Comtech EF Data SDM-100A - Manual (Page 111)

SDM-100A Satellite Modem Operation
Rev. 0 3–77
TRANSMIT RF
EQUIPMENT
CUSTOMER
DATA
INTERFACE ENCODER/
MODULATOR
TX = 70 MHz
RX = 73 MHz
RF_LBK = 70 MHz
ANTENNA
AC POWER
POWER
SUPPLY
MICRO-
COMPUTER
REMOTE
SERIAL
INTERFACE
FAULT
INDICATORS
RECEIVE RF
LOOPBACK CHANGES DEMOD RECEIVE
FREQUENCY TO 70 MHz WITHOUT LOSING
ORIGINAL PROGRAMMING INFORMATION.
MODEM REQUIRES AN EXTERNAL PATH
TO LOCK. THIS IS DONE EITHER AT THE
MODEM INPUT, OR FROM THE SATELLITE
.
EQUIPMENT
DEMODULATOR/
DECODER SATELLITE
SDM-100A
DATA MODEM
Figure 3-26. RF Loopback
Note: When RF loopback is turned on, the demodulator receive frequency is programmed to the same frequency as
the modulator transmit frequency. This test mode allows the user to verify the satellite link without changing the
programmed frequency of the demodulator. When RF loopback is turned off, the demodulator is programmed back to
its previous frequency.