instrument described below will help to significantly reduce the complexity of this process, simplify and make it visually clear, which, in combination with an oscilloscope, can be used as a panoramic indicator of the spectrum of the frequency range 0,8 ... 2 Hz or an indicator of the frequency response of this range, and without an oscilloscope - as signal level indicator in any area or immediately in the entire range. With the help of the device, you can quickly assess the health of the converter by the noise level, check the performance of the tuner, if necessary (if, for example, it is self-made or works for a long time), adjust the frequency response and tuning range. The device will help you quickly tune in to satellite signals and adjust the antenna system to the maximum signal, clarify the location of the converter (feeder), adjust its polarization, etc. The main convenience lies in the fact that the results of the manipulations are immediately reflected on the oscilloscope screen or dial indicator.

The scheme of the device and its design are quite simple and accessible for manufacturing by radio amateurs of average qualification. The block diagram is shown in Fig.1. It consists of a current-controlled oscillator (G1) - a microwave generator with a tuning range of 0,8 ... 2 GHz, a buffer amplifier A 1, from the output of which a signal on a scale of 1; 1 goes to the output "GKCH 1:1", and through the resistive attenuator A2 - to the output "GKCh 1:10". A triangular voltage driver (G2) and a voltage-to-current converter - (U1) are designed to control the generator. The upper and lower frequencies of the swing range are set independently of each other using variable resistors, which is convenient during operation. Amplifier AZ serves to supply a signal to the sweep of the oscilloscope. These nodes are powered by a mains power supply (U2).

These elements, together with the detector head, provide a panoramic indication of the frequency response. To do this, the input "Y" of the oscilloscope is fed a signal from the output of the detector head, and the input "X" is a sweep signal from the output of the amplifier AZ. To implement the spectrum analyzer mode, the device has a mixer (U3), to which the signal from the generator passes from the "GKCh" output through the "GKCh" input, and the signal from the output of the microwave converter through the "IF" input. The output signal of the mixer is amplified by video amplifiers (A4 and A5), detected by an amplitude detector (U4), from the output of which the signal can be fed either to the "Y" input of the oscilloscope or to a dial indicator. The device has sockets for powering the converter. The spectrum analyzer operates with the so-called "zero IF", which made it possible, with satisfactory quality, to simplify the construction of the device. Structurally, the device is made of four main components: a high-frequency unit, a control voltage and current driver, a video amplifier, and a power supply. Each of the blocks is assembled on a separate printed circuit board. This made it possible to manufacture and regulate them separately from each other, and only then install them in the instrument case.

The scheme of the high-frequency unit is shown in Fig.2. On transistors VT1 and VT2, a microwave generator is made, the generation frequency of which can be controlled using current, and on VТЗ - a buffer amplifier. Signals from the output of the amplifier are fed to sockets ХS1 "1:1" and ХS2 "1:10". These nodes were described in more detail earlier in [1].

A signal mixer is assembled on the VT4 transistor, it works in the spectrum analyzer mode. A signal from the microwave converter arrives at its base through the XS3 socket, and the signal from the generator arrives at the emitter through the XS4 socket. To do this, sockets XS1 and XS4 are connected with a coaxial cable. The difference signal is taken from the collector of the transistor VT4 and then fed to the input of the video amplifier, while the capacitor C14 suppresses the high-frequency components of the difference signal. The microwave converter is powered through a low-pass filter L2C3.

The scheme of the shaper of the control voltage and current is shown in Fig.3. A triangular voltage driver is assembled on the DA1 - DAZ and DD1 microcircuits, which works in conjunction with a controlled current stabilizer on the DA4 microcircuit and the VT5 transistor. An oscilloscope sweep signal amplifier is assembled on the DA5. The amplitude of this voltage can be adjusted by a variable resistor R27. Resistors R17 and R20 set, respectively, the lower and upper frequencies of the swing frequency range of the microwave generator. This node is made according to the scheme [2] and therefore is not described in detail here either.

The video amplifier circuit is shown in Fig. 4. He is two-stage; each of them is made on a high-speed op-amp. The gain of each stage is 38...40 dB, which provides the required sensitivity of the spectrum analyzer. Gain adjustment is carried out by a variable resistor R32.

At the input of each stage, high-pass filters C19 R29 and C23 R33 are installed, which are designed to reduce the effect of low-frequency interference and interference. There is no special high-pass filter in the video amplifier. its role is played by the op amps themselves, which provide the through bandwidth of the analyzer of several hundred kilohertz. At the output of the second stage, a detector diode VD2 is installed, which cuts off the negative half-waves of the signal, and positive half-waves of the alternating voltage of the signal are fed to the input "Y" or a pointer indicator.

The power supply is assembled according to the traditional scheme (Fig. 5) and contains a step-down power transformer T1, a full-wave rectifier on a diode matrix VDZ and smoothing capacitors C27 and C28. Voltage stabilizers are made according to a well-known scheme and do not need comments.

