User manual

Section 7: System Description 7-5
Moseley SL9003Q 602-12016 Revision G
The digital audio data (linear or compressed) and the auxiliary data channel are subsequently
coded into a single data stream. In a 2 channel system, this data stream is sent to the QAM
Modulator module directly.
7.6.2. Intelligent Multiplexer
The MUX is documented in a separate user manual. Typical broadcast applications are
described here:
4-Port Mux:
For composite STL systems, the 4-port mux (with composite option card) is used to route and
multiplex the composite signal to the QAM modulator.
6-Port Mux:
For discrete STL systems, the 6-port mux (with Ethernet option card) is primarily used to
interface and multiplex an Ethernet data stream for transmission as a data channel.
7.6.3. QAM Modulator/IF Upconverter Daughter Card
BPF
70 MHz
BPF
6.4 MHz
IF Output
70 MHz
-10 dBm
PLL
Loop
Filter
VCO
76.4 MHz PLL
Data
Clk
Enbl
Ref
IF Input
6.4 MHz
-20 dBm
Synth Level
Synth
Lock
Exci ter
Level
Figure 7-3 IF Upconverter Daughter Card Block Diagram
The QAM (Quadrature Amplitude Modulation) Modulator accepts the aggregate data stream via
the backplane. The module performs up to 256 QAM modulation at a carrier frequency of 6.4
MHz, adding FEC (Forward Error Correction) bits while interleaving the blocks of data. The
result is a very spectrally efficient, yet robust linear modulation scheme. This process requires
an ultra-stable master clock provided by an OCXO (oven controlled crystal oscillator) that is
accurate to within 0.1 ppm.