These articles are in downloadable PDF format
Thru-the-Earth 2-way voice communications with cave divers using acoustic diver voice gear converted to RF.
Real time tracking of an underwater beacon. This was written for tracking Bill Stone's Endurance vehicle under ice in Lake Bonnie Antarctica, but also applies to divers in underground springs and to dry caves as well.
Determining the Optimum frequency for Thru-the-Earth communications with loop antennas - theory and actual tests.
Obtaining and using an Experimental license from the FCC in the years prior to Radio Amateur access to the 2200 and 630 meter bands
Calculating the inductance of ferrite rod antennas and measuring the approximate permeability of ferrite rods.