The scheme of board-to-board connections is shown in Fig.6. The device is switched on by the SA1 switch, and the operating modes are switched by the SA2 switch. These switches, as well as variable resistors R17, R20, R27, R32, are located on the front panel of the device. And in fig. 7 shows a diagram of the detector head. Its main purpose is to detect a microwave signal.

As mentioned above, the device can be used as a frequency response indicator, spectrum analyzer or signal level indicator. In the first case, the device works in conjunction with an oscilloscope that has an "X" input. A signal is fed to its input from the output XS6 ("Exit X") of the device and the sweep is set to full screen. In this case, a luminous horizontal line, called "zero", will appear on the oscilloscope, which is set to the bottom line of the screen grid.

The output of the detector head is connected to the input "Y" of the oscilloscope, and its input is connected to the output socket XS1 ("GKCh output 1: 1"). In this case, an inclined or somewhat curved line will appear on the screen, the height of which in relation to the zero line will be proportional to the signal level of the microwave generator, this line will be the reference line. Then the detector head is connected to the output or to the control point of the device under study, and the signal from the XS1 socket ("GKCh output" 1; 1 or 1:10) is fed to the input of the device. By comparing the position of the reference line and the line obtained in this case, one can judge whether the microwave signal passes through this device or not, whether the signal is amplified or attenuated in it, and also what its frequency response is. So you can check the health of tuners, amplifiers, signal splitters, etc. The range in which these parameters are studied is set by resistors R17 and R20 (shaper unit, Fig. 7) and can range from several tens of MHz to the full range. In this mode, the mixer and video amplifier do not work because they are not powered.

In the spectrum analyzer mode, all components of the device work, the XS1 and XS4 sockets are connected by a cable, and the output of the microwave converter is connected to the XS3 socket ("IF Input"). In this case, a blurred line, the so-called "noise track", should be observed on the oscilloscope screen. After applying the supply voltage to the converter (jack XS5), the noise level should increase significantly, its amplitude can be adjusted by resistor R32 (video amplifier unit).

When moving the antenna in space at the time of tuning to the satellite, bursts of a noise-like signal will appear on the oscilloscope screen - at the sweep point that corresponds to the frequency of this signal. With the help of variable resistors for setting the frequency swing range, this signal can be "expanded" to full screen. After that, you can tune the antenna system, change the polarization and installation angles until the maximum amplitude of the received signal is obtained. This setting allows you to "squeeze" the maximum possible out of the system. By the distribution of signals in the frequency range and their relative power, it is determined which satellite the antenna is tuned to. If in this mode, a pointer measuring indicator is connected to the "Output Y" of the device, for example, a microammeter with a total deflection current of 100 μA. then by the deviation of the arrow one can judge the change in the level of the received signal, which means that it will be convenient to tune the antenna system to the maximum signal.

A sketch of the printed circuit board of the high-frequency part is shown in fig. 8. It is made of double-sided foil fiberglass. The conductors are located on one side of it, and the other is left metallized (it serves as a screen) and is connected along the contour to the common power bus of the first side. The board is placed on the side wall of the device housing and is attached to it with four output microwave sockets. This ensures a minimum distance between the high-frequency connectors and the elements on the board.

Sketches of printed circuit boards of the shaper, video amplifier and power supply are shown in fig. 9, 10 and 11. For their manufacture, one-sided foil material can be used. These boards are then placed at the bottom of the device case on a metal plate (or one-sided foil fiberglass, getinax), which acts as a common wire and to which the common power buses of all boards are connected.

It is permissible to use elements of the following types in the device: microcircuits DA1 - DA5 - K140UD6, K140UD7, DA6.DA7 - K544UD2A, K544UD2B, DD1 - K561TM1 or others containing an RS flip-flop. Transistors VT1 - VT4 - KT3124A - 2, KT3124B - 2, KT3124V - 2, KT3132A - 2, KT3132B - 2, KT3132V - 2; VT5 - KT608A, KT608B, KT603 with letter indices from A to G, KT503 (A - E); VT6 - KT603(A - G), KT608A, KT608B, KT602A, KT602B; VT7 - KT315(A - I), KT312(A - B), KT3102(A - E); VT8 - KT208(A - M), KT209(A - M); VT9 - KT208 (A - M), KT209 (A - M), KT203 (A - B), KT361 (A - E).

Diodes VD1 - KS156A; VD2 - D9 with any letter index, D18, D20, D310, D311A, D311B, D312A, D312B; we will replace the VD3 bridge with four diodes of the types KD102B, KD103B, KD105B, KD106A, KD509A, KD510A; VD4, VD5 - D814G, KS211Zh, KS211Ts, KS510A; LED HL1 - AL307 with letter indices from A to G or AL341 (A - D) - oxide K50-6, K50 - 24, K53 - 1; as C1 - C14 it is desirable to use frameless K10 - 42, K10 - 17 or similar, in their absence (as an extreme case), KM, KD with the minimum possible length of the leads are suitable; the rest - KLS, KD, CT, KM.

