Linear and Circular Polarization....

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sanjay kumar
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Linear and Circular Polarization....

Post by sanjay kumar »

Both C band and Ku band satellite signals are broadcast using two polarization methods, namely, Linear and Circular polarization.

We won’t get into the specific physics of the two methods of broadcasting radio waves, but it is worth mentioning that circular polarity signals are most often used when signals are primarily broadcast into countries close to the equator because they are more immune to solar radiation interference.

The majority of satellites over the Americas broadcast using linear polarization, but there are a few exceptions with Atlantic C band satellites and DTH Ku band satellties:

Circular Polarization Satellites (C Band)
8W
11W
18W
20W
22W
24.5W
27.5W
34.5W
40.5W
47W
53W

Circular Polarization Satellites (Ku Band)
Dish USA (61.5W, 72.7W, 77W, 110W, 119W, 129W)
Dish Mexico (77W)
DirecTV USA (95W, 99W, 101W, 103W, 110W, 119W)
DirecTV Mexico (95W)
Bell Satellite (82W and 91W)
circular_to_linear_conversion.JPG
circular_to_linear_conversion.JPG (48.07 KiB) Viewed 930 times
If you want to receive any of the satellite signals above, you need to insert a dielectric plate into the throat of your LNBF. The plate should make a 45 degree angle with both probes inside the LNBF. It will convert circular signals into linear signals but will add some attenuation to the signal. Furthermore, your LNBF will no longer receive linear signals. Perhaps a better option would be to purchase a circular only LNBF to avoid any attenuation, but unfortunately, such prime focus LNBFs are not manufactured for either C or Ku band!
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