Effect of skywave interference on the coverage of Loran-C

Receivers for the Loran-C terrestrial radio-navigation system are designed to distinguish pulses received by groundwave propagation from skywave interference components which arrive later. The technique, however, has significant limitations when implemented in receivers of finite bandwidth. The International Electrotechnical Commission and other authorities specify minimum standards of receiver performance in this respect. Drawing data from a range of sources, including Decca Navigator records, the paper proposes methods of predicting skywave-to-groundwave ratio and skywave delay, the key elements of these specifications. This information is used to calculate the range limits due to skywave interference at various times and seasons, considering individual transmitters and both present and proposed Loran-C chains. The results demonstrate that the use of high transmitter powers is generally not justified. The paper points out ambiguities in the current minimum performance standards for receivers. It demonstrates that they are inadequate to protect users against the effects of skywave interference and identifies areas in which improved specifications are required