Promax HD Ranger +, Руководство пользователя

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December 2014
17
Figure A2.4.
The LNB (Low Noise Block-converter) is an active device fruit of the great
evolution of RF circuit manufacturing and includes amplifiers, oscillators and
frequency converters in a small low cost package. The first section is made of a
device called
polarisation shifter that receives one polarisation or the other
depending on the supply voltage given to the LNB. This voltage is necessary to
supply the active devices inside the LNB.
Signals broadcast from the satellites use two polarisations simultaneously. These
can be LINEAR VERTICAL/HORIZONTAL or CIRCULAR LEFT/RIGHT depending on
the type of transmitting antenna used in the satellite. The transponder
frequencies for each polarisation are carefully selected to avoid interference to
the other polarisation commonly referred to as the crossed polarisation. In
general they are imbricate or in other words frequencies used in one polarisation
are free in the crossed polarisation and viceversa.
13 VDC VERTICAL CIRCULAR RIGHT
18 VDC HORIZONTAL CIRCULAR LEFT
Modern universal LNB's use mostly linear polarisation and have also the
capability to select a different input frequency range depending on a control
signal called 22 kHz switching tone which is overlapped with the supply voltage.
SUPPLY VOLTAGE POLARISATION BAND
13 VDC
18 VDC
13 VDC + 22 kHz
18 VDC + 22 kHz
VERTICAL
HORIZONTAL
VERTICAL
HORIZONTAL
LOW
LOW
HIGH
HIGH
In other words our LNB will output a different set of satellite transponders
depending on which supply voltage we use.