Comtech EF Data SDM-2020 - Manual (Page 145)

SDM-2020 Satellite Modulator Revision 7
Data Interfaces MN/SDM2020M.IOM
11-10
11.1.6 T
EST
M
ODES
11.1.6.1 I
NTERFACE
L
OOPBACK
The modulator/demodulator provides an “interface loopback” test mode of operation.
When loopback mode is executed (turned ON), Send Data (SD) at the input to the
interface is routed to both the interface RX Data (RD) output and the host modulator data
input. Send Data (SD) is routed through as much of the interface circuitry as possible
before being returned to the RX Data (RD) output. This mode of operation does not
disrupt transmission of data over the satellite link when installed in a modulator.
• In a modulator application, the RX Data rate and line coding is automatically
set to be compatible with the TX settings.
•
In a demodulator application, TX data rate and line coding is automatically
set to be compatible with RX settings and the buffer reference clock is set to
TX terrestrial.
11.1.7 T
ERRESTRIAL
I
NTERFACE
T
YPES
11.1.7.1 S
END
D
ATA
(SD), R
ECEIVE
D
ATA
(RD),
AND
E
XTERNAL
C
LOCK
C
ONNECTORS
J3, J4,
AND
J6
The Send Data (SD) (J3), RX Data (RD) (J4), and EXT CLK (J6) connectors are all BNC
type connectors and are terminated into 75
Ω.
11.1.7.2 A
UXILIARY
F
UNCTIONS
C
ONNECTOR
, J5
The connector is a 9-pin sub-miniature D female, with threaded jack nuts.
Modulator Fault (MF) and Demodulator Fault (DF) are single-ended open collector
signals, where:
Voh=12V max. and Vol=0.5V max. @ Iol=8 ma.
A pull-up resistor external to the equipment is required.
For (MF) and (DF) a fault is indicated by an OFF (Vout = Hi) open collector transistor
and the normal OK state is indicated by an ON transistor (Vout = Lo).
The Carrier Detect (CD) signal is a TTL output. When CD is high, it indicates the
demodulator is locked.
TX IF ON/OFF: It is possible to use RTS signal on the auxiliary connector
for turning the transmit carrier ON or OFF. The RS signal is enabled for this mode of
operation and the polarity of the RS signal is programmed by the user.