[TowerTalk] Coils vs Linear loading on 80M yagi

[Charlie Summers]

Folks,

There has been a long thread about coils Vs linear loading on lower
frequency yagis.  I think it is too bad that the impracticalities of having
an A/B switch for the larger yagis makes actual testing a bit of a pain and
rules out all but the most exotic stations from even thinking about this.
However there are several good hints that one has when a yagi works or
doesn't work and so I would like to relate an anecdotal story here because I
believe it has some merit.

I ordered a 80M yagi.  It came with linear loading wires.  The instructions
indicated I should set the director to resonate at such and such a frequency
and the reflector at such and such and tune the driver and fire away.  This
approach left a lot to be desired because I really didn't know where the
heck the parameters of this beam set the pattern or the max front to back.
It was just impossible to tune properly.  I really didn't get much help from
the factory on this either so it turned out to be a case of what you see is
what you get and enjoy.

However there was a larger problem lurking in the woods.  Those linear
loading wires whipped around so in the wind that the yagi was essentially
unusable in even a small breeze.  The elements swaying in the breeze caused
the loading to vary.  It also caused the pattern to change.  It also caused
some other things like fatigue of the elements causing one section to
slightly rotate back and forth wearing the individual fasteners between
element tubes so that eventually a black dust appeared at each element
joint.

The linear loading wires were anchored at the boom approximately two feet
above the boom meaning they went from way out on my 88 foot elements to a
point two feet above the boom.  This introduced a vertical component into
each element making the yagi extremely noisy.

To summarize, it had little front to back and little gain in actual use.  In
a wind, I had to QSY to another band.  This happened not only on my 80M yagi
but also on a 30M yagi using the same linear loading scheme and happened on
my two neighbors 40M yagis which were designed the same.

I pointed this out to the factory but received little help in a solution
other than promises to check into it.  After a rather prolonged wait for a
factory input I started to look elsewhere.  Rumors had abounded about a new
approach to 80M yagis and armed with this information I contacted W6ANR.
Dave was quite optimistic he could fix my yagi but it would involve somewhat
of an extended schedule because between Dave and Rich, K7ZV who made the
coils, there were several conversions ahead of me.  Having nothing to lose I
waited and one day, a box of coils showed up on my doorstep.

I immediately started to work by totally rebuilding my yagi.  I added 8 feet
to either end of the boom bringing it to 62 feet.  A second overhead truss
assured me of adequate guying.  I added the coils into each element and
eliminated those fussy linear loading wires, instead replacing them with