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Skip Distance and Skip Zone

Skip Distance and Skip ZoneSkip distance(ds) is defined as the minimum distance from a transit antenna that a sky waveat a given frequency will be returned to earth.The frequency must be less than the maximum usable frequency and propagated at its critical angle.

Skip Distance

It can be seen that the distance to where the wave returns to earth moves closer to the transmit antennas the radiation angle increases.When the radiation angle increses (r )exceeds the critical angle (c ), the wave penetrates the ionosphere and escapes earths atmosphere.Skip DistanceAt a distance greater than skip distance, two rays can take different paths and still be returned to same point on earth.The two rays are called the lower ray and the upper ray or Pedersen ray.Pedersan ray is of little significance as it is much weaker than the lower ray and spreads over a larger area .It becomes important when circumstances prevent the lower ray from reaching a particular point.

Skip Distance

The area between where the surface waves are completely dissipated and the point where the first sky wave returns to earth is called Quiet Zone or Skip Zone.Each frequency may have a different skip distance and skip zone.Skip Distance

The figure shows the effect on skip distance of the disappearance of the D and E layers during night time.The level of ionosphere is raised and it allows sky waves to travel higher before being returned to earth.This effect explains that how faraway radio stations are sometimes heard during night hours and cannot be heard during daylight hours.Skip Distance