DVOR is an FM and Phase Modulated system, while CVOR is primarily AM. FM (and phase modulation) is less affected by physical installation variables of terrain, nearby structures, and aircraft movement as well as atmospheric factors. By design, AM varies according to all of the above (and more), while frequency modulation radio transmissions over the same locations may vary in signal strength, but the modulated carrier remains unchanged.
Last edited by vapilot2004; 3rd July 2016 at 02:15.