Removal and replacement of ADU modules
8-16 Chapter 8: Service & maintenance 99-145912-A
1. GPS module.
This module is positioned near the service switch at the bottom of
the pedestal. It converts the GPS satellite signals into current
position data.
2. VSAT Interface Module (VIM2).
The purpose of the VIM2 is to interface between the ADU coaxial
cable carrying several signals (DC, modem, RX IF, L-band TX) and the
cable to the LNB/BUC, and the PCM. The VIM takes the received L-
band transponder signal from the LNB and converts it to a higher
frequency and allows the whole L-band transmitter band to be
routed to the BUC.
For narrow band signal or non-DVB tracking the VIM has a power
detector as signal strength indicator. It also contains a DVB-S/S2
demodulator.
The VIM consists of the following blocks:
• Power supply block for on board circuits, supply to PCM board
and regulated external output to LNB (with band switching) and
BUC.
• Narrow band channel detector and a DVB-S/S2 tracking receiver
with tuner and demodulator
• LNB Receive signal up-converter with mixer and PLL.
• Cable attenuator section to control the output power variation to
the BUC.
• FPGA section to control the functions of the VIM including DVB-
S/S2 transport stream decoding.
• Filters for splitting and combining the DC, modem, received up
converted IF from the LNB and the transmit signal to the BUC.
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