http://g7rau.co.uk/soft/downloads/sporadic_e.pdf
http://www.g7rau.co.uk/default.aspx?menu=21001
http://www.dk5ya.de/
https://www.antennex.com/prop/prop0806/prop0806.pdf
http://www.wia.org.au/members/armag/2012/april/documents/HarrisonEsPt1.pdf
http://www.vklogger.com/forum/viewtopic.php?f=43&t=9832
chordal hop - a hop with two or more consecutive ionospheric reflections from the same layer
http://www.g7rau.co.uk/default.aspx?menu=21001
http://www.dk5ya.de/
https://www.antennex.com/prop/prop0806/prop0806.pdf
http://www.wia.org.au/members/armag/2012/april/documents/HarrisonEsPt1.pdf
http://www.vklogger.com/forum/viewtopic.php?f=43&t=9832
chordal hop - a hop with two or more consecutive ionospheric reflections from the same layer