It is important to note Brians table of gain figures and the conclusions
reached: I would not argue with any of his points except minor issues
about location and the reality of cost per S unit. The conclusions leave
out those of us in the central U.S.. Most hams don't have the benefit of
living "on the beach" within 120 miles of the Atlantic Ocean. We really
have to work for every S unit to get through the pile up of folks on the
east coast. Of course the west coast has different advantages and
disadvantages for contesting.
The table illustrates clearly that it is VERY difficult to get a fraction
of an S unit improvement on 80/75 meters. From the central U.S. we need to
be much closer to a 12 degree angle of primary lobe or we simply aren't in
the contest (staying with Brians Illustration of EU sigs) until after the
pile-up dies down, or better yet we use operating skill and courtesy to
make the contact!
We simply can't do it by raising an 80M dipole 20 feet, or adding an extra
element until we get into spending vast amounts of money to get to at least
125 feet (depending on ground conditions as Brian notes). So we get to the
magic height (as close as we can) with wires. And as all of us remember
who were hams before the technological revolution in the 1980's--- Wire
antennas get the job done when thought out and installed properly. Toms
post about wire is an excellent example.
Ham radio is a great hobby, isn't it? HF is where we can still compete
with monster arrays by using wire and inventive installation
techniques. Most of all operator skill and patience. It is wonderful to
read about the big dollar monster contest station arrays. God bless you if
you help advance the hobby by experimenting with stacked 80 meter yagis or
whatever floats your boat. Reality dictates to most of us that we compromise.
So on behalf of all of us with dreams of contesting with a 3 element 80
meter yagi on top of a 200 foot tower---then the stacks for each band that
would naturally accompany that installation lower down the tower---I thank
Tom and Brian and the rest of you for contributing to this
discussion. It's great to enjoy those beams vicariously, even though our
fence needs to go up, then the central air.....on and on.
73,
Frank, KB8XU
At 12:24 PM 7/23/2001 +0000, Brian K3KO wrote and referenced Tom N4KG:
>Here are some EZNEC calcs of an 80 meter dipole at heights from 60' to
>160'
>
>Clearly guys who get even dipoles high win.
>
>height max gain/angle half power angles 20deg gain
>60' 6.52dbi/89deg 30deg 1.5dbi
>80' 6.16dbi/52deg 23deg 2.16dbi
>100' 6.38dbi/40deg 19,81deg 3.4dbi
>120' 7.05dbi/33deg 16,56deg 5.0dbi
>140' 7.84dbi/28deg 14,45 6.8dbi
>160' 8.31dbi/25deg 12,39 8.3dbi
>
>The 20 degree angle point was chosen because it represents a point
>that the a point in the second peak of the eu arrival angle
>distribution with a large fraction of the total . (East coast,
>Washington DC) It says going from 80' to 160' one gains about an S
>unit in EU from the East coast.
>
>The 6-12 degree region contains the first arrival angle distribution
>peak. It takes a dipole at 160' to put much energy there. A vertical
>isn't the answer to cover these lower angles -- unless you have
>excellent ground conductivity. EZNEC shows that verticals are also
>poor performers at these angles there in areas of conductivities in
>the 2-5 range (my QTH is 2.5.) Of course, if your vertical antenna is
>on a salt marsh, you win.
>
>73 de Brian/K3KO
>n4kg@juno.com wrote:
> >
> > I would not expect much benefit from a 2L80 at only 85 ft
> > which is barely over 1/4 WL high. The ground reflection at
> > 1/4 WL high is centered straight up. The free space pattern
> > of the Yagi is centered at the horizon. The vector product
> > will peak somewhere in between. You may want to model
> > a 2L80 and an 80M dipole at 140 ft and 85 ft and see how
> > much net gain you will realize from that configuration before
> > proceeding. You might be surprised to see little benefit
> > over a dipole at 85 ft.
> >
> > 40M antennas play VERY WELL from 70 to 100 ft so that
> > is a good choice.
> >
> > Tom N4KG
> >
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