[Towertalk] OPTIMIZED ANTENNA SYSTEM

[David Robbins]

> 
> On Fri, 15 Nov 2002 David Robbins" <k1ttt@arrl.net> writes:
> > Optimum for what? And from where?
> 
> 	My point exactly.  I expect everyone's idea of
> 	optimum depends on their own persepective.
> >
> > For my use I would consider a stack of 6's to be too narrow for
> > contesting from the northeast.  Up here a stack of 4's is probably
> > better to cover more of Europe at one time.  From farther west maybe
> > the 6's would be better as the angular spread to cover Europe for
> > contesting is smaller, or if you are dxing, ragchewing, or handling
> point to
> > point traffic the 6's may be reasonable.
> 
> 	The 6L models on 0.75 WL booms in W2PV's
> 	Yagi Design Book show a -3 dB beamwidth of 50+
> 	degrees.  Is that too narrow from W1?
> 
> 	The 3L models on 0.28 Wl booms show a -3 dB
> 	beamwidth of <70 degrees.

50-60 degrees would be about right.  I'm kind of surprised the pv design
shows that beamwidth though I would expect it to be narrower.  The top
antennas on my 15m and 20m stacks are reoptimized telrex models on 46'
booms that have 5 active elements each(because the element locations are
fixed by the holes in the booms the optimizer detuned one of them on 20m
and 3 on 15m so now they are just there for wind balance).  The 20m one
computer model shows about 50 degree 3db azimuth pattern, but it seems
much narrower and when used by itself is not as good as the 4 element
stack in my opinion.  I see the same effect on 15m but even more so.  I
would guess that part of the difference is probably the elevation angle
that the beamwidth is measured at and height of the antennas. 



David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
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