Nonreciprocal characteristics of a 1500 km HF ionospheric path

The reciprocity theorem of electromagnetism is not generally true for ionospheric propagation paths, and this has been demonstrated from time to time since the earliest days of HF radio. In the past ten years, particularly, significant progress in understanding the characteristics of HF nonreciprocity has been made by various workers who have studied the two-way fading of pulsed signals propagated by single ionospheric paths. Meadows [1956] and Balser, Smith, and Warren [1958] observed correlated two-way fading of E and F layer signals but on other occasions the two-way fading was uncorrelated. Jull ind Pettersen [1964] found the two-way fading of F layer signals transmitted between horizontal antennas was almost inversely correlated when both ordinary o and extraordinary e waves were present in the signal. When only one wave was present in the signal, the two-way fading was correlated. These latter results were interpreted on the basis of a recent ray theory of reciprocity [1964]. This letter presents evidence to show that ray theory can also account for the nonreciprocal characteristics of a 1500 km path between Atlanta, Ga. (33'45'N., 84O, 3O'W), and Ipswich, Mass. (42" 45'N., 70" 45'W.).