Comtech EF Data SDM-300L3 - Manual (Page 89)

SDM-300L3 Satellite Modem Revision 1
Front Panel Operation MN/SDM300L3.IOM
4–21
FUNCTION SELECT: CONFIGURATION: DEMODULATOR:
RF LOOP BACK
RF LOOP BACK
OFF
IMPORTANT
This is a Test Mode.
Programs the modem for RF loopback operation. When RF loopback is turned on, the
demodulator is programmed to the same frequency as the modulator. When RF loopback
is turned off, the demodulator is tuned to the previous frequency. Refer to (Figure 4-4)
for a block diagram of RF loopback operation.
Note: RF loopback nullifies IF loopback.
Upon entry, the current status of the RF loopback is displayed. Press [
↑ ] or [ ↓ ] to make
the selection. Press [ENTER] to execute the change.
Figure 4-4. RF Loopback
Note: When RF loopback is turned on, the demodulator receive frequency is programmed to be the same frequency as the
modulator transmit frequency. This test mode will verify the satellite link without changing the programmed frequency of the
demodulator. When RF loopback is turned off, the demodulator is programmed back to the previous frequency.
CUSTOMER
DATA INTERFACE
ENCODER/
MODULATOR
TRANSMIT RF
EQUIPMENT
ANTENNA
AC POWER POWER
MICRO-
COMPUTER
REMOTE SERIAL
INTERFACE
FAULT INDICATORS
SUPPLY
RECEIVE RF
EQUIPMENT DEMODULATOR/
DECODER
SATELLITE MODEM
LOOPBACK CHANGES DEMOD
RECEIVE FREQUENCY TO
70 MHz WITHOUT LOSING
ORIGINAL PROGRAMMING
INFORMATION.
TX = 1200 MHz
RX = 1225 MHz
RF LBK = 1200 MHz
DATA