multi-station POFA is transmitted, atmospheric
interference, ship’s position, antenna location, and
EMI are just a few of the things that can induce errors
in the radio signal. Determine the receive error factor
by dividing the number of words with errors by the
number of words received. When the receive error
factor is less than 1 percent, consider the POFA
successful.
When the printout indicates that data was received
from an unrecognized station (UNREC STA), the
technician should check the number of words
received. The multi-station POFA transmit buffer
consists of 230 words. One buffer of 230 words from
an unrecognized station is acceptable and generally
does not indicate a problem. More than one buffer
may indicate a problem, but multiple buffers from an
UNREC STA can also be caused by interference on
the frequency.
The printout will also indicate the parity status of
the words received in error. During the POFA, since
the computer knows the contents of the received data
block, it performs a parity check on all received
words. These parity checks are compared with the
parity status received from the DTS. The printout
indicates these parity checks. The heading PARITY
STATUS OF ERROR WORDS lists the number of
error words detected by the DTS and the parity (1, 2,
or 3).
The heading PARITY STATUS OF
CORRECT WORDS indicates the computer parity
check of words received as correct from the DTS.
When an error is detected, the number of words in
error for each of the three parity status conditions are
listed here. The final part of the printout indicates the
remote station reports. These reports are sent by other
stations as part of the data transferred during the
POFA.
Since a multi-station POFA is subject to various
types of interference, both natural and man-made,
several attempts may be required for you to achieve
acceptable results. Shifting NCS and repositioning
the ships are just two of the actions that could
contribute to achieving a successful multi-station
POFA.
THE LINK-11 MONITORING
SYSTEM (LMS-11)
“The link is down” is a statement that can strike
fear into even the most seasoned technician. As we
have seen, the operation and maintenance of a high-
quality link can be affected by many factors. For
years, operators and technicians commonly blamed
each other for poor link operations. Some typical
Link-11 problems areas follows:
Participating units (PUS) not responding to
call-ups
Garbled data
The link goes completely dead, normal
operation ceases
Inability to establish a net
Excessive net cycle time
When such a problem occurred, the Link-11
technician would run a single station POFA and
declare that the DTS was sound and it must be the
other ship, a poor frequency, or an operator error. The
operator would blame the frequency or the NCS.
Other units would say the problem was another
platform jamming the entire net. Typical strategies
used to solve link problems usually began with a
recommendation to change frequency. When this
strategy failed to solve the problem, the next step was
to change the NCS. If the problem still existed, the
NCS would eliminate PUs from the net, one at a time
until the problem unit was identified. All of these
actions took time and were hit-and-miss techniques.
This tendency of trial-and-error troubleshooting and
pointing fingers defined the need for a reliable visual
system of monitoring the Link-11 network.
This need was filled with the development of the
Link Monitoring System, AN/TSQ-162(V)1,
commonly called the LMS-11. The LMS-11 provides
an operator or a technician with a real-time visual
display of the Link-11 network while it is operating.
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