Medium frequency travel longer distances via skywave propagation, in which radio waves radiated at an angle into the sky are reflected (actually refracted) back to Earth by layers of charged particles (ions) in the ionosphere, the E and F layers. However at certain times the D layer (at a lower altitude than the refractive E and F layers) can be electronically noisy and absorb MF radio waves, interfering with skywave propagation. This happens when the ionosphere is heavily ionised, such as during the day, in summer and especially at times of high solar activity, At night, especially in winter months and at
History of radio proposed electromagnetic or Hertzian waves as a navigation aid or means of communication, with Crookes writing on the possibilities of wireless telegraphy based on Hertzian waves in 1892. After learning of Hertz' demonstrations of wireless transmission, inventor Nikola Tesla began developing his own systems based on Hertz' and Maxwell's ideas, primarily working toward a means of wireless lighting, and power distribution. Tesla, concluding that Hertz had not demonstrated airborne electromagnetic waves (radio transmission), went on to develop a system based on what he thought was the primary conductor, the earth. In 1893 demonstrations of his ideas, in St. Louis, Missouri