"The HF band used in aviation ranges from 2 to 22 MHZ. Different frequencies have different range capabilities; i.e., the higher the frequency the greater is its range. Therefore, frequency is chosen by the pilot to meet the range between the transmitting and reception points, and the ground station will monitor a range of frequencies because personnel are unsure of the exact distance to the aircraft. This is also the reason why you can be received by a station 2000 nautical miles away but not by a station only 500 nautical miles away."
Why do the higher frequencies in the HF range travel further then the low frequencies in the HF range?
Why can you receive a station 2000 nautical miles away but not 500 miles away, would it be because the station at 500 nautical miles away is using too low A HF? and 2000 using the correct high frequency i.e. high?