13
LDM-144LR
2.3.3 S
ELECTABLE
L
EVEL
T
RANSMIT
A
MPLIFIER
Two options are available for the transmit signal level: 0 and -6 dBm. The
transmit signal level is controlled by the XMT LEVEL jumper (J11). Receive
signal gain is controlled by the RCV LVL jumper (J9) and has two selectable
options: 0 and -6 dBm.
2.3.4 V.54 D
IAGNOSTICS
V.54 loops are activated either by the manual front panel push-buttons or
through the DTE interface. The push-button controlled loopbacks can be
enabled or disabled by the SWITCH jumper (J2), while the DTE controlled
remote and analog loopbacks are enabled and disabled by the RLB (J6) and
the ALB (J5) jumpers respectively. When the LDM-144LR is used as a tail-end
to a digital network, the V.54 DLY jumper (J7) in the modem closest to the
network is set to ON to prevent other equipment from receiving the V.54 data
sequence and inducing it into the loop.
2.3.5 T
EST
P
ATTERN
G
ENERATOR AND
R
ECEIVER
The Test Pattern Generator enables easy and quick testing of the local
modem and the communication link. When the PATT pushbutton on the
front panel is activated, the circuit sends a standard 511-bit pseudo-random
pattern and checks its response. If errors are detected, the ERR indicator
remains ON or blinks.
The test can be carried out in local analog loopback, in remote digital
loopback, or in normal point-to-point operation opposite a remote LDM-
144LR. For the latest test to take place, press the PATT pushbutton on the
remote unit or connect a Bit Error Rate Tester BERT, which generates and
receives a standard pseudo-random 511-bit pattern.
2.3.6 S
ELECTABLE
C
ARRIER
D
ETECT
S
ENSITIVITY
Carrier Detect Sensitivity is controlled by the CD SENS jumper (J4). Setting
J4 to LOW will activate DCD over short ranges. Setting J4 to HIGH will
activate DCD up to the ranges in
Table 2-1
.
