Shipboard Gridlock System

program. The information about these tracks can be transmitted to other units over the Link-11 net. The computer sends data to the data terminal set using 24- bit data words. The computer also receives information about remote tracks from other units in the net and displays these tracks through the display system. Shipboard Gridlock System Gridlock is the matching of track positions held by other ships with the tracks held by your own ship. Gridlock is a procedure for determining data registration correction by comparing remote tracks received from a designated reference unit to local data. Ideally, tracks received from remote units that are also displayed by onboard sensors should be transparent, that is, in the exact same position on the CRT. If the gridlock system does not provide correlation between local and remote tracks, the remote tracks may be painted twice and overlap each other, as shown in figure 4-3. Figure 4-3.—Tracks out of gridlock. Failure to maintain gridlock may be the result of inaccurate positioning data from a ship’s sensor, from the Ship’s Inertial Navigation Systems (SINS), or from the ship’s gyro. Failure to maintain gridlock may also be the result of an inaccurate operator entry. The SGS computer performs continuous automatic gridlock calculations. In the event of an SGS computer failure, the flow of Link-11 data to the CDS computer is interrupted. To restore Link-11 data flow, all SGS installations have switches installed that allow the technician to bypass the SGS computer until the fault is corrected. Link-11 Security Device A standard model security device, such as the TSEC/KG-40, commonly referred to as the KG-40, is used with the Link-11 system. When the DTS is transmitting data, the KG-40 receives parallel data from the CDS computer, encrypts the data, and sends it to the DTS. When the participating unit (PU) is receiving data, encrypted data is received from the DTS, decrypted, and sent to the CDS computer. Because of the specialized training and security requirements of cryptographic equipment, we will not cover the internal operation and controls of the security device. Data Terminal Set (DTS) The data terminal set (DTS) is the heart of the Link-11 system. The DTS is the system modulator/demodulator (MODEM). the CDS computer sends 24 bits of data to the DTS via the SGS computer and the encryption device. The DTS adds six bits of data for error detection and correction. These six bits are called hamming bits. The 30 bits of data are phase shift modulated into 15 audio tones. These 15 data tones and a Doppler correction tone are combined into a composite audio signal, which is sent to either the UHF or HF radio for transmission. The DTS receives the composite audio signal from the radio and separates the 15 data tones and the Doppler correction tone. The 15 data tones are demodulated into 30 data bits. The six hamming bits are checked for errors and the 24 data bits are sent to the CDS computer via the encryption device and the SGS computer. Link-11 Communications Switchboard The communications switchboard provides for manual switching of the data terminal set and individual HF and UHF radios. The communications switchboard provides system flexibility and casualty 4-3