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| Thread ID: 98056 | 2009-03-09 23:13:00 | Satellite dish question | prefect (6291) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 755088 | 2009-03-09 23:13:00 | How do those satellite dishes work that seem to made from mesh material. I thought the signal came from space hit the dish and ricocheted into the lnb or what ever its called. Hard to see how signal would bounce from mesh. To be honest I haven't seen them up close only from the road and my sight is a bit buggered. |
prefect (6291) | ||
| 755089 | 2009-03-10 00:35:00 | From my understanding it is the size of the mesh that matters. If to big the signal well pass right through it, but if it is the right it won't and well reflect back to the receiver. They are made like that to save on weight. :) |
Trev (427) | ||
| 755090 | 2009-03-11 09:20:00 | It is (roughly) the smoothness of the dish surface relative to the wavelength of the signal that counts. At the frequencies of old style TV, a simple rod makes a pretty good reflector. At higher microwave frequencies, it needs to be fairly smooth. When you go into light waves (same sort of stuff, give or take a few photons) it has to be very smooth indeed. A wrinkly mirror is not too useful, and (depending on the mesh size) a mesh reflector drops off in efficiency as the frequency goes higher, but it will work fine at lower frequencies with their longer wavelength. The newer satellites use much higher frequencies than the first generation ones, so a mesh reflector may be a bit of a disappointment. A basketball will bounce off wire netting, a slug pellet is likely to pass through most times. |
R2x1 (4628) | ||
| 755091 | 2009-03-11 11:31:00 | Prefect, Yes, the signal is reflected to and gathered by the LNB -Low Noise Block- which is an RF amplifier and Frequency Changer, powered by low Voltage through the connecting lead from the receiver unit. The supplied Voltage changes from about 12V to 17V, depending on the polarity of the selected channels which are alternatively polarised for good channel separation. The critical properties of the dish are the curvature and diameter which need to suit the wavelength of the received signals. The alignment is also extremely critical. A few millimeters out at ground level, horrizontally or vertically would mean a long way out at satellite altitude. I've read about a few people making up their own dish assembly with a dustbin lid but this is not recommended. |
blanco (11336) | ||
| 755092 | 2009-03-11 19:18:00 | If the finish is so important why are they powder coated instead of a gloss paint. I have a mini sat dish(40 CM) that I use on my camper when I go away and on my house when I am at home . The signal and quality are about 70% cant get any higher by fine tuning elevation, direction and twist of lnb. Thats at home and and on the road anywhere. Think the 70% is because the dish is smaller but the freeview display on tv really good better than vhf aerial ever was. I got sat finder but its just as easy to use on screen display and the kids scream out stop when quality and signal are best. |
prefect (6291) | ||
| 755093 | 2009-03-11 21:06:00 | The paint is selected to be non-reflective to the frequencies of interest. As far as the desired signal is concerned, the metal surface of the dish is the reflecting surface. The reason for the matt finish is to avoid infra-red reflection, which could turn the assembly into a solar oven and grill the LNB. (It still wouldn't taste any good.) The paint is normally grey as a compromise between black, which would reduce optical reflections somewhat, and white which would minimise temperature changes and subsequent distortion of the dish. |
R2x1 (4628) | ||
| 755094 | 2009-03-11 21:47:00 | Thanks for that squire. | prefect (6291) | ||
| 755095 | 2009-03-12 05:52:00 | Cant find teletext any where in menu. I have freeviewshop.co.nz setup. | prefect (6291) | ||
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