Comtech EF Data SDM-300L3 - Manual (Page 90)

SDM-300L3 Satellite Modem Revision 1
Front Panel Operation MN/SDM300L3.IOM
4–22
FUNCTION SELECT: CONFIGURATION: DEMODULATOR:
IF LOOP BACK
IF LOOP BACK
OFF
IMPORTANT
This is a Test Mode.
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
IBS, IDR or 308-2
INTERFACE
ENCODER/
MODULATOR
TRANSMIT RF
EQUIPMENT
ANTENNA
AC POWER POWER SUPPLY
MICRO-
COMPUTER
REMOTE SERIAL
INTERFACE
FAULT INDICATORS
RECEIVE RF
EQUIPMENT DEMODULATOR/
DECODER
SATELLITE MODEM
Figure 4-5. IF Loopback
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.