SERVICE MANUAL
Document No
Date of Origin
Date of REV
51-L-DSR004
98-10-21
PAGE REV.
0
PAGE
11 /102
S-00-005(96.03.27)
REV.1
4-2. Tuner
a LNB (Low Noise Block Down Converter)
converts
the incoming
satellite
signal from 12GHz down to an intermediate
frequency
(IF) of 1 GHz to 2 GHz.
Then a PLL frequency
synthesizer
further
down converts
the signal to a
second IF (479.5MHz).
The DEMUX (with microprocessor)
adjusts
the frequency
delivered
by this
circuit
in such a way that the IF signal falls within the bandwidth
of the
IF surface
acoustic
wave (SAW) filter.
The I/Q down converter
translates
the IF signal to baseband.
TUNER
LNB
DiSEqC 22KHz Block
QPSK Demodulator
DEMUX (ST20TP2)
I
Q
Figure 4.2 QPSK Block Diagram