Technology of Q 2500 colour TV set

Technology of Q 2500 colour TV setquencies of 5.5 /5.74 MHz or even othersound transmission standards. These two IFchannels can be programmed by the operatingsoftware to different sound carrier frequencies.For the digitally filtered sound/IFcarrier full modulation is carried out in bothchannels. The digital sound signals are felt onthe output of the demodulator/decoder block.In the second sound/IF channel decoding ofthe pilot sound carrier takes place with soundtransmission by the two carrier frequencies5.5 /5.74 MHz. In addition to the FM modulatedVF signal, the 5.74 MHz carrier is modulatedwith an AM modulated 54,7 kHz pilotsound carrier. The pilot sound carrier is variouslymodulated depending on the transmittedVF signals (mono, stereo or two-tone).The name "Nicam" is an abbreviation andstands for "Near instantaneously compoundedaudio multiplex".In this system the digital audio information ismodulated by an additional sound carrier.The signal gets its name QPSK signal from"Quadrature phase shift keying" from the typeof modulation, which is quadrature modulationwith rotating phase,Owing to the various television standards twodifferent sound carrier frequencies are usedfor the Nicam transmission. For PAL-I thesound carrier is 6.552 MHz and for PAL-B/G itis 5.85 MHz.5.2.4 Audio signals from the interfaceswitchingModulation type from pilot sound carrierOperating typeMonoStereoTwo toneNatural frequencyunmodulated117.5 Hz274.1 HzDetection of the pilot sound carrier is carriedout in the second IF channel, in which the5.74 MHz sound carrier processing takesplace, The result of the continuous pilot soundcarrier evaluation is written to the "Stereo DetectionRegister" of the MSP. This register isread cyclically by the CCU via the I²C bus,and depending on the operating mode set theCCU communicates to the MSP via the I²Cbus the type of de-matricising that must beswitched on.5.2.3 Nicam processingNicam is a sound transmission system designedfor terrestrial transmission. It was developedin the United Kingdom for stereo TVtransmission and is now used in a number ofother European countries.If audio signals are fed to the Scart sockets,the selected VF signal pair is applied directlyto pins 53/54 of the multi-standard soundprocessor via the audio interface switch (seeAudio Signal Path). If the signal board is fittedwith 3 AV sockets the audio signal is output bythe AV3 socket directly to pins 56/57 of theMSP. The audio signal passes via an internalswitch to two ADCs. The audio signal is digitisedby the two ADCs for further processingand then led internally to the audio base bandprocessor.5.2.5 AM audio signals at L standardIf AM signals are processed in the device, theIF preparation and demodulation is carried outin the HF/IF block.The VF signal comes from pin 23 of the cabletuner to pin 60 of the MSP 3411. Furthermore,the signal path is the same as the signals thatcome from the interface transfer to pins 53, 54of the MSP.Document Q 2500 114 © Loewe ProCollege