בהרחבה על LNB:(בעבר והיום)

[איש המציאות]

LNB - Low Noise Block-downconvertor



( it converts a whole band or "block" of frequencies to a lower band).



============================



Is there actually a different LNB for prime focus dishes + offset dishes?





In the old days, LNB noise figures were high, and the gain (amplification) was low

So, an LNB and feedhorn had to be matched to the dish. The internal antenna of the LNB had to be at the exact focal point of the dish and the horn had to be flared in such a way that, with the LNB at the focal point, the horn could "see" the exact circular area of the dish - no more and no less. If it was less then it wasn't collecting signal from the full area of the dish. If it was more, it was also collecting unwanted "noise" from any warm object (wall) or from the sky behind the dish.





Nowadays, satellite transponders can produce typically 50 or 60 Watts and LNBs have higher gain and lower noise figures. With these strong transmissions, you can get away with murder. People stick any old thing on the end of the boom arm - which rather explains why one man's 0.6dB LNB is another man's nightmare when the signal strength is not optimum!

It's very important that the LNB matches the dish exactly. This is one good reason why the dish comes with its own LNB.



The manufacturers might "fudge" the issue if asked. After all, if they admit that their LNB works best with, say, an 80cm Lenson Heath dish and you just bought an 1 metre dish made by someone else, you might not be too happy.





As a general rule, any standard LNB will work with a circular (prime focus) dish or an offset focus dish which is taller than it is wide (which "looks" circular when viewed by the LNB).



However, a dish which is wider than it is tall will need a special LNB.