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Ghost
Signal ReviewGhost signals or perhaps more accurately termed "carrier signals", or even random noise can cause considerable difficulty for electronic search personnel. Occasionally you may be dispatched to locate a "carrier only" signal source on 121.5 MHz or 243.0 MHz that is interfering with the SARSAT system.
A "carrier only" ELT / EPIRB signal is one that has no identifying audio or as unusual transmission characteristics. This is often the result of damage caused as a result of a crash or malfunction. It would be like holding a microphone button down but not saying anything. You can track these signals in the same manner as you would do with a sweep tone ELT / EPIRB signal.
Carrier only signals have the same signal propagation characteristics and most direction finding (DF) equipment will react in the same way as it would with an ELT / EPIRB that is operating normally. These carrier signals, if not from a malfunctioning ELT / EPIRB may be very high powered, so watch your signal strength setting carefully and adjust the sensitivity control accordingly to avoid over-loading the receiver.
The difficulty in tracking comes with not being able to hear anything but perhaps limited static or other similar noise, and therefore you will be unable to positively identify the signal you are tracking. Start out in the same manner you do on any ELT / EPIRB tasking. Watch the DF or signal strength meter for any deflections that may indicate that the receiver is responding to a signal.
Periodically make a 360 degree turn on the chance you have a centered DF meter initially. The direction finder will track random noise as well as a legitimate signal, so you must determine which you have. If you believe the DF is tracking a carrier only signal on 121.5 MHz, change to 121.6 MHz. If the DF has a signal on 121.5 MHz, the meter reading will change when you select 121.6 MHz. If the DF is hearing random noise, the meter readings will remain roughly the same on both frequencies.
Once you have determined that you have a "real" signal on 121.5 MHz, use the same methods to track it as you do with an audible sweep tone ELT signal. It will be considerably more difficult because you will have to rely on the meter readings with no audio clues to help you.
Paul D Turner
