Ionogram is chart  X axle is  Frequency  , Y axle is  height of reflection ( ionosphere height )

I understand this chart is   reflection from ionosphere sending radio wave vertical up.  so if sending angle is not vertical reflection does extend more to higher frequency.  But, it is good reference  for Ham to see if band is open or not.


LINK to Point Arguello , CA, USA   data

there are  many place which takes this data through out the world

click this link for lists

click this link for world wide map


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