Fine adjustment of Lnbs


clarke belt

Since Sirius at 5degs east recently became of interest due to the ability to watch channels there,lots of people have been looking for ways to improve their systems after finding some of the channels quite weak and some not receivable at all.

The obvious way to achieve this is to buy a larger dish but that creates all kinds of problems not the least the cost.
At one time not too long ago virtually all motorised systems used a seperate Lnb and feedhorn and the receivers were equiped with polarisers terminals and its not until you have seen the difference that a fine adjustment to skew can make on a weak signal that you realise the popular voltage controlled H/V system that most of us use now is not the best and was basically just intended for strong Astra reception.

The reason why a polarisation offset occurs is quite complex and beyond the scope of this post, but it is sufficient to say it is a factor and something can be done about it.

I had a browse through What Sat mag to see how many of the new digital receivers have incremental polariser control and was suprised to find quite a lot,but I suspect a large number of them are not being used.

Its much better to use receiver programmable per channel skew values and present systems use a non moveable ferrite polariser which fits beteen the feedhorn and the Lnb, this does introduce a small insertion loss but the reliability of the settings and the menu controlled fine settings makes it a must for situations like Sirius,and as a DXer I'v used it for a long time with very weak signals which on a standard system would remain weak and nothing more to be done to improve them.

clarke belt.