Comtech EF Data SNM-1001L - Manual (Page 85)

SNM-1001L Satellite Modem Revision 1
Front Panel Operation MN/SNM1001L.IOM
4–21
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.
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.
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