POWER LINE CARRIER/LORAN-C INTERFERENCE MITIGATION TECHNIQUE
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2001-Oct-10
Electric utllltles utlllze a technique called direct transfer trip to provide protective relaying of their hlgh voltage transmlsslon system. As part of this technique, a guard tone or CW power line carrier in the LF frequency band is injected on the transmission line at a level of approximately 1 watt. A problem arlses in operating a LORAN-C navigation receiver in the vicinity of such transmission lines since the LORAN-C receiver also operates in the LF frequency band. In particular, the phase locked loops utilized by the LORAN-C receiver to track the navigation signals lose lock and the LORAN-C receiver provides er- roneous navigation information. This problem can be eliminated by adding a blanking circuit of ap- propriate timing at the output of the transmitter utilized to inject the guard tone into the transmission line to create short gaps in the guard tone (see Figure 1).