SMD 989
– User Manual
Page 77 (105)
BAY 1: MODULATOR MODULATION ↕
>ALPHA FILTER ROLLOFF: 0.35
CLEAN CARRIER ONLY: DISABLED
RATE ADAPTATION: ENABLED
PL SCRAMBLING CODE: 000000
PRBS: DISABLED
Note:
When the SMD 920 L-Band option is installed, the default spectral inversion is inverted as
the upconverter is set to invert. Setting the output to Inverted will give a normal output from the
upconverter.
This
is
shown
in
the
RF
Output
status
for
Spectral
Inversion.
Alpha Filter Rolloff
-
0.35
-
0.25
-
0.20
-
0.15
-
0.10
-
0.05
Description:
The filter rolloff is known as the Alpha coefficient (α). The smaller the α, the less
bandwidth will be required on the satellite. Rolloff in DVB-S limited to 0.35, 0.25 and 0.20.
Clean Carrier Only (Disabled/
Enabled
)
Description:
When set to Enabled the modulator outputs only a cw carrier for testing purposes.
Rate Adaptation
(Disabled/
Enabled
) Only available in DVB-S2 or DVB-S2X single mode)
Description:
When enabled a rate adaption is applied. When disabled the rate adaptatiois not
active. Rate adaptation adds or removes null packets and re-stamps PCRs in order to match TS
bitrate to the modulation payload rate.
PL Scrambling Code
(6 digit value entry)
Description:
This is used to specify a randomized scrambling sequence applied to each
PL frame and initiated at the end of each PL header. Scrambling randomizes band energy
dispersion and allows for a “signature” when may provide association to a satellite operator or
satellite. The complex code relates to an “n” value defined by an entry of
0 to 262 141.
PRBS (
Enabled/
Disabled)
Description:
When Enabled the PRBS replaces the normal input modulation feeding the
modulator with a PN23 normal or inverted BERT test signal. Select Disabled for normal output
applications.
IMPORTANT: For normal or non-testing applications in which the input is to be used to
modulate the satellite IF or L-Band carrier output, the PRBS test signal must be set to
DISABLED.
