On 9/27/2012 4:58 PM, W2XJ wrote:
The other difference is that all this information is based on ground wave propagation. There is nothing that addresses higher angle sky wave propagation common for 160 M operation.
More correctly, it is field strength measured close enough to the antenna to be "stable."
The vertical pattern is primarily shaped by soil conductivity, and is the result of energy radiated by the antenna being reflected by the earth in the FAR field of the antenna.That reflection adds to the direct radiation to form the vertical pattern .The stronger the reflection, the greater the low angle radiation.
The "ground system," whether a ground screen or radials, is in the NEAR field, and affects how much power is lost in the earth, how much is left to get radiated so that it CAN be reflected. In other words, the ground system primarily affects the overall STRENGH of the signal, but has very little effect on the shape of the vertical pattern.
73, Jim K9YC _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
