Processing of real ELT signals for SARSAT

A significant number of lives have been saved by using a new system called search and rescue satellite aided tracking (SARSAT). The program initially involved Canada, the United States and France with the Soviet Union forming a parallel project called COSPAS. Since then, the United Kingdom, Norway and Sweden have joined the program and it is expected that the system will be used worldwide. The performance of several different signal processors using real emergency locator transmitter (ELT) signals is evaluated. These signals have an unusual modulation characteristic which produces unwanted interference due to sidebands. The periodogram gives good performance for coherent ELT signals especially when a ranking and averaging technique is applied. However, the method is incapable of determining the carrier frequency for noncoherent ELT signals. Use of the maximum entropy method (MEM) in detecting these noncoherent ELT signals is demonstrated and it is shown that an effective carrier frequency can be deduced when the signal-to-noise ratio is high.