When Net Test is completed, all picket stations
report their status to NCS. Then NCS directs all PUS
to switch to the Roll Call mode and initiate link
operations.
Net Synchronization and Net Test are
used in the initialization of the net. The normal mode
of operation is Roll Call.
The above scenario has introduced you to several
new terms and modes of operation.
These are
explained in detail in the following paragraphs.
The following are the six modes of Link-11
operation:
Net Synchronization
Net Test
Roll Call
Broadcast
Short Broadcast
Radio Silence
Net Synchronization
The Net Sync mode of operation is used to
establish a uniform time base from which all net data
communications normally initiate. The Net Sync
mode is usually initiated when establishing a link net
after all operator entries have been properly
completed. The Net Sync transmission is manually
started by the operator on the NCS platform and
continuously transmits the Link-11 preamble until
stopped by the operator.
The preamble consist of two tones–the 605-Hz
tone and the 2,915-Hz tone. During the transmission
of Net Sync, the 2,915-Hz tone is periodically phased
shifted 180 degrees. The time between these shifts is
determined by the selected data rate and is called a
frame.
Each PU is equipped with a very accurate time
base in the form of a frequency standard (internal or
external). When the NCS transmits Net Sync, each
unit receiving the transmission synchronizes its
individual time base with the Net Sync signal. If the
picket station is operating in the corrected sync mode,
as is normally the case, the picket will check to see
that it can recognize the Net Sync signal as a means of
verifying that a good radio link has been established.
If a picket is going to operate in the stored sync mode,
it will align its stored frame timing to the timing of
the NCS, using the received Net Sync signal. Since
stored sync timing locks the picket to the time base of
the NCS, data from other pickets may be lost.
Therefore, this mode should only be used during
times of poor radio propagation or signal jamming.
After the completion of Net Sync, the next operation
performed in establishing a link is usually Net Test.
Net Test
Net Test provides an overall evaluation of the net
and equipment performance. When you are operating
in this mode, NCS will broadcast canned test data to
all pickets within the net. The data terminal set
contains a code generator that generates twenty-one
30-bit data words. Once all the words in the word
table have been generated, the process automatically
starts over and keeps running until stopped by the
operator.
Net Test will test the connectivity between all
units and the operation of the DTS. Since it is a local
test, Net Test does not check the interface between the
CDS computer and the DTS. Net Testis also helpful
to the technician for setting the audio input and output
levels of the DTS or radio set.
Roll Call
Roll Call is the normal mode of operation. In this
mode, the operator on the NCS platform enters
ownship’s address and an assigned address (PU
number) for each PU in the proper switch position.
When the link is initiated, each PU is polled for data.
Polling consists of sending a call-up message. If the
PU fails to respond, the call-up is repeated. If the PU
still does not respond, it is skipped and the next PU is
polled. When a PU recognizes its own address, the
PU will transmit its data to all the participants in the
link. When the NCS recognizes the end of the PU
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