Audio Baseband Processing; Demodulator/Decoder Block - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set

5.2.1 Audio baseband processing

− Flexible selection of the sound source to be
processed, e.g. demodulator or Scart
socket
− Selectable de-emphasis
− Stereo matrix

Demodulator/Decoder block

Intercarrier-
signal from
tuner
IF signal
from SAT tuner
5.2.2 Demodulator/decoder block
The sound/IF inter-carrier signal output by the
tuner passes via a band-pass consisting of
L/C 2032, R/C 2033 and C 2036, to the
sound/IF input1, pin 67 of MSP 3411. The
band-pass suppresses frequency components
below 4.5 MHz and above 10 MHz. In this way
sound interference that could be caused by
the colour carrier or the neighbouring picture
carrier is prevented. If the Twin-SAT unit is
used a SAT sound/IF reaches the sound/IF
input2 on pin 69 of MSP via pin connector W
1416 /pin 4 and the band-pass, consisting of
L/C 2037, R/C 2038 and C 2009.
The analogue sound/IF signal is passed inter-
nally from pin 67 (Hyperband tuner) or 69
Document Q 2500
IF channel 2
IF1
AGC A / D
IF2
IF channel 1
− Pre-amplifier for Nicam/FM and Scart sig-
nal
− Independent volume adjustment for loud-
speaker and headphones
− Adjustment
stereoscopic sound and balance in the
loudspeaker branch and virtual surround
QPSK
Decoder
Oscillator
mixer
Filter
Demodulator
Stereo
Zweiton
Detection
Oszillator
Mischer
Filter
Demodulator
(SAT unit) to a transfer switch that is able to
switch between the two IF inputs of the MSP
under software control. The analogue IF sig-
nal is then adapted optimally by an automatic
amplifier control, which can control input sig-
nals from 0.14 to 3 Vss, to the ADC. The ADC
changes the sound/IF signal into an 8-bit data
stream. The sampling rate is 18.432 MHz.
This is produced by the internal clock genera-
tor. The frequency determining 18.432 MHz
quartz is connected to pins 71/72 of MSP
3411. This 18.432 MHz clock is also used for
all digital processes in the MSP.
The digital sound/IF signal is now processed
in a multi-standard sound processor by two
independently operating sound/IF channels.
This is necessary, for example, in order to
process stereo transmissions with carrier fre-
113
of bass, level,
Nicam / A
Nicam
Nicam / B
Decoder
FM 2
Stereo
Detection
Register
FM 1
© Loewe ProCollege
loudness,