Operating instructions

DVB3030/DVB3030L Digital Video Broadcast Modulator Operation
TM052 - Rev. 3.5 3-1
Section 3 – Operation
3.0 Theory of Operation
A digital terrestrial interface supplies the modulator with a data stream. The data stream is
synchronized if the incoming stream is framed. The data is scrambled, and FEC is added. The
data is then convolutionally encoded, punctured, then constellation mapped. The resulting I&Q
symbols are digitally filtered. The data is then converted into an analog waveform and is vector
modulated onto an RF Carrier produced from the Transmit IF Synthesizer Circuitry.
3.1 DVB3030 Operation
A block diagram of the signal flow is shown in Figure 3-1 below.
Figure 3-1. Functional Block Diagram
3.2 Last Rate Control
The mechanism used to set the Symbol Rate (SR) and Data Rate (DR) in the modems has
traditionally allowed SR to have precedence. This means that if the Modulation Format (MF),
Framing Rate (FR), or Code Rate (CR) are changed, then the SR is assumed correct, and the
DR is recalculated. Several problems have become apparent, some code related, some operator
related:
1. The operator does not have the privilege of having DR to have precedence over SR.
This may be important for DR dependant applications, such as fixed rate interfaces or
fixed rate data multiplexers. In some cases, the iterative procedure to set an exact DR
when no calculator is available becomes very a tedious, time consuming iterative
process.
2. The block commands for Ethernet or remote port operation have had problems because
the SR, DR, and other rate modifying commands can all be received simultaneously.
This has caused problems with precedence and ordering of calculations, and in the
timing of the multiple commands in relation to modem re-synchronization. The result
being some commands not being executed properly.
With Last Rate Control, a front panel setting allows the operator to select between Symbol, Data
and Auto modes. A status submenu under Monitor allows the operator to check the current
modem setting.