Comtech EF Data SDM-300A - Manual (Page 112)

SDM-300A Satellite Modem Revision 6
Front Panel Operation MN/SDM300A.IOM
5–18
FUNCTION SELECT: CONFIGURATION: DEMODULATOR:
IF LOOP BACK
IF LOOP BACK
OFF
IMPORTANT
This is a Test Mode.
Programs the IF Loopback Operation: On or Off. When IF loopback is turned on, the
demodulator input is connected to the modulator output through an internal attenuator. The
demodulator is programmed to the same frequency as the modulator. An attenuator within the
modem connects the IF Out to the IF In. When IF loopback is turned off, the demodulator is
tuned to the previous frequency and is reconnected to the IF input. IF loopback nullifies RF
loopback.
Figure 5-5 shows a block diagram of IF loopback operation.
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 5-5. 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.