Advantech L-Band Satellite Modulator Installation And Operation Manual Download

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Installation

BUC power is off (bucpower off)

10 MHz reference is off (tfref off)

Set modulator power to -25 dBm (tlevel -25)

If required and if the option is fitted, turn on DC power to BUC (bucpower on).

If required and if the option is fitted, turn on 10 MHz reference to the BUC (tfref on).

Increase modulator output power to desired level (tlevel < desired level >).

Note

Before attempting to bring the modulator on line, the operator should become familiar with

the operation of the modulator while off line. Refer to the manual to obtain a thorough

understanding of modulator operation using a terminal emulator (or PC with terminal

emulation program).

2.7.2

Choice of FEC

The SBM75e modulator will always support a traditional basic DVB-S (RSV) coding scheme with
BPSK and QPSK modulation – either Intelsat IESS-308/9, or DVB-S (or both). Traditionally Intelsat
systems have been used for telecommunications data (multiple 64kbps streams and T1/E1 traffic)
while DVB-S has been used for MPEG digital video broadcasting. However, DVB systems are
increasingly also being used to transmit data both in MPEG format and as raw data.

DVB FEC systems always concatenate RS and Viterbi coding whereas the Intelsat systems support
RS as an option. Operation without RS can be important when transmitting low-latency services
such as voice traffic: removing the RS decoding overhead.

With BPSK and QPSK modulation, DVB-S supports ½, 2/3, ¾, 5/6 and 7/8 inner code rates with a RS
(204,188) outer code. Intelsat supports ½, ¾ and 7/8 inner code rates with various outer RS code
rates including RS (126,112) and RS (219,201). The Intelsat system without RS codes offers a few
100 data bits of latency. With RS coding, an interleaver of depth 4 or 8 can be chosen to trade
off latency and performance. The DVB system has approximately 32kbits of latency (code-rate
dependent).

The modulator can transmit RS-530 or HSSI data using either DVB-S or Intelsat. DVB systems out-
perform (by approximately 1dB) Intelsat systems because they include a better interleaver
between the constituent Viterbi and RS codes.

The SBM75e modulator also supports higher order modulation systems, such as 8PSK and 16QAM.
These systems are typically used when the link budget permits since, in combination with
appropriate FEC, they permit higher spectral efficiency and hence reduce the required satellite
bandwidth.

8PSK modulation is currently more popular than 16QAM as it does not require high-linearity
amplifiers and transponders. The AMT-70 modulator can be enabled to support IESS-310 8PSK
systems (a PTCM 2/3 code, with an RS (219,201) outer code) giving about 2 bits/s/Hz. It can also
support DVB-DSNG (PTCM 2/3, 5/6 and 8/9 rates, with the RS (204,188) code) and eTPC rates
0.75,0.79, 0.87 and 0.92. Turbo modes are about 1dB better than the roughly equivalent DVB-
DSNG systems. The Intelsat system is about 1.5dB inferior to the DVB system, due to differences in
the interleaving structure.

The SBM75e modulator also supports 16QAM in two coding modes: DVB-DSNG and eTPC. DVB-
DSNG 16QAM supports ¾ and 7/8 rates with the RS (204,188) outer code. 16QAM with eTPC can
usefully operate in 4 rates: 0.75, 0.78, 0.87 and 0.92.

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SBD75e Series Modulator Installation and Operation Manual