[CQ-Contest] Be careful
btippett at alum.mit.edu
Sun Jan 2 18:12:25 EST 2005
>And how much extra effort is involved in installing a "small 3-stack" vs.
verticals? Particularly in a DX-pedition setting?
Answer: a LOT more effort.
>Is that worth less than an S-unit?
Answer: more like 2 S-units (11.7 dBi).
Gain Summary (NEC-2, HFTA, YO7, etc.):
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
This thread began with a few blanket statements by Yuri:
>Verticals on the beach will outdo Yagis at low angles and DX performance.
I have played with them as N2EE on 10m from Cape Hatteras (US LP record), NC
and can vouch for it. Now using some real arrays....
>Just to bring to attention that verticals can be awesom, beat Yagis when
properly used (on salty beaches).
These statements are not necessarily true, either theoretically
or in real world results. As K2KW and I both stated, a verticalarray's
advantage improves as you go down in frequency, mainly
because stacked Yagi systems are more difficult to implement there.
There is no doubt in my mind vertical arrays are the best choice for
portable operations on salt water, but let's not kid ourselves that
they are ALWAYS better than Yagi stacks.
73, Bill W4ZV
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