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CDM-600L Satellite Modem
DST Setup
18.2
LO, Mix and Spectrum (Inversion) Settings
The CDM-600L Satellite Modem permits programming of terminal (satellite) frequencies
instead of the L-Band frequencies. This is useful because it allows direct entry of the
assigned TX and RX frequencies. Three parameters are adjusted to setup the modem with
the BUC/LNB. These parameters are:
The LO and MIX are entered into the modem to program the satellite frequency for the
terminal. Consult the BUC manufacturer's specifications for BUC LO specifications.
Whenever MIX = - the spectrum of the carrier is inverted. The CDM-600L easily corrects
for this with the Invert ON/OFF selection located under the
Configuration:TX:TX-IF and Configuration:RX:RX-IF menus.
Match the Tx inversion to the MIX in the BUC and the Rx inversion to the MIX in the
LNB using the following:
As a general rule it is best to radiate the spectrum toward the satellite in the Normal
spectral sense. Then transmission links with any other corresponding sites are always
consistent at the satellite interface.
When doing RF loopback testing over the satellite or end-to-end the settings are correct
with this setup. If there is a single inversion in the modem, however, for operation over
the satellite, it will be necessary to temporarily match the spectral inversion of modulator
and demodulator when performing IF loopback testing.
Note: The modem will only allow programming of terminal frequencies that are within
its valid L-Band frequency limits.
♦ LO: Local Oscillator Frequency.
♦ Mix Sign: + or -, determines whether the L-Band carrier is added or
subtracted from the LO to translate to the satellite frequency.
♦ Mod Spectrum and Demod Spectrum (Inversion); needed to correct for any
inversion caused by the frequency translation.
♦ MIX = "+" when LO < Satellite Operating Frequency
♦ MIX = "-" when LO > Satellite Operating Frequency
♦ Spectrum = Normal when MIX = +
♦ Spectrum = Invert when MIX = –
18–3
Revision 2
MN/CDM600L.IOM
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