Variable resistors - SPO, SP4, SP of any modification, tuning (R6) - SDR - 19, the rest - MLT, S2-33. In the high-frequency part of the device design, it is desirable to use resistors C2 - 10.

Inductor L2 - DM - 0,1 with an inductance of 20 - 100 μH. A step-down transformer is any small-sized one that has two secondary windings for a voltage of 12 ... 15 V at a current of up to 70 mA.

In the detector head it is necessary to use microwave detector diodes, capacitors, as in the high-frequency part of the device, and resistors C2 - 10.

Setting up the device begins with adjusting the operation of the individual boards of the device. The power supply usually does not need to be configured. You only need to check its performance - the output voltages should be within 11 ... 13 V. If you plan to power the converter from the same power supply, then you need to power it up a bit - the transformer must provide current up to 200 mA; the stabilizer will work the same, only the VT6 transistor, if it starts to get very hot, you may have to place it on a small radiator.

The control voltage driver is preliminarily checked as follows. Resistors R16 - R21 are connected to the board, which are located on the front panel. Board outputs 2 and 4 are temporarily closed, and an additional 200 Ohm resistor is installed between them and the common wire, after which supply voltages are applied. When the resistors R17 and R20 are rotated on an additional resistor, triangular oscillations are checked with an oscilloscope, their maximum amplitude must be at least 1 ... 1,5 V.

Then they check the video amplifier board - it should not be excited in any position of the R2 resistor slider. If this happens, then you may have to parallel the capacitors C20. C21, C25, C26 install ceramic capacitors with a capacity of 0,047 - 0,1 uF. If such a connection does not give a positive effect, it is necessary to increase the capacitance of capacitors C22, C24 by two to three times. The gain of the video amplifier at a frequency of approximately 50 kHz should be several thousand times.

The setting of the high-frequency board is carried out in the following sequence. A supply voltage (1 V) is supplied to pin 12 of the board, and voltage from an adjustable stabilized power supply is supplied to pin 2. A frequency meter operating in the range of 1 ... 0,7 GHz is connected to the XS2 socket. A voltage of 2 V is applied to pin 0,5 and, gradually increasing it, they achieve the moment of generation. Then, a constant voltage is controlled at pin 3 and, by changing the voltage at pin 2, the voltage at pin 3 is fixed, corresponding to the lower 0,7 ... 0,9 GHz and upper 1,9 ... 2,1 GHz generation boundaries. It is within these limits that the voltage on the engines of resistors R17 and R20 should change. Such voltage values ​​\u16b\u18b(with a small margin) are then set by selecting the values ​​​​of resistors R17, R19 for resistor R21 and R20, RXNUMX - for resistor RXNUMX. It should be noted that as the voltage decreases, the generated frequency increases.

After that, all the boards are placed in the case, while, as mentioned earlier, the high-frequency board is mounted on the side wall of the case, and the rest are placed on a metal or metallized base with dimensions of 90x120 mm and are attached to it with glue, as well as by soldering ground mounting pads with a thick tinned wire. base boards. In addition, the high-frequency board must be connected along the bottom edge with the base using a strip of tinned copper foil. The base itself is attached to the bottom of the case with screws, while it is better to use a metal case, its dimensions can be (approximately) 50x105x140 mm. All controls are placed on the front cover, and sockets XS5 - XS7 - on the back side.

Having finished adjusting the boards individually, you can begin to calibrate the scales of variable resistors. To do this, the device is turned on in the "Analysis" mode and an oscilloscope is connected to it. A narrow noise track should be observed on the screen, it should be made horizontally slightly smaller than the screen size. Then, a signal with a frequency of 3 ... 1,2 GHz with a level of -1,5 ... 30 dBm from the measuring generator (with a tuning range of 50 ... 0,8 GHz) is fed to the IF input (jack XS2). The instrument is set to maximum frequency sweep mode. Approximately in the middle of the screen, a signal in the form of an amplitude burst should appear. When you change the frequency of the generator, it will begin to move around the screen. Then the signal level of the measuring oscillator is reduced to the minimum, at which the signal is still observed on the screen, and the trimming resistor R6 is used to achieve its maximum level.

The generator signal level is increased several times and the frequency is set exactly, for example, 1,5 GHz. Variable resistors R17, R20 are provided with pointers and, having shifted the signal on the screen exactly to the left edge of the scan with the resistor R17, make a corresponding mark on the scale of this resistor. Similarly, but with resistor R20, the signal is shifted exactly to the right edge of the sweep and a mark is made on the scale of this resistor. Alternately, other values ​​​​of frequencies are set on the measuring generator, and the calibration process is repeated.

Literature

1. Nechaev I. GKCh prefix for the ranges of 300 ... 900 and 800 ... 1950 MHz. - Radio. 1995, No. 1, pp. 33, 34.
2. Nechaev I. Prefix for measuring frequency characteristics. - Radio, 1994. No. 1, pp. 26, 27.

Author: I. Nechaev, Kursk

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