05 The Low Noise Blockconvertor (LNB)
Description
This article is from the Satellite TV FAQ, by Gary Bourgois flash@lopez.marquette.mi.us with numerous contributions by others.
05 The Low Noise Blockconvertor (LNB)
This is the Little gizmo that amplifies the very weak signals from
the dish, and also converts them to a more suitable band of
frequencies. LNB means LOW NOISE BLOCKCONVERTOR. Older systems
consisted of separate components: LNA (Low Noise Amplifier) and a
downconvertor which changed the received signals (3-4 GHz, or
GIGAherz ....A GIGAHerz is one thousand megaHz....) to 70 Mhz.
The "standard block" used today is 950 to 1450 Mhz. Both C and
KU band (while they input on vastly different frequencies) output
on the 950 to 1450 Mhz block. HOWEVER there are special consider-
ations when dealing with KU (explained later)
There is also a device called an LNBF, which combines the LNB and
feedhorn into a single unit. (See below for description of feed
assembly. The LNBF device uses a simpler method for adjusting
the polarity (voltage right on the LNB cable). You can not adjust fine
skew, just H or V. This device is practical for C band only systems.
However if the LNB part goes bad, you need to replace ALL of it.
An LNBF is especially suitable for dedicated operations, such as a
smaller dish used for only one satellite. I have a 6 foot dish which
I use for Telstar 401 only, using an LNBF, and it gives excellent
service.
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