RECOGNIZING LINK-11 NET PROBLEMS

distance. This allows the operator to view the effects of the noise. The power of the noise tones is also indicated by open yellow bars. To enter the spectrum display, depress the SPECT key on the keyboard. Several options are available to the operator by entering data into the header fields of the spectrum display. The operator may designate the address of the NCS. The default address is 77. The operator can also select a particular sideband (USB, LSB, or DIV) for display. By using the RESTRICT field, the operator can restrict the display to only data frames or only preamble frames, or choose no restrictions. The PU field allows the operator to designate a particular PU for display. If 00 is entered into the PU field, the data display is continuously updated with samples from the entire net. Carrier Suppression Display The carrier suppression display measures how successfully the carrier frequency is suppressed. The carrier suppression measurements can only be made during Net Sync. To measure the carrier suppression, the radio must be off-tuned by -500 Hz for the upper sideband and +500 Hz for the lower sideband. This off-tuning allows the program to measure and compare the relative power of the carrier frequency and the 605-Hz tone of the preamble. RECOGNIZING LINK-11 NET PROBLEMS The LMS-11 is very useful in evaluating Link-11 net quality. As you have seen, the various on-line modes can help you determine various problems. These include a station that is consistently missing call-ups, poor signal-to-noise ratio, and low power from a unit. Some common Link-11 problems and the LMS-11 display are covered in the next few paragraphs. Figure 3-14 shows an example of how a PU not responding to call-ups would appear on the LMS-11 operating in the Link Monitor mode. When a PU does not respond to a call-up, the reason maybe that the incorrect PU number was entered at the NCS or at the DTS of the unit. It can also be caused by a poor receiver at the PU, causing the PU to not receive its call-up. A third problem could be a weak transmitter at the PU, causing the NCS to not receive the response and therefore, repelling the PU. Figure 3-14.—A PU not responding to NCS call-up. Figure 3-15 shows the display that appears when a PU is responding to NCS call-ups, but the report contains no data. Causes of this problem could be that the KG-40 has an alarm, the CDS program is down, or the problem is in the CDS computer to DTS patching. Figure 3-15.—A PU responding with no data. When the NCS fails to receive a stop code from a PU, a stoppage of the net occurs, as shown in figure 3-16. If this condition occurs repeatedly and can be traced to a single PU, the NCS should delete the PU until the stop code problem in the DTS is corrected. Figure 3-16.—A net stoppage caused by NCS not receiving a stop code. Figure 3-17 shows several PUs not responding to call-ups. Some of the causes for this condition could 3-18