Originally Posted by
Kingbird87
OK. What is SONAR then? The HC-130's Cook Tracker picked up re-entering space craft in the ionosphere, S-band signal sine waves and the ELT that was under the Sea of Ohkotsk. The radio frequency of an ELT is 121.5 and 243.0. The pinger is ultra low frequency and you may not hear it on your radio, but a P-3 or my HC-130N did. It was built to find objects under the water, of the highest national priority.
SONAR is soundwaves...
The "pinger" is an acoustic device as well, not RF.
Even VLF only goes down to 20 meters below the surface. Submarines use that for communications when they would come up near the surface. Only ELF frequencies can penetrate down to submarine operating depths. VHF and UHF have far less penetration that is limited to just below the surface.