"Chapter 2: Ground Waves". Introduction to Wave Propagation, Transmission Lines, and Antennas. Naval Electrical Engineering Training, Module 10. Naval Education and Training Professional Development and Technology Center. September 1998. p. 2.16. NavEdTra 14182. Archived from the original(PDF (archive zipped)) on 2018-05-11.
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"Chapter 2: Ground Waves". Introduction to Wave Propagation, Transmission Lines, and Antennas. Naval Electrical Engineering Training, Module 10. Naval Education and Training Professional Development and Technology Center. September 1998. p. 2.16. NavEdTra 14182. Archived from the original(PDF (archive zipped)) on 2018-05-11.