Prefix for receiving TV programs in cable subbands. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Телевидение

 Comments on the article

Cable television networks broadcast on-air programs not only on MB channels, but also on cable subband channels. The author of the published article tells about a simple way to receive them on old TVs.

In recent years, in the homes of many districts of Moscow and other cities, television broadcasting programs have been received through local cable networks. In addition to the terrestrial programs of the MB band, sent over standard channels 1 to 12, many new TV programs have appeared in the frequency bands of the so-called cable sub-bands. They are located between channels 5 and 6, in the range of 110 ... 174 MHz (channels K1 - K8), as well as between channels 12 (MB) and 21 (UHF) in the intervals of 230 ... 294 MHz (channels K11 - K18) and 294 ... 470 MHz (Hyperband subband, channels K20 - K41). Programs appeared as a result of converting signals transmitted over UHF channels into channels of meter and cable subbands. This is because many cable networks (with a bandwidth of up to 500 MHz) cannot yet transmit signals at all UHF frequencies, although ultra-wideband cables (up to 1000 and 2500 MHz) and fiber optic lines already exist.

Standard channel selectors SK-M-24-2, SK-V-1, SK-M-15, etc. .), do not allow you to receive programs in these subbands. This is due to the fact that the control voltage of the varicaps of the listed selectors can vary from +4 ... 28 to 27 ... 0,7 V. In order to be able to receive these programs, it is proposed to shift the lower limit of the control voltage to zero and even small negative values. This makes it possible to considerably expand the tuning range of such selectors towards lower frequencies due to a significant increase in the capacitance of the varicaps.

Such a shift is provided by the simplest prefix, the scheme of which is shown in Fig. 1. In the same place, in a simplified form, the circuits of the channel selector (SC) and the program selection device (UVP) are shown. The numbering of parts in UVP is given for the USU-1-15 standard block. In the lower, according to the scheme, position of the engine of the tuning resistor R70 (lower frequency of the subrange), the voltage at the UVP output can have a value in the range of 0,5 ... 1 V, depending on the UVP model. When the set-top box is connected, the voltage at point "A" decreases to zero and even to small negative values, which depends on the position of the setting resistor R1 slider.

Therefore, by tuning to the lowest frequency, for example, sub-band III (channels 6-12), or by setting the switch to the sixth channel (for ULPCT) and connecting the set-top box, you can receive cable TV programs in the interval between channels 5 and 6 MB.

The set-top box can be made as a separate unit, but it is quite possible to integrate its elements into the TV. The length of the connecting wires with the nodes of the device (there are only two of them) does not matter. The resistance of the tuning resistor R1 can be in the range of 22 ... 100 kOhm. Due to a sharp change in the capacitance of the varicap, it is advisable to make it up from two resistors with significantly (tens of times) different ratings: one for coarse tuning, the other (with a lower rating) - multi-turn (for example, C5-2) for fine.

To connect the set-top box, a contact was used in the form of a tube made of tin, bent along the diameter of the pin on the TV board: for the selector SK-M-24-2 - pin 4, for SK-D-24 - 5, for SK-V-1 - 8, for SK-M-15 - 5, i.e. "Setting" contact for any other selector. The conductor from the common wire of the set-top box was equipped with a Crocodile connector. Switch SA1 - any. When embedding the elements of the set-top box in the TV, the wire coming from its switch can be soldered at the desired point. Do the same with the second wire.

In order not to rebuild the tuning resistor each time, you can turn on several tuning circuits in parallel and turn them on with a switch as shown in Fig. 2. Switch SB1 - P2K with a free button to turn off the set-top box or PG with a position for the same purpose.

The use of such a set-top box made it possible to receive all 15 programs transmitted by the Teleinform cable network in our area (Marino). The possibility of receiving channels in another subband when rebuilding the TV to the 21st channel of the decimeter range was not checked, since the programs transmitted over the air had already been received.

Author: N.Mamarygin, Moscow

See other articles Section Телевидение.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Alcohol content of warm beer 07.05.2024

Beer, as one of the most common alcoholic drinks, has its own unique taste, which can change depending on the temperature of consumption. A new study by an international team of scientists has found that beer temperature has a significant impact on the perception of alcoholic taste. The study, led by materials scientist Lei Jiang, found that at different temperatures, ethanol and water molecules form different types of clusters, which affects the perception of alcoholic taste. At low temperatures, more pyramid-like clusters form, which reduces the pungency of the "ethanol" taste and makes the drink taste less alcoholic. On the contrary, as the temperature increases, the clusters become more chain-like, resulting in a more pronounced alcoholic taste. This explains why the taste of some alcoholic drinks, such as baijiu, can change depending on temperature. The data obtained opens up new prospects for beverage manufacturers, ... >>

Major risk factor for gambling addiction 07.05.2024

Computer games are becoming an increasingly popular form of entertainment among teenagers, but the associated risk of gaming addiction remains a significant problem. American scientists conducted a study to determine the main factors contributing to this addiction and offer recommendations for its prevention. Over the course of six years, 385 teenagers were followed to find out what factors may predispose them to gambling addiction. The results showed that 90% of study participants were not at risk of addiction, while 10% became gambling addicts. It turned out that the key factor in the onset of gambling addiction is a low level of prosocial behavior. Teenagers with a low level of prosocial behavior do not show interest in the help and support of others, which can lead to a loss of contact with the real world and a deepening dependence on virtual reality offered by computer games. Based on these results, scientists ... >>

Traffic noise delays the growth of chicks 06.05.2024

The sounds that surround us in modern cities are becoming increasingly piercing. However, few people think about how this noise affects the animal world, especially such delicate creatures as chicks that have not yet hatched from their eggs. Recent research is shedding light on this issue, indicating serious consequences for their development and survival. Scientists have found that exposure of zebra diamondback chicks to traffic noise can cause serious disruption to their development. Experiments have shown that noise pollution can significantly delay their hatching, and those chicks that do emerge face a number of health-promoting problems. The researchers also found that the negative effects of noise pollution extend into the adult birds. Reduced chances of reproduction and decreased fertility indicate the long-term effects that traffic noise has on wildlife. The study results highlight the need ... >>

Random news from the Archive New IC Series S1R77000 13.02.2005 EPSON CORPORATION's new S1R77000 series of ICs includes four analog input ICs for scanners, multifunction printers, faxes, and other scanning applications. The microcircuits include components such as automatic level control, quantization, and analog-to-digital conversion. There are CCD sensors along with sweep generators for them.

Other interesting news:

▪ NCP4589 Auto Power Saving LDO Regulator

▪ Wireless mouse building kit from TI and Cypress

▪ organic meteorite

▪ Soil houses

▪ High-speed Internet between the Earth and the Moon

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Consumer Electronics. Selection of articles

▪ article The road to the temple. Popular expression

▪ article On the satellite imagery of which Ukrainian city can you see the number 666? Detailed answer

▪ Article Quick key. home workshop

▪ article New life for old clocks. Encyclopedia of radio electronics and electrical engineering

▪ article Low battery indicator. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024