Nicam Processing; Audio Signals From The Interface; Am Audio Signals At L Standard - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set
quencies of 5.5 /5.74 MHz or even other
sound transmission standards. These two IF
channels can be programmed by the operat-
ing software to different sound carrier fre-
quencies. For the digitally filtered sound/IF
carrier full modulation is carried out in both
channels. The digital sound signals are felt on
the output of the demodulator/decoder block.
In the second sound/IF channel decoding of
the pilot sound carrier takes place with sound
transmission by the two carrier frequencies
5.5 /5.74 MHz. In addition to the FM modu-
lated VF signal, the 5.74 MHz carrier is modu-
lated with an AM modulated 54,7 kHz pilot
sound carrier. The pilot sound carrier is vari-
ously modulated depending on the transmitted
VF signals (mono, stereo or two-tone).
Modulation type from pilot sound carrier
Operating type
Mono
Stereo
Two tone
Detection of the pilot sound carrier is carried
out in the second IF channel, in which the
5.74 MHz sound carrier processing takes
place, The result of the continuous pilot sound
carrier evaluation is written to the "Stereo De-
tection Register" of the MSP. This register is
read cyclically by the CCU via the I²C bus,
and depending on the operating mode set the
CCU communicates to the MSP via the I²C
bus the type of de-matricising that must be
switched on.
5.2.3

Nicam processing

Nicam is a sound transmission system de-
signed for terrestrial transmission. It was de-
veloped in the United Kingdom for stereo TV
transmission and is now used in a number of
other European countries.
Document Q 2500
Natural frequency
unmodulated
117.5 Hz
274.1 Hz
The name "Nicam" is an abbreviation and
stands for
pounded audio multiplex".
In this system the digital audio information is
modulated by an additional sound carrier.
The signal gets its name QPSK signal from
"Quadrature phase shift keying" from the type
of modulation, which is quadrature modulation
with rotating phase,
Owing to the various television standards two
different sound carrier frequencies are used
for the Nicam transmission. For PAL-I the
sound carrier is 6.552 MHz and for PAL-B/G it
is 5.85 MHz.

5.2.4 Audio signals from the interface

switching
If audio signals are fed to the Scart sockets,
the selected VF signal pair is applied directly
to pins 53/54 of the multi-standard sound
processor via the audio interface switch (see
Audio Signal Path). If the signal board is fitted
with 3 AV sockets the audio signal is output by
the AV3 socket directly to pins 56/57 of the
MSP. The audio signal passes via an internal
switch to two ADCs. The audio signal is digi-
tised by the two ADCs for further processing
and then led internally to the audio base band
processor.

5.2.5 AM audio signals at L standard

If AM signals are processed in the device, the
IF preparation and demodulation is carried out
in the HF/IF block.
The VF signal comes from pin 23 of the cable
tuner to pin 60 of the MSP 3411. Furthermore,
the signal path is the same as the signals that
come from the interface transfer to pins 53, 54
of the MSP.
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