In the US, if you have a General class ham radio license, you could do it on the 7Mhz frequency if your antenna is relatively close (less than 1/4 wavelength) t

In the US, if you have a General class ham radio license, you could do it on the 7Mhz frequency if your antenna is relatively close (less than 1/4 wavelength) to the ground. See https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=2ahUKEwivkIrE79zoAhU0HjQIHUFnAYsQFjABegQIBBAB&url=http%3A%2F%2Fw4cae.com%2Fwp-content%2Fuploads%2F2016%2F10%2F40M-NVIS-Antenna-1.pdf&usg=AOvVaw1itMvyU5MVsdDqXpl-ye12 https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&c... At higher frequencies (such as the 432 MHz used in this trans-Atlantic contact), the radio waves will not be reflected by the ionosphere and will disperse.