Panoramic view on TV. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Телевидение

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Many models of modern TVs use channel selectors with electronic tuning SK-V-1C. SK-V-2S, SK-M-E, SK-M-23 and SK-D-22. The varicaps of these selectors are supplied with a constant voltage, which lies in the range from 0 to 25 ... 28 V (depending on the channel number). In such TVs, it is relatively easy and simple to make a panoramic view of the television ranges and adjust the panorama to the desired channel. To do this, it is necessary to form a voltage of the required form, varying from 0 to 25 ... 28 V, from the sawtooth voltage taken from the vertical scanner, and apply it to the varicaps of the channel selector.

As a result, the selector setting in any of the subbands changes from the upper frequency to the lower one with the frame rate of the TV. Consequently, the brightness of the kinescope screen, when the beam moves from top to bottom, depends on the presence of signals from television transmitters operating in the selected subband. Dark horizontal stripes appear on the screen, the width of which is proportional to the bandwidth of the IF image amplifier (IPGA) in the TV. On fig. As an example, Figure 1 shows the panorama of received signals in the high-frequency subband (6-12th channels) of meter waves, observed in Moscow on the TV screen "Electronics-450". Moreover, the difference between the signals of the image and sound is quite noticeable. The bands from image signals (out) are lighter than those from sound signals (sound).

To set up a TV with a panoramic view, you need to get a mark visible on the screen corresponding to the tuning voltage regulated by the controls available on the TV. For this purpose, the tuning voltage is compared with the sawtooth voltage applied to the varicaps, and the necessary signal is formed. The tuning mark is displayed on the TV screen along with stripes from working transmitters and differs from them in shape and brightness: this is a thin white line, conventionally shown in Fig. 1 black.

Ris.1

It is advisable to use a panoramic view with tuning in TVs with touch channel switching, in which there are no tuning scales on the front panel, and the scales available in the touch switches are small and inconvenient to use. Panoramic view allows you to equip the TV with a convenient and large tuning scale, the length of which is equal to the height of the screen. The boundaries of the received channels for each subband can be applied to the side edges of the screen frame.

On fig. 1 shows an example of the location of the scale of the low-frequency (channels 1-5) and high-frequency (6-12th channels) subranges of meter waves for panoramas observed in Moscow on the TV screen "Electronics-450" (channel selector SK-M-E) . On TVs with SK-V-1 channel selectors, the panorama and scale of the high-frequency subrange (6-12th channels) will be the same. Next to this scale, you can place a scale for the range of decimeter waves, and instead of one subrange scale for channels 1-5, there will be two: for channels 1-2 and 3-5.

After switching the TV to panoramic view mode and tuning, the touch switch is used to switch subbands, and the variable resistors in the switch are used to tune to the desired program.

On a TV with a panoramic view, you do not need to blindly switch all the sensors in a row in search of working transmitters, but you can immediately turn on the desired program. To do this, mobile tags with program numbers are attached next to the scale between the channel boundaries. In addition, on such large scales, you can even fine-tune the TV to a given channel. The indication accuracy is high due to this. that the tuning mark can be made many times thinner than the bandwidth from the transmitters.

It is convenient to use panoramic views and settings outside the zone of reliable reception, where the passage of signals from received television transmitters is irregular. On the TV screen, you can see in which part of the subband the transmission has improved, and where the signals have weakened. After that, you can immediately turn on the desired channel with a strong signal. And finally, a panoramic view can be used with great success in setting up and orienting antennas in the presence of interference from television transmitters operating on adjacent channels and from other sources. The antenna is oriented, achieving the disappearance of marks from interference sources and the most clear display of the bands from the received signals of television transmitters. In this case, it is clear in which part of the subband the interference is most intense, and you can even determine their frequency.

You should be aware that the capacitance of the varicaps used in channel selectors with electronic tuning, depending on the applied voltage, changes non-linearly, i.e., low voltages correspond to large capacitance values ​​and a fast change, and vice versa. Therefore, if a sawtooth linearly changing voltage is applied to the varicaps, then on the TV screen the bands from transmitters operating in the low-frequency part of the subbands will be thickened, and in the high-frequency part they will be sparse. In order for the stripes to be evenly spaced on the screen, the voltage applied to the varicaps must be non-linear and, at low values, it must change more slowly, and at large values, it must change faster. To this end, the increasing sawtooth voltage taken from the vertical scanner must be amplified to an amplitude of 25 ...

Schematic diagram of the node that generates the required sawtooth voltage and mark signal is shown in fig. 2. The sawtooth voltage is amplified and inverted by the cascade on the transistor V1 and differentiated by the C1R3R4 circuit. In the cascade on the transistor V2, assembled according to the emitter follower circuit, the voltage is limited and through the switch S1.1 it goes to the varicaps of the channel selector. The repeater is powered by a stabilized voltage supplied to the TV set to variable tuning resistors. Therefore, the voltage at the emitter of the transistor V2 cannot become more than 28 ... 30 V, which eliminates the possibility of breakdown of the varicaps. The SI switch on the varicaps is supplied with either the previous tuning voltage (in the "Programs" position), regulated by variable resistors in the TV, or the generated voltage (in the "Overview" position).

