be the following: the NCS having an incorrect PU
address entered in the DTS, low transmitter power out
from the NCS, an excessively noisy frequency, or
weak PU receivers.
Figure 3-17.Several PUs not responding to NCS call-ups.
The LMS-11 also has several off-line modes that
allow you to save data onto a disk and analyze the
data in detail. The off-line modes include a frame-by-
frame display to analyze each frame of a transmission.
This allows you to analyze the data of a particular PU
and shows the status of each bit position. Remember
that when you are doing a frame-by-frame analysis,
the data has not been decrypted.
More information on all modes of the LMS-11 can
be found the System Operation and Maintenance
Organization Level, Link Monitor
SUMMARYLINK-11 FAULT ISOLATION
This chapter introduced you to some of the tools
available to ensure the Link-11 system is operating at
The following information
summarizes some of the important points you should
LINK-11 MYTHS AND FACTS Through
time, several myths about troubleshooting Link-11
have evolved. We explored some of the myths and
tried to determine the facts. Some of the myths are as
Changing NCS solves net problems. This is
only true if the NCS is causing the net
Changing frequency solves net problems.
Again, this is true only if the frequency is
noisy or is being jammed by another
More power improves Link-11 performance.
This is a myth. In fact, too much power can
actually degrade the Link-11 net.
Dummy PUs improve link quality. Again,
this is a myth. This myth evolved from the
time of the CP-642 family of computers and
the AN/USQ-36 DTS. Back then, a dummy
PU would help improve link quality, perhaps
by providing a time delay for the computer to
process all received data.
Radio Silence reduces net cycle time. This
could be true if the unit that goes radio silent
is transmitting less than 38 frames of data. As
a rule, if a unit goes radio silent, its PU should
be deleted from the polling sequence until the
unit is ready to rejoin the net.
LINK-11 POFAS The two POFAs used in the
Link-11 system are the single-station POFA and the
SINGLE-STATION POFA The single-station
POFA is an end-around test that will test most of the
DTS, the computer input and output circuits, and the
audio path if the radio is not removed from the test
path. A single-station POFA does not check the
receive timing circuits. When a single station POFA
is completed, a printout is produced that lists the
errors detected during the test. To be considered
successful, a single station POFA should always run
with zero errors.
MULTI-STATION POFA A multi-station
POFA is a test between two or more units. The multi-
station POFA closely represents normal link
A multi-station POFA requires
coordination among all units participating. All units
should be within 25 miles of each other when
attempting a multi-station POFA. Since the multi-
station POFA actually transmits data over the air, it is
subject to many types of interference, and several
attempts may be required before acceptable results are