[CQ-Contest] Re: [TowerTalk] 4-Square Owners & Experts "& resonant trees..."

[i4jmy at migate.ampr.org]

  A vertical antenna can be either a good or a bad radiator, the
  concept is quite relative, it depends....  
  
  First of all, the common assumption that a vertical antenna is a 
  low angle radiator is often unrealized because of refractions 
  and reflections of ground.
  A vertical antenna can be a low angle radiator but often it is
  not true.
  
  The image antenna of a vertical, is theorically in phase with the
  real antenna. The consequence is that at 0 degrees of radiation 
  angle, there should be a 3DB gain (maximum).
  
  A zero degrees radiation only says that verticals are potentially 
  good antennas to produce more ground ground wave than horizontal
  ones. More gain at proper angles is another story, at least for DX 
  and sky wave propagation.
  Now, in the real life I mean, a vertical antenna is effectively a 
  low angle radiator only when the pseudo Brewster angle is quite low, 
  some unity, but this happens only over sea water and other extremely 
  good grounds.
  
  Below the brewster angle, the image antenna phase reverses, and
  there is rather a cancellation than a sum in the radiated energy !
  
  Moreover, the "very good ground" to be effective, must extend for 
  a large area (just below the antenna it's not enough) and this makes
  vertical antennas performance mostly depending on enviromental 
  situation ( the location ).
  
  Luckily, HF propagation in the low bands doesn't require so low
  angles (the 1 or 2 deg of 10 meters are totally useless), and even 
  an imperfect ground (i.e. producing a pseudo brewster of some 10deg) 
  doesn't prohibit the vertical from radiating effectively for DX
  and sky wave traffic (above Brewster)
  
  However, an horizontal antenna at a reasonable height from ground, 
  can offer as much as 6DB of gain for some angles, and with a much 
  lower dependency by ground characteristics.
  
  Here it cames the reality that for the typical wave angles of
  160 80 and 40 meters, an horizontal antenna placed at reasonable
  height from ground can outperform a vertical array in gain (the
  directivity and immunity to high angle signals of a phased array is 
  a different story) and, in the near of slooping grounds or other 
  discontinuities could "beat" a vertical antenna up to some 12 DB.

  Personally I noticed 10DB gain on 80meters when replaced a 4 half
  wave verticals (dipoles) phased array, in favour of a 2 phased 
  horizontal dipoles at 150 feet from ground.


  73, Mauri I4JMY (one of IR4T)



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