HF Comms (skip Distance) RNAV

The minimum skip distance is the shortest distance that the skywaves of HFHF —1) Radio Waves: High Frequency2) Human Performance: Human Factors comms will travel - in other words, you are able to reach anyone beyond that point with a wave, but not anyone closer. It therefore pays if the minimum skip distance is as short as possible.

There are two main factors that affect this skip distance.

1. Frequency of the wave. If the frequency is lower, then that will result in more bending (refraction) meaning the signal gets back to earth sooner. This is a good thing, but unfortunately means more static and a less clear signal.
2. Height of the ionosphere. The sooner the wave is bent back towards the earth, the shorter the minimum skip distance, so a lower ionosphere (which happens by day) gives the shortest minimum skip distance. A useful way to remember this is "sun down, frequency down". At night the ionosphere is higher, so you have to increase the amount of bending (by reducing the frequency) to compensate.