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SDM-300L3 Satellite Modem
Front Panel Operation
FUNCTION SELECT: CONFIGURATION: DEMODULATOR:
IF LOOP BACK
IMPORTANT
Programs the modem for IF loopback operation. When IF loopback is turned on, the
demodulator input is connected to the modulator output through an internal attenuator
and the modulator continues to TX a signal. The demodulator is programmed to the same
frequency as the modulator. When IF loopback is turned off, the demodulator is tuned to
the previous frequency and is reconnected to the IF input. Refer to Figure 4-5 for a block
diagram of IF loopback operation.
Note: IF loopback nullifies RF loopback.
CUSTOMER
DATA
REMOTE SERIAL
INTERFACE
FAULT INDICATORS
SATELLITE MODEM
Note: When IF loopback is turned on, the demodulator is looped back to the modulator inside the modem and the demodulator is
programmed to the same frequency as the modulator. This test mode will verify the operation of the modem. When IF loopback is
turned off, the demodulator is programmed back to the previous frequency and is reconnected to the IF input.
IF LOOP BACK
This is a Test Mode.
IBS, IDR or 308-2
ENCODER/
INTERFACE
MODULATOR
COMPUTER
DEMODULATOR/
DECODER
Figure 4-5. IF Loopback
OFF
MICRO-
POWER SUPPLY
4–22
Revision 1
MN/SDM300L3.IOM
TRANSMIT RF
EQUIPMENT
ANTENNA
AC POWER
RECEIVE RF
EQUIPMENT
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