Ris.2

The sawtooth voltage through resistor R6 acts on the Schmitt trigger on transistors V4 and V5. The tuning voltage also comes to the trigger through the resistor R10 from the output of the inverter on the transistor V3. When it is adjusted, the trigger fires at various sawtooth voltage levels. As a result, a narrow pulse is formed at the output of the node after the capacitor C3, which enters the video amplifier and forms a tuning mark on the kinescope screen. Switch S1.2 in the "Programs" position closes the trigger input and excludes the appearance of a mark on the received image. In the review and setup mode, switch S1.2 closes the input of the TV's clock selector. This eliminates the synchronization of the sweep master generators by various pulses generated at the output of the radio channel when all possible carrier frequencies fall into the UPCH passband during a panoramic view of the subbands. Thus, irregularities and curvature of the vertical borders of the raster, which interfere with the observation of bands from TV transmitters, are eliminated.

When the node is connected to the Elektronika-450 TVs, the increasing sawtooth voltage to the base of the transistor V1 can be removed from the output of the deflection system frame coils, which is not connected to a common wire. The contacts of the switch S1.1, connected to the TV circuits, are included in the break of the wire going to the engine of the variable R2 setting resistor of the TV (with a fixed contact to the resistor). The switch contact S1.2, connected to the TV, is connected to the base terminal of transistor T8 of block A2, and the terminal of capacitor C3 is connected to the emitter terminal of transistor T4 of the output stage of the video amplifier. A voltage of 28 ... 30 V is supplied from the zener diode D4 of block A3, and a voltage of 70 V is supplied from pin 14 of the same TV block.

In the Electronics Ts-430 TVs, the sawtooth voltage is removed from the output of the collector of the transistor T9 of the vertical scan module, while the resistor R1 of the node is disconnected from the common wire and connected to the point to which the voltage is supplied - 12 V, feeding this module. Switch S1.1 is included in the break of the wire connecting pin 13 of the channel selector with socket 10 of connector X2 of block A5 on the TV. The switch contact S1.2 is connected to the output of the base of the transistor T2 of the vertical scan module, and the output of the node with the output of 3 microcircuits D1, D2 or D3 (depending on the desired color of the label) of the module A7. Voltage 28...30 V can be supplied from slot 10 of connector X1 of the power supply.

The sawtooth voltage in TV sets of the UPICT-32-GU series is obtained from pin 4 of the 2X2 connector of the vertical scan module. The contacts of the switch S1.1 of the node are included in a break in the wire connecting socket 2 of the X12b connector with socket 9 of the X2b connector (the latter is connected to the movable contact of the switch). The contact of the switch S1.2 is connected to the output of the base of the transistor T2 of the module MZ-1 (AR3), and the output of the node is connected to the output of the emitter of the transistor T3 of the module A9, A 10 or A11. The voltage of 28...30 V is removed from the zener diode D1 of the M5-3 board of the program selection unit.

And finally, in TVs of the UPIMTST-61-I series, an increasing sawtooth voltage is obtained from the output of the emitter of the transistor T8 of the vertical scan module. The contacts of the switch S1.1 of the node are included in the break of the jumper connecting the contacts 8 of the presetting board and the SVP block (contact 8 of the latter is connected to the movable contact of the switch). The switch contact S1.2 is connected to terminal 7 of the MZ-1 (AR1) module, and the output of the node is connected to the output of the emitter of the transistor T3 of the module A9, A 10 and A11 (depending on the desired color of the label). Voltage 28 ... 30 V is removed from pin 5 of the Sh-P2 connector of the SVP block.

In the TVs "Electronics Ts-430", as well as the UPIMTsT-61-II, and UPITST-32-IV series, a voltage of 70 V is obtained from an additional stabilizer on the KS568 or D817B zener diode by applying one of the voltages 220, 190, 150 or 120 to it In, available in these TVs, through a resistor with a resistance of 16 kOhm and a dissipation power of 2 watts. The voltage of 10 ... 12 V, generated in the power supply of all TVs, is removed from any point convenient for this.

The assembly details can be placed, as done by the author, on a part of the board used in computer technology devices for mounting integrated circuits. The scheme for connecting parts to the sites of such a board and connecting them to each other is shown in Fig. 3.

When establishing a node, first, by selecting a resistor R1, they ensure that the amplitude of the sawtooth voltage on the base of the transistor V2 reaches 25 ... Resistors R28 and R6 affect the coincidence of the tuning mark with the bands from television transmitters. Therefore, aligning the tuning mark with the strip from the transmitter, set the switch S10 to the "Programs" position and make sure that the image and sound of the selected program are normally received. If there is no reception at all, then the specified resistors are selected. The selection of the resistor R13 has a greater effect on the boundaries of the label movement on high-frequency channels, and the resistor R1 - on low-frequency channels.

Good image and sound reception should be obtained in the position of the tuning mark near the low-frequency band edge from the television transmitter. By selecting capacitor C3, you can change the pulse duration, and therefore the thickness of the tuning mark on the TV screen.

Author: S.Sotnikov, Moscow; Publication: N. Bolshakov, rf.atnn.ru

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