User Guide: Technical Reference
SECTION 3 OPERATING THE
ioLink 4
PRELIMINARY
Customer Support (202) 333-7031
-3-6
3.1.3.3 TEST Menu Item Descriptions
The TEST menu permits the user to place the modem into configurations that enable the testing of the
modem to confirm the operating status. These modes are useful when the data input device is capable of
providing a bit stream that may be detected and checked for bit errors (e.g., a Bit Error Rate Tester).
The tests that are available in the TEST and ADVANCED menus are powerful tools for diagnosing many
problems in the system. These tests are especially helpful in determining where a problem may lie in the
system (i.e., in the modem unit, user equipment, local or remote end, etc.). These tests must be
performed with the use of a Bit Error Rate Tester (BERT). The BERT can be connected to either the DSX
or G.703 interfaces on the back of the modem unit to read out the conditions of the test. The BERT can
be used to provide bit streams for performing a test, or it can be used simply to test the signal already
present in the system.
The following block diagrams are useful tools for visualizing what each test is doing and how they may be
used in getting essential information to check the system. Items inside the dashed box denote modem
unit sections. The arrows denote the signal path. An “X” in the path shows where the signal is
terminated.
a. Full Loopback
Selecting ON for this test mode places the modem into a loopback mode at the spreading chip in the
baseband processing section. In this mode, the input data is processed by the LIU, FEC, and spreading
circuitry, then looped back through the de-spreading FEC and LIU circuitry and returned to the input
device. This allows the user to determine whether the line interface, forward error correction, and
spreading sections of the modem are operating correctly.
User
RF
Spreading
Section
LIU
FEC
IF
Section
Figure 3-2. Full Loopback
