THE LINK-11 MONITORING SYSTEM (LMS-11)

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. 3-6