L2101 &L2102 Integrated Receiver Decoder Instruction Manual – Issue 1 – September 2003
Page
124 of 126
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Appendix B. Appendix B: LNB Theory
Of Operation
B.1
Why is an LNB needed?
A signal from a satellite is a very low power signal. The satellite reception dish
does a first amplification by reflecting and concentrating the signal received into
one focus point. The LNB, mounted exactly at this point in front of the parabolic
dish, further amplifies this signal because it is still very weak. This amplified
satellite signal cannot be sent directly though a coax cable. Due to the still very
high frequency (10 to 13Ghz) sending this signal directly into a coax cable would
result in very high signal loss.
This is why the LNB also converts the signal into a lower frequency. The LNB
Frequency determines over how many Mhz the signal is converted downwards.
B.2
Example:
11929: Mhz Satellite frequency:
-10750: Mhz LNB frequency:
=1179: Mhz Signal frequency to IRD
The signal that is sent from the LNB to the IRD device has to be within the IRD
input frequency range (0.950Ghz to 2.150Ghz, or 950Mhz to 2150Mhz). The
following figure shows a basic set up for satellite reception.
Figure B-6:
Basic Setup for Receiving A Satellite Signal
Satellite
Satellite dish
Scopus IRD
Frequency range of
satellite signal:
10 GHz to 13 GHz
approx.
Frequency range here is:
sattelite frequency - LNB frequency
Input Frequency Range
950 Mhz .. 2150Mhz
LNB
B.3
Frequency Calculation IRD + LNB
As demonstrated in the previous example, the LNB determines the actual
reception frequency range. The reception frequency range of the IRD and LNB
together is calculated as shown in the next example:
LNB
frequency:
=
10750
Mhz.
Input frequency range:
= (950 + 10750) (2150 + 10750) Mhz
= 11700 Mhz ..12900 Mhz
