[TowerTalk] Phasing verticals and stubs
jimlux at earthlink.net
Wed Apr 5 15:59:55 EDT 2006
At 10:58 AM 4/5/2006, Bill wrote:
>What you are describing sounds like simply two 2-antenna systems placed 90
>degrees to each other where on of the antennas is common to both. I
>conclude that from your statement that there are 4 directions available. On
>that basis the directionality of the systems is a cardioid pattern which has
>a 120 degree wide lobe at the half power points.
Depends on the spacing of the antennas. If they are closer than 1/4
wavelength, then you can get a very narrow beam with fairly high gain.
Think of a W8JK turned on it's side. There are, of course, the usual IR
loss issues with this sort of thing, and for verticals, where half the
element is "soil" or "ground radials", it might be even worse.
>I have not seen the pattern for the equilateral array but based on the
>materials I have seen, that pattern has a 60 degree wide lobe, so it is
>hard to believe that the gain difference is only 0.2dB. The cardioid
>pattern is indeed directional, hence the use for many years in the
>non-directional beacon system for aircraft (relying in that case on the null
>in the opposite direction). However the forward gain is rather modest. The
>formula for that pattern is (1+coswt) which translates to 2.0 where wt=0
>degrees and 0 where wt=180 degrees. Thus the front to back is very good but
>the forward gain is just modest.
The formula you give is for elements "some distance" apart. Consider, as
an example, a pair of elements 1/10th wavelength apart, phased 180 degrees
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