[CQ-Contest] Be careful

[kk9a at arrl.net]

Bill, your gain figures seem to favor the yagi(s), but if the gain is not at
the desired radiation angle it's useless.  For example your single 6el Yagi
(if 1W.L. high) has a radiation angle of 14 degrees.  Depending on
conditions the optimum angles for 10m can be much lower.  The verticals over
salt water have a very low radiation angle and likely beat the yagi at 5
degrees.  They also don't have the lobes that a horizontal antenna has so
there's no angles that are not covered.   I've played with a simple two
element 40m parasitic beach vertical array as ZF2JB and I was impress with
the performance.

BTW, I wouldn't call a 105' 6/6/6 as a small stack - especially when
comparing it to a few 8' whips in the sand.

John KK9A


From: Bill Tippett <btippett at alum.mit.edu>
Date: Sun, 02 Jan 2005 18:12:25 -0500
List-post: mailto:cq-contest at contesting.com



1.  Single 4-square over salt water = 10.2 dBi
2.  Four phased 4-squares over salt water = ~16 dBi
(I suggested this option just to show what kind of vertical
array it would take to be more competitive with a Yagi stack).
3.  Single 6 el Yagi over average ground = 16.7 dBi
(10.7 antenna + 6 ground reflection, TOA depends on height)
4.  Dual 6 el Yagis over average ground = ~20 dBi
5.  Triple 6 el Yagis over average ground = 21.7 dBi


BOTTOM LINE:  On 10 meters, a single 4-square over salt
water will only beat a dual stack of Yagis only at TOA's
below 3 degrees, which represents only about 15% of the
W4>EU propagation statistics according to HFTA.  Its
advantage is a single broad lobe covering a wide range
of TOA's, but it cannot compete with a switchable stack
which can be focused on particular TOA's as conditions
change.  Someone asked about a Yagi over salt water...
HFTA shows virtually no difference between salt water
and very poor grounds.  You should ask N6BV why that is
but it may because the incident angles are small enough
that ground gain is achieved independent of conductivity
differences.