Measurements of Vertically Polarized Electromagnetic Surface Waves Over a Calm Sea in HF Band. Comparison to Planar Earth Theories

Radio communication over Earth along mixed-paths in the HF band is a relevant subject today. In this communication, we present measurements of electric field propagating over sea water in HF Band compared to K.A. Norton, R.W.P. King and G. Millington´s theories, thanks to a reliable measurement setup. The transmitting antennas are located on the coast while the receiver antenna is installed on a boat steering a constant course. The electric field measurements are carried out with a loop antenna and we measured the field strength attenuation versus distance between the transmitter and the boat along a sea water path. In order to take into account the media change (the coast and the sea water), Millington´s solution has been added to King´s and Norton´s theories with the planar Earth model. The measurements performed at three frequencies (10 MHz, 20 MHz and 30 MHz) and the calculations are in a good agreement. At 10 MHz, the “smoothly” attenuation is shown and is very well correlated with the theory. The EM field decrease as 1/d² has been clearly observed at 20 MHz and 30 MHz.