[BC] Ground system

[Cowboy]

On Saturday 11 February 2012 02:23:40 pm Richard Fry wrote:
> But all of the useful, far-field radiation from a vertical monopole 
> originates from the vertical section only, not from buried (or elevated) 
> horizontal radials.

 Correct, the operative word being "useful."

 If we assume a portion of the wave such that all of the current
 fed at the moment, is moving away from the feed point in the
 vertical section, and therefore toward the feed point in all of
 the "ground" section....

 To an observer at some distant point, the current in the vertical
 section radiates a signal.
 The current in the "ground system" does not radiate.
 However, it can be acknowledged that since all of the current
 in the ground system section is all flowing toward the feed point,
 then the left hand section does radiate a signal, of equal amplitude
 to that in the right hand section.
 To our distant observer, those currents are flowing in opposite
 directions. One flowing to the right, and one flowing to the left.
 Therefore, the field radiated by each is canceled by the other at
 the point of our observer, and is therefore said that the ground
 system radiates no useful far field energy.
 Additionally, this energy not radiated is perpendicular to that
 radiated by the vertical section.

 To an observer standing on the ground system, proximity is a very
 important aspect, so the energy radiated by the radial under his
 feet is not completely canceled by the energy radiated from the
 complimentary radial some distance away, on the other side
 of the tower, and so does produce "useful" near field energy
 at the point of our observer.
 As such, one can find broken radials by walking the ground system,
 and finding anomalies in the radiation which can not be directly 
 detected at any distant point.
 This is solely due the close proximity, and therefore greater
 amplitude, of the energy radiated in the immediate vicinity
 of the detector.

 Ain't physics fun ?
 ;)


-- 
Cowboy