LINK-11 NET OPERATING MODES

Figure 2-4.—Link-11 data flow for the transmit cycle. keys the transmitter using the radio set keyline, and passes the audio tones, via the communications switchboard, to the transmitter for modulation to the RF carrier signal. The radio set keyline is a signal that switches the radio to the transmit mode. When the signal is stopped, the radio reverts to the receive mode. When you are using the HF band, the radio frequency signal modulation uses amplitude modulation independent sideband; that is, the upper sideband (USB) and lower sideband (LSB) are transmitted independently in an effort to overcome propagation-caused signal losses. The UHF radio uses frequency modulation; therefore, only the USB is used. Receive Cycle When a transmitted signal is received, the receiver demodulates the audio tones from the RF carrier and passes them via the communications switchboard to the DTS. The DTS demodulates and demultiplexes the audio tones into digital data. The digital data is sent to the cryptographic device where it is decrypted and sent to the CDS computer for processing. LINK-11 NET OPERATING MODES Before we look into the actual operation of the data terminal set, you need to have some knowledge of the Link-11 modes of operation and how the messages are formed. Link-11 employs networked (net) communications techniques for exchanging digital information among airborne, land-based, and shipboard systems. As you have seen, the amount of hardware required to support Link-11 operations is relatively small; however, establishing and maintaining a successful link can be very complex. Establishing a Link-11 Net The establishment of a successful link involves the interaction and teamwork of the operators and technicians of several units working towards the common goal. If one unit is having trouble with the link radio, data terminal set, or other equipment, it can make the entire link unreliable. When a task force is about to deploy, the task force commander will issue a message that has the necessary information required to establish Link-11 communications. The information in this message includes a list of primary and secondary frequencies, designation of the initial net control station, an initial gridlock reference unit (GRU) designation, PU identification and addresses, an initial data link reference point (DLRP), and required operating procedures. Voice communications are required for net control and coordination during initialization. When the task force is formed, the picket stations inform the net control station (NCS) of their readiness to establish link operations. Upon establishing communication with all units, NCS transmits Net Synchronization (Net Sync). If the NCS is using corrected timing (normal mode), the Net Sync verifies the communications path between NCS and all picket units. If a picket unit cannot receive Net Sync, it cannot participate in the net. Net Test should follow Net Sync. Net Test is used to confirm connectivity between the Link-11 units. Units having difficulty in receiving Net Sync or Net Test should report to NCS that they are not able to participate in the net and then begin corrective action. 2-5