Small-sized satellite dish pointing indicator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Television antennas

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The devices and devices developed by the designer I. Nechaev receive the warmest response from our readers. Radio amateurs especially liked high-frequency devices that were simple in design - a sweeping frequency generator in the form of an attachment to a conventional oscilloscope, a device for tuning NTV equipment. Since the hobby for receiving satellite programs is becoming the most popular among fans of television technology, at the numerous requests of readers, the author has developed a simple small-sized indicator for pointing parabolic antennas at the satellite, which is convenient to use directly at the antenna installation point.

The small-sized indicator is designed for precise pointing of a parabolic antenna to a geostationary satellite. It works in conjunction with a 11 and 12 GHz band converter with an intermediate frequency range of 0,85 ... 1,9 GHz. The minimum level of the displayed signal is 50 μV. The device is powered, as well as the converter, either from an independent source with a voltage of 12 ... 20 V, or from a receiver of a receiving satellite system via a drop cable.

A feature of this design is selectivity, and unlike the similar one described in [1], it allows not only to tune to the signal maximum, but also to analyze the frequency load of the IF range of the output signal of the converter, which makes it possible to determine with great certainty the satellite to which the antenna has been tuned. This property is very important, since it is elementary to make an initial orientation error of only a few degrees, while the abundance and close positional location of satellites can lead to the fact that you tune not to the desired, but to the neighboring satellite. Therefore, reliable antenna tuning is usually impossible without visual control of the received programs using the receiver and TV, and this, in turn, requires communication between the operator at the antenna and the observer at the TV, which is not always convenient or possible.

The schematic diagram of the device is shown in Fig.1. It is built according to the scheme of a superheterodyne receiver with a zero intermediate frequency. Its microwave part includes a current-controlled generator in the range of 0,85 ... 1,9 GHz, assembled on transistors VT3, VT4 [2], a buffer stage on VT2 and a mixer on VT1. The IF path includes an IF on transistors VT5 - VT7 and a detector on diodes VD1, VD2.

(click to enlarge)

The signal level is indicated by the RA1 microammeter. Sensitivity is operatively regulated by resistor R9.

On transistors VT9, VT10 and a zener diode VD3, a parametric voltage regulator is assembled, on a transistor VT8 - an adjustable current source to power the generator. The frequency of the generator is changed by changing the current using the resistor R17.

The device works as follows. The microwave signal from the output of the converter through the socket XW1 is fed to the input of the mixer - the base of the transistor VT1, at the same time the generator signal is sent to the emitter of this transistor. The IF signal is selected on the resistor R5 and fed to the input of the first stage of the IF on the transistor VT5, then to the level controller on the potentiometer R9, and from it to the final stage on the transistors VT6, VT7.

The IF bandwidth is approximately 0,1 to 10 MHz. And since the receiver has a zero center IF, the total bandwidth is about 20 MHz, which roughly corresponds to the bandwidth of one satellite television channel. Due to the fact that the satellite signal has frequency modulation, its energy is not concentrated on one frequency, but, as it were, "smeared" in a certain frequency band. It is precisely this that the UCH amplifies, and then the signal is detected and fed to the level indicator - the RA1 microammeter.

To create normal working conditions in poor lighting, backlight lamps are included in the device, which are turned on by switch SA2. To control the supply voltage is the switch SA4. It connects the microammeter to the power rail through resistor R21. The converter is powered on by switch SA1, and the operating modes are switched by switch SA3: in its upper position the device is turned off, in the middle position it is powered from an autonomous source (batteries or AC adapter) that is connected to the XS1 socket, and in the lower position power is supplied from the receiver via the drop cable. A converter is connected to socket XW1, and a reduction cable is connected to XW2.

The converter is powered through the L1C4 filter, and when powered from the receiver, the voltage to the device and the converter is supplied through the L2C7 filter.

Structurally, the device is made as follows. It is based on a printed circuit board made of double-sided foil fiberglass with a thickness of 1,5 mm. At the same time, it acts as a front panel, on which most of the parts (except for the UFC parts), all switches, a microammeter, as well as sockets XW1, XW2 (on metal corners) are located. The sketch of the board is shown in Fig.2. Its second side is left metallized and connected by soldering along the contour with a common power bus of the first side.

The UPC is assembled on a separate printed circuit board (Fig. 3). It is attached directly to the microammeter with glue and connected to a common wire in several places.

The following parts can be used in the device: transistors VT1, VT2 - KT3123A-2, KT3123B-2, KT3123V-2; VT3, VT4 - KT3132A-2, KT3132B-2, KT3124A-2, KT3124B-2; VT6, VT7 - KT316, KT315 with letter indices from A to D; VT8 - KP302B, V, KP307A; VT9 - KT815, KT816 with letter indices from A to G and similar; VT10 - KP303G, KP303D.

In the microwave part, it is necessary to use packageless capacitors - K10-17, K10-42 and high-frequency resistors S2-10, RN1-12, in the rest you can use KM, KLS and similar imported ones. Trimmer resistor - SPZ-19, variables - SPO, SP4. Fixed resistors - MLT, S2-33.

Coils L1 - L3 are wound with PEV-2 0,4 wire on a 3 mm mandrel and contain 7 ... 9 turns each. Coils L4, L5 are made in the form of strip lines (see Fig. 2) - they are similar to those that were described in detail in [2]. Coil L6 is a normalized choke type DM-0,1, its inductance can be selected in the range of 200 ... 500 μH.

Diodes - any high-frequency low-power, preferably germanium or with a Schottky barrier, a zener diode - low-power for a stabilization voltage of 10 ... 12 V.

Switches and socket XS1 - any small-sized, incandescent lamps - SMN 6,3-20, microammeter - M4762-M1 with a total deviation current of 200 μA.

When mounting the microwave part, the leads of the parts must be made as short as possible. If you use a case of a different configuration, then the printed circuit board can be remade by making it in any form (except for the microwave part).

The adjustment should begin with setting up the microwave generator. To do this, it is better to use a frequency meter with an operating frequency of up to 2 GHz, it is connected to the collector of the transistor VT2. In the left position of the resistor R17 according to the diagram, by selecting the resistor R16, the lower limiting tuning frequency is set, and the tuning range is selected by choosing the value of the resistor R17. In the author's copy of the device, the generator frequency changed from 700 MHz to 2 GHz when the current through the transistors VT3, VT4 changed from 13 to 0,8 mA. To get a smoother setting, you will have to choose a resistor R17 with a small jump in the initial resistance and a logarithmic characteristic.

If you do not have a frequency meter, you can use the receiver for tuning. To do this, its input is connected to the input of the device (socket XW1). The receiver is tuned in frequency, and the generator is tuned to the same frequency with the resistor R17, the moment of tuning is determined by the appearance of a signal in the form of interference on the TV screen. Thus, it is possible to calibrate the scale of this resistor.

Then the resistor R9 is set to the upper position according to the diagram and the resistor R18 sets such a level of intrinsic noise so that the pointer of the pointer device deviates slightly. After that, it is desirable to check the sensitivity and tuning range using a measuring microwave generator. If this is not possible, you must connect the device to a converter installed on a tuned antenna. The noise should increase, and after that, by tuning the device in frequency, they tune into satellite channels.

If the arrow goes off scale, then the gain must be reduced with resistor R9. Having tuned in to a weak signal, far removed from the more powerful ones, by selecting the resistor R3, maximum sensitivity is achieved. For ease of use, marks are made on the scale for the most frequently received satellite television programs, for example, NTV Plus or Eurosport, for different polarizations. It happens that without being connected to the converter, the arrow constantly goes off scale at any position of R9 or goes off scale in certain parts of the range - this means that, most likely, the device is self-excited. You will have to carefully carry out the installation, reduce the length of the connecting wires and, possibly, increase the capacitance of the blocking capacitors.

If there is a measuring generator, the scale of the device can be calibrated in units of voltage, in which case the resistor R9 must be replaced with a switch with a resistive divider, which will act as a fixed attenuator.

Literature

1. Zhuk V. Antenna pointing indicator to the satellite. - Radio, 1994, No. 12, p. 4, 5.
2. Nechaev I. Prefix-GKCH for the ranges of 300 ... 900 and 800 ... 1950 MHz. - Radio, 1995, No. 1, p. 33.
3. Nechaev I. A device for tuning NTV equipment. - Radio, 1998, No. 3, p. 10 - 12; No. 4, p.14, 15.

Author: I. Nechaev, Kursk

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