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Appendix C – LNB Type Description
There are several bands used for satellite transmission in use worldwide. In Europe,
Ku band is predominantly used with some C band usage. In the US, C band, Ku
band and Ka are used. The Ku band in US is divided into DBS (Direct Broadcast
Satellite) and FSS (Fixed Satellite Service) bands. The satellite transmission bands
are:
Europe Ku band: 10.7 GHz – 12.75GHz
US C band: 3GHz – 4.5GHz
US DBS band: 12.2GHz – 12.7GHz
US FSS 11.7Ghz – 12.2GHz
US Ka: 18.3GHz – 18.8GHz and 19.7GHz – 20.2GHz
Because the losses in coax are quite high for these frequencies, the satellite signal is
first downconverted to a more manageable 950 MHz to 2150 MHz by the LNB for
transmission from the dish to the receiver. This is called the IF (intermediate
frequency) or also the L Band. The legacy LNB types do a straight conversion using
a LO (local oscillator) which is mixed with the incoming signal. This gives a sum and
a difference frequency. Where the LO frequency is below the incoming frequency,
this results in: Freq
satellite
– Freq
LO
= Freq
receiver
This is the normal case. In C Band,
however, the LO frequency is above the incoming frequency so: Freq
LO
– Freq
satellite
=
Freq
receiver
Satellite signals are transmitted as polarized waves so that the spectrum can be used
to maximum advantage. Signals can have Vertical, Horizontal, Right circular or Left
circular polarisation. Most LNBs can switch between V/H or R/L using voltage
switching of 13V or 18V. The conventions are:
13V = V or R
18V = H or L
The legacy LNBs supported are:
9.75, 10.0. 10.05, 10.6, 10.7, 10.75, 11.0, 11.2, 11.25, 11.3, 11.475
There are two C band LNBs. The C band standard is 5.15GHz, but 5.95Ghz is also
used. Normal polarisation switching is used: 13V = V or R, 18V=H or L
The “IF” LNB is “pass thru” – No conversion is performed.
It is important to remember that after the LNB does the conversion, the frequency
passed into the meter is in the range 950MHZ to 2150MHz. The LNB setting in the
instrument is used only to make the calculation from Satellite frequency and then
tune the instrument.
Summary of Contents for satlook Lite
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