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| Direct-to-home television Deepak Bagai MODERN cable television networks deliver “bouquets” of programmes, many of which are “free to air” and some are “paid”. The Government of India has recently given concurrence to the implementation of direct-to-home television broadcasting. In this technology the high-density TV signals in the Ku band are directly beamed from the satellite to the user’s home. Building tips NEW PRODUCTS & DISCOVERIES
UNDERSTANDING THE UNIVERSE |
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Direct-to-home television In its simplest form, TV channels would be transmitted from the satellite to a small dish antenna mounted on the window or the rooftop of the subscriber’s home. The user will be able to scan about 700 channels and the broadcasters of DTH TV shall be able to cover even the remotest of areas. In DTH, the payments will be made directly by the subscriber to the satellite company offering the service. A DTH network consists of a broadcasting centre, satellites, encoders, multiplexers, modulators and DTH receivers. The broadcasting centre is a complete studio in itself with an additional facility of satellite uplink. DTH service provider shall have to lease Ku-band transponders from the satellite. The encoder converts the audio, video and data signals into the digital format and the multiplexer mixes these signals. DTH receiver receives frequencies in the range of 10.7-12.75 GHz from the satellite and down converts in the range 950MHz-2150MHz. The tuner for viewing selects the required RF channel. The users will require a small dish antenna and TV setup boxes to decode channels and view numerous channels. DTH boxes (decoders) are of addressable type. Each individual box can be linked/delinked from the DTH control centre. A subscriber can make a choice from the set of channels. DTH offers better quality picture than conventional cable TV because cable TV in India is analog. In spite of the digital transmission and reception, the cable transmission is still analog. DTH offers stereophonic sound effects, which is not the case with Indian cable TV market. DTH can reach those remote areas where Doordarshan and cable TV have failed to penetrate. The government has allowed DTH to be used for voice, data, fax, Internet with the binding that for each value added service, a separate licence would required to be taken by the DTH company. It can become a prominent source of high-speed Internet delivery to the subscriber’s home. The DTH venture will be a 100-channel platform to start with and the initial one time cost, which the subscriber shall have to pay, will be in the range of Rs 5000. This will include the DTH STB and the dish antenna. The introductory offer may have the monthly subscription of Rs 150. STB will perform its functions through a smart card activated through a Subscriber Management System (SMS) managed wirelessly by the service provider. A programme menu will enable the user to choose from various channels and packages on offer. DTH is an alternative to CAS (Conditional Access System) cable TV service. The fact is that both DTH and CAS have co-existed worldwide and grown technically and commercially. CAS is delivered through cable and DTH is wireless enabled through satellite. DTH setup box (STB) is different from CAS STB and is not interchangeable. Open architecture of DTH STB enables the subscriber to shift platforms without altering the hardware. DTH service quality is affected by rain and humid conditions and researchers are working to remove this drawback. The government has laid a stringent code of conduct for the DTH broadcasters. The owners of DTH companies will have to be Indian residents. The earth station will have to be set on the Indian soil. The programme content will be strictly monitored so that it adheres to the national security and culture. DTH, as a technology is all set to play a pivotal role in 4G convergence. The ways of nature are very strange. The emergence of cable TV had made the VCR industry redundant and now the day is not far when the DTH TV shall take over the baton from the hands of cable operators. Ultimately it is the viewer who is bound to gain. The writer is Asst. Professor, Dept. of Electronics, Punjab Engineering College |
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Building tips TAKE extra care in fixing the plinth or floor level of the house. Keep the centre level of the road running in front of the house in view. Keep its future raisings in view. There is a general tendency to keep the level too high to avoid entry of rain water in the house. Too high level results in a steeper ramp at the entrance gate causing a permanent problem for the vehicles entering the house. Otherwise the government land has to be encroached upon to keep a gentle slope which may invite trouble. A floor level 12 inch to 15 inch higher than the centre level of the road should be considered sufficient. ** When the foundations of the house have been filled up to DPC level, perform an important check before laying the DPC. Check both diagonals of each and every rectangular room. These should be equal. If both diagonals of a room are not equal that means its walls are not at right angles to one another. Ask the mason to find out the error and correct it. This is the only stage when this correction can be carried out. Otherwise you may be creating a skewed room for you to live in forever. When a diagonal cannot be measured due to some obstruction like a column, check each corner angle to be 90 degrees by simple triangulation method. ** Always use an aluminium strip at the junction of floor of the house with that of kitchen, bathrooms and the verandahs. Use a 16 gauge or thicker strip. A glass strip if provided at these junctions may soon get broken and may hurt naked feet. Keep the floor levels of the kitchen, all bathrooms and all verandahs half inch down than the level of floor in rooms. This will avoid flow of water into the rooms. See that the doors to kitchen and bathrooms are so provided that these strike against the strip when in closed position. ** It is common occurrence that the cement mortar used for brick masonry or plaster work is mixed by the masons in the morning and then the labour keeps supplying it to the masons sitting over the scaffolds. This is a most dangerous type of working. Cement loses most of its power by the time it is used and provides no bond or strength to the building. Cement has an initial setting time of just half an hour, so always take care that only that much mortar is prepared at one time which can be consumed within half an hour. Mortar should therefore be prepared every half hour to have best results. ** Always embed sanitary pipes in the wall foundations before laying of Damp Proof Course (DPC). Always erect rain water pipes in position after laying of DPC. Never mix up the sanitary pipes and rain water pipes. Visibly, these look alike, that's why these need to be stacked separately. Both, the sanitary pipes and rain water pipes are made of Cast Iron (CI) and are black painted but sanitary pipes are heavier in weight than rain water pipes. So take care and make right use. ** While laying the working shelf in the kitchen, try deciding the position of gas burner and keep a one inch dia hole in the shelf at a suitable location for the gas pipe to pass. This will avoid taking the odd looking pipe up from the front and will save it from damage also. |
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NEW PRODUCTS
& DISCOVERIES
AN as-yet-unnamed species of snail living around hydrothermal vents deep beneath the Indian Ocean bears an unusual suit of armor forged from the dissolved minerals spewing into its seafloor habitat. The sides of the snail’s foot are covered with scales that range up to 8 millimeters in length and overlap like roof tiles, says Anders Warén, a marine biologist at the Swedish Museum of Natural History in Stockholm. The core of those structures is made of a protein called conchiolin, a common component of many mollusk shells. What makes these flaps unique is their 100-micrometer-thick coating of iron sulfide, a biological armour that’s made of mineral particles just 1 µm in diameter. Bacteria living on the surfaces of the scales may contribute to the formation of the mineral particles there. However, because the tiny iron sulfide spheres also show up throughout the conchiolin core of each scale, the snail itself probably controls the overall growth and placement of the particles, says Warén. As snails are wont to do, these sulfide-armoured creatures live sedentary lives. This species doesn’t even bother to eat. Instead, the animals gain energy from symbiotic bacteria that live within the cells of a gland in their esophagus, says Warén. Most mollusks have such tissue, but in this armored species, the gland is about 100 times the size of that found in related species. The bacteria harboured in the gland oxidise dissolved sulfides that are absorbed through the snail’s gills, says Shana K. Goffredi, a marine biologist at the Monterey Bay Aquarium Research Institute in Moss Landing, Calif. She, Warén, and their colleagues describe the armoured snail in the Nov. 7 Science.
Laser-sensitive dyes Working with capsules of dye just a few billionths of a metre in diameter, researchers at University of Toronto and the advanced optical microscopy facility at Toronto’s Princess Margaret Hospital have created a new strategy for encrypting photographs, signatures and fingerprints on security documents. “This technology will give security or customs authorities the confidence that documents are not fake,” says U of T chemistry professor Eugenia Kumacheva, who holds the Canada Research Chair in Advanced Polymer Materials. “It gives a very high level of data encryption and is relatively cheap to produce.” A thin film of polymer material is produced from tiny three-layer capsules comprising three different dyes, Kumacheva explains. Each layer is sensitive to light at a particular wavelength - ultraviolet, visible or infrared. Using high-intensity irradiation, Kumacheva uses differing wavelengths to encrypt several different patterns onto a security document. To the naked eye, the identification document (a passport or smart card, for example) might reveal a photograph, but under other detection devices could reveal signatures or fingerprints. |
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UNDERSTANDING THE UNIVERSE Sun looks big during the morning and the evening. Why? One can measure the size of the sun by using a simple survey instrument like a theodolite or, more simply, by using a transparent scale at arm’s length-you should be careful to use appropriate solar filter while looking at the sun (you cannot and should not look at the sun without appropriate protection, especially when it is high up in the sky) You will find that there is no difference in the measured size of the sun while it goes from sunrise to a high position in the sky! The difference we all observe is entirely psychological! The reason for this has been discussed extensively. Two of the explanations given are the following. 1). When we look at the sun near the horizon we also happen to see trees, people and buildings at the same time. Many of these are far away and look very small. But our brain knows that in actual fact they are much bigger. Therefore it automatically makes a correction in the observed size of the sun and makes us perceive it as bigger. I am not entirely happy with this explanation. Why only so much bigger? Incidentally, the same observation is made in respect of the rising or setting moon and the very same explanation is given. Some day I would like to see the sun high up with a number of airplanes in the same field of view. I wonder if the sun would start looking bigger. If some of you have a chance to make this observation please share it with me. 2). There is yet another explanation that has been offered. We all have sensation that our sky is like dome. One could argue about the way this feeling came about but there is no question that we have that impression. In a dome the ceiling is never as far as its diameter. That is our experience of all the domes we have ever built. Therefore our brain places the moon or the sun near the horizon at a grater distance than when it is high up in the sky. It makes a correction for this difference and makes the moon or the sun look bigger near the horizon. I have given you the explanations I am aware of. One thing one can definitely say — that there is no physical difference in size. It is only psychological. There is a long way to go before our brain really understands itself. How does a microphone or a telephone mouthpiece absorb the sound? Inside the microphone or a telephone mouthpiece there is a transducer that can convert the pressure changes of a sound wave into electrical changes. Sound is nothing but a longitudinal compression wave. The frequency, or the number of compressions per second, also determines the frequency or pitch of the sound. The amplitude of compression and rarefaction depends on the volume. Transducers are of various kinds. It could be a tiny condenser where the changes in electrical capacitance due to vibration of a condenser plate are sensed. It could also be a coil mounted on a diaphragm that responds to the sound vibrations and a varying voltage in the coil is generated if it is free to move around a magnetic core. It could also be a piezoelectric crystal that produces electrical signals in response to changes in pressure. There might be still other ways of converting sound vibrations faithfully into electrical vibrations. The basic requirement is the demand for high quality conversion. The electrical vibrations can then be transmitted over landlines, radio waves or optical fibers, using analogue or digital techniques. A wind flow follows a speeding vehicle. How does this happen? When a vehicle moves it has to push out the air in front. There is a compression of air. Simultaneously new space is created behind the vehicle, where a low pressure is continuously created. The flow of air required to respond to the pressure differences created by the moving vehicle is often turbulent. It is felt along the path of the vehicle, particularly behind it where clouds of dust make the life of pedestrians miserable, particularly when the surface is not well paved. There is another effect that is noticed easily when we stand on a railway platform while a train goes past at high speed. We feel that we are being pulled towards the train. This is a real effect. The physical reason is that due to fast moving stream of air near the train a zone of low pressure is created around it which has a tendency to pull us towards the train. This is the so-called Bernoulli’s Principle operating. This is the reason we are advised not to stand very close to the edge of the platform when a fast train is expected to whiz past. Why are the flames always seen pointing upwards? A flame is produced by exothermic combination of combustible gases with oxygen. These combustible gases might come from various sources, such as the vaporised hydrocarbon of a candle, wood or coal. Combustion produces heat. The combustion products as also the air coming from the side get heated. Hot gases are lighter. Therefore they rise — we call this process convection. Rising hot gases and air mix and the process of combustion continues efficiently because sufficient quantity of oxygen is available as the gases rise. The burning of rising gases is what we call a flame. The flame extends up to a height where the combustible vapour is all burnt out. It is clear that the shape of the flame is a consequence of convection, which comes about because hot gases are lighter. The direction of the flame is opposite to the direction of the gravitational force of the earth. You would not see such directed flames in an orbiting satellite, because in that weightless situation there is no convection. |
MODERN cable television networks deliver “bouquets” of programmes, many of which are “free to air” and some are “paid”. The Government of India has recently given concurrence to the implementation of direct-to-home (DTH) television broadcasting. In this technology the high-density TV signals in the Ku band are directly beamed from the satellite to the user’s home. DTH is an encrypted transmission that travels to the consumer directly without the traditional ground infrastructure.
This observation applies equally to a rising or setting full moon. I had answered a question about that some time ago and I would repeat the answer, with appropriate modification, as follows.