SMD 989
– User Manual
Page 36 (105)
Configure Modulator
– Modulation Parameters
The
Modulation
tab provides setup settings of the modulation parameters. First, choose the
Modulation/FEC code to use and then select how you wish to set the output symbol rate. You
may enter the desired output symbol rate or input bit rate or have the internal calculator
recommend a setting. The following section describes entry of these parameters.
The
Enter Rate By
field provides the user a choice of how to setup the output Symbol Rate or
Max Bitrate entry fields. The values in these fields are mathematically related depending on the
modulation mode, modulation type, and FEC settings. The SDM 989 contains an internal symbol
rate or max. input bitrate calculator to assist.
Enter Rate By
-
Output Symbol Rate
-
Input Bitrate
Description:
Output Symbol Rate mode allows the entry of the desired output symbol rate. The
SMD 989 calculates the maximum input bit rate and lists it in the Max. Bitrate field.
Description: Input Bit Rate mode allows the entry of a known input bit rate. The SMD 989 then
calculates the needed symbol rate and lists it in the Symbol Rate field.
With output Symbol Rate you enter the desired output symbol rate. It must be mathematically
proper based upon the input bit rate measured by the system. When a higher than needed
symbol rate is entered, the modulator inserts null packets to achieve the rate. When entering a
lower than needed symbol rate the SMD 989 removes nulls, if they exist, from the stream.
With Input Bitrate, the SMD 989 uses the entered bitrate along with the modulation settings to
calculate the needed symbol rate. If it is known that the input transport stream contains a
significant amount of null packets it is possible to enter a bitrate that is lower than the actual input
transport stream bitrate. In this case the SMD 989 will remove existing nulls.
Important Note: When entering a bitrate lower than the input bitrate or a symbol rate below
the minimum, there must be enough nulls in the input transport stream to be removed to
allow the lower bitrate or symbol rate or errors in the transmission transport stream result.
The SMD 989 contains a symbol rate or input bit rate calculator to assist with these selections. By
clicking the
icon, the recommended symbol rate will be inserted into the Symbol Rate field
or maximum input bitrate inserted in the Bitrate field.
Figure 30: Single stream DVB-S2 Configuration
