Comtech EF Data IPSat GW1000 - Manual (Page 31)

01-0945-401 Rev. A 08/2004 21
Main Menu →
Configuration → Advanced
→ MODEM →
Demodulator
[1] EBT - Eb/No Threshold: When the
Eb/No falls below the Eb/No threshold, the
IPSat GW1000 will report a fault. Default is
0db.
[2] AO - Acquisition Offset: When the
demodulator begins its acquisition process, it
will begin its search at the Rx frequency plus
or minus the acquisition offset. For example,
if the Rx Frequency is 1200000000 Hz and
the acquisition offset is 1000 Hz, the
demodulator will begin its acquisition at
1200001000 Hz. Default is 0hz.
[3] DD - Differential Decoding: Enables
or disables differential decoding. Used to
protect from the possibility of phase
ambiguity errors. Default is on.
[4] RM - Rx Modulation Type:
Modulation type can be set to QPSK or
BPSK. This should be provided by your
service provider. Default is QPSK.
[5] RR - Rx Symbol Rate: The symbol
rate at which the demodulator receives at. It
can be entered in sps (symbols per second).
When changing the symbol rate, the data rate
in the Basic Configuration will also change.
Symbol rate is related to data rate using the
following equation:
Symbol Rate = (Data Rate / (Code Rate x
Modulation Index)) x Reed-Solomon
Overhead
For example, the symbol rate of a 70 Mbps,
Viterbi 7/8, QPSK transmission is
Symbol Rate = (70000000 / ((7/8) x 2)) x
(204/188) = 43404256 sps
[6] SD - Descrambling Type: enables or
disables DVB descrambling algorithm
applied to receive data stream. Default is
DVB descrambling.
[7] DFS - Demod Filter Select: Selects
the spectral shape for the digital filter. Used
to optimize filter shapes between modulator
and demodulator. Default is ComStream.