Using a Remote Unit
HE4000 Encoding System
HE4000 Remote Command Descriptions
Remote Command
Parameter
Range
Factory
Default
Description
MOD CODE_RATE
1/2, 2/3, 3/4,
5/6, 7/8
5/6
Viterbi code rate; sets the code rate for forward
error correction (FEC) of the modulated signal.
The rate selected indicates the number of error
correction bits that will be added to the data
stream. For example, if you select the 5/6 rate, for
every 5 bits that are input to the FEC encoder, the
FEC encoder outputs 6 bits.
Viterbi forward error correction increases the
transmitted symbol rate by increasing the number
of bits in the data stream.
MOD DATA_RATE
1,000,000 to
108,000,000
bps
8448000
Data rate; used to set the modulator input transport
stream data rate.
The data rate you enter is a function of the symbol
rate and the code rate.
The data rate may be entered directly by issuing a
MOD DR command or may be computed based
upon the symbol rate you enter. Specifically, the
data rate is equal to the Symbol Rate x 2 x 188/204
x V, where V = the Viterbi code rate.
MOD SPEC_INV
Inverted,
Normal
Normal
Spectrum Inversion; used to set the modulator so
that the modulated IF spectrum is inverted.
Parameters are:
● Inverted = the modulated IF spectrum is
inverted.
● Normal = the modulated IF spectrum is not
inverted.
MOD SYM_RATE
MOD SR
1000000 to
680000000
sps
-
Used to enter the modulator symbol rate. The
symbol rate is the number of symbols required to
transmit the data stream over a satellite link using
quadrature phase shift keying (QPSK). The
symbol rate is a function of the data rate and the
code rate, including any overhead. The symbol
rate may be entered directly by issuing a MOD_SR
command or will be automatically computed based
upon the entered data rate and code rate. The
symbol rate is equal to the Data Rate x 1/2 x
204/188 x 1/V, where V = the Viterbi code rate.
When the code rate is entered, the data rate
remains unchanged, however, the symbol rate is
recomputed.
If the displayed symbol rate exceeds the allowable
satellite bandwidth, the data will be corrupted
during transmission. To determine the satellite
bandwidth required to transmit the displayed
symbol rate, use the following equation:
symbol rate x 1.35 = required satellite bandwidth
(measured in Hz)
01-0951-404 Rev B
4-21
