AMT-70/AMT-73/AMT-75 Installation and Operation
CAUTION:
With LNB power enabled, there is a potentially damaging DC voltage applied to the
demodulator input. When connecting test equipment, or a local modulator (or any
DC coupled devices), always use appropriate DC blocks, and disable LNB powering.
The following commands are available to provide DC, tone or reference to the LNB/BDC:
Command Arguments Description
RLNBP OFF, ON LNB DC Powering
RLNBVP OFF, ON LNB Vertical Polarization
RFREF OFF, ON LNB 10MHz Reference
RLNBTO OFF, ON LNB 22kHz Tone
2.7.4 Demodulator L-Band Input (AMT-73L)
The L-Band input signal is presented to J2 (Type TNC female, 50Ω) on the rear panel of the modem.
There are currently no provisions for providing LNB/BDC DC power in the AMT-73L.
2.7.5 Demodulator 70/140 MHz IF Input (AMT-70 and AMT-75)
The demodulator can optionally be ordered with 70/140MHz inputs, in place of the L-Band inputs.
When used in 70MHz input mode, the maximum bandwidth is 36MHz while in the 140MHz mode the
full 54MHz or 72MHz range can be used.
These inputs are capable of operating with the standard C-, X- or Ku-Band BDC, with their outputs
producing 70 MHz on the output. The figure below shows a typical installation using the 70 MHz inputs
and the C-, X-, or Ku-Band down converters with 70 MHz outputs.
2.8 Bringing the Modulator Online
NOTE: Before attempting to bring the modulator on line, the operator should
become familiar with the operation of the modem while off line. Refer to Chapter
3 through Error! Reference source not found. to obtain a thorough understanding
of modem operation using a terminal emulator (or PC with terminal emulation
program).
When bringing a transmit carrier on line (AMT-70L with BUC power supply), the following sequence
must be followed:
Power on the modem for five minutes to allow the oscillator to stabilize.
Before connecting the L-band cable to the BUC, verify that:
o The frequency of the modulator and demodulator are correctly set
o BUC power is off (bucpower off)
o 10 MHz reference is off (tfref off)
Set modulator power to -25 dBm (tlevel -25)
If required and if the option is fitted, turn on DC power to BUC (bucpower on).
If required and if the option is fitted, turn on 10 MHz reference to the BUC (tfref on).
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Increase modulator output power to desired level (tlevel < desired level >).
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General