Transverse electric waves for VLF/LF communication between aircraft

This report compares the excitation and propagation of VLF/LF transverse electric (TE) and transverse magnetic (TM) long waves in the earth-ionosphere waveguide. It calculates the dependence of TE and TM mode parameters on three factors: (1) ground conductivity, (2) state of the ionosphere, and (3) elevation of terminals above the ground. It also briefly addresses the effects of atmospheric noise and ground-based jammers on the performance of TE links. Results are given for frequencies between 20 and 50 kHz. Only TM signals are efficiently radiated by ground-based transmitters. However, TE signals are strongly excited by nearly horizontal trailing-wire antennas at elevations exceeding 20 kft and, thus, can be important for air-to-air links. Poorly conducting ground heavily degrades TM propagation, but it will not affect TE propagation if the terminals are elevated at least 5000 ft. TE signals are, therefore, better suited than TM signals for air-to-air links that traverse Greenland and much of Canada. For paths over highly conducting ground, TM signals suffer less degradation than TE signals during intense disturbances; for ground conductivities less than about .0001 mhos/m, however, TM signals are more adversely affected. TE signals also provide protection against ground-based jammers under disturbed ionospheric conditions where geomagnetic conversion is slight.