Comtech EF Data SDM-300A - Manual (Page 111)

SDM-300A Satellite Modem Revision 6
Front Panel Operation MN/SDM300A.IOM
5–17
FUNCTION SELECT: CONFIGURATION: DEMODULATOR:
RF LOOP BACK
RF LOOP BACK
OFF
IMPORTANT
This is a Test Mode.
Programs the RF Loopback Operation: On or Off. Upon entry, the current status of the RF
loopback is displayed. Press [
↑] or [↓] to make the selection. Press [ENTER] to execute the
change.
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. RF loopback nullifies IF loopback. Figure 5-4 shows a block diagram of RF
loopback operation.
CUSTOMER
DATA
IBS or IDR
INTERFACE
ENCODER/
MODULATOR
TX = 70 MHz 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.
RF LBK = 70 MHz
RX = 73 MHz
DATA
Figure 5-4. 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.