Habari zenu?
Mwalimu @Meria Mata?
So many days hatujaingia darasani! So leo niko na jambo.
I realized that whenever we are talking things fta satellite TV, there are some terms that pop up more oftenly than not. I have been taking them for granted and assumed I understood everything, kumbe I was terribly mistaken!
So, Mwalimu, will you, please, begin the class by letting me know exhaustively the various types of satellite dishes? And their differences? And the advantages of one as compared to the others?
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Prime focus Dish
A Prime focus dish is a reflector whereby the waves received are concentrated on a central point in front of the dish. The prime focus is usually in the same plane as the most central point on the reflector itself It can also be viewed as a concave reflector.
http://www.techsawa.com/images/demo/prime%20focus%20reflector%20illustration.png
A prime focus dish is used to receive C band signals and is usually big in size. These type of reflectors are usually big and heavy and require a considerable amount of space to install them. Because of their big size, prime focus dishes are usually affected by wind, that is why some dishes are made of perforated metal or mesh. But you cannot receive Ku band waves with a mesh type dish, this is because the Ku band waves with their higher frequencies and shorter wavelengths will just penetrate the big holes and not be reflected at all.
Offset Dish
An offset dish just like the name suggests reflects the signals to an offset position usually around 20 degrees offset. The reflective area can be viewed as a parabola. The back of the LNB on an offset dish usually points at a false location (not the satellite aimed by the dish). The LNB and LNB arm of an offset dish does not in any way block the waves the dish is receiving unlike the LNB and LNB arms of a Prime focus dish.
http://www.techsawa.com/images/demo/offset%20reflector%20illustration.png
Offset dishes are usually small in size and are used to receive Ku band waves. Most pay TV providers usually use Ku band frequencies because it usually makes the equipment at the consumers end cheaper. There is nothing like a perforated offset dish like in the case of Prime focus reflectors. Offset dishes have an advantage that they are cheaper, lighter and can be installed almost anywhere provided there is a clear view of the sky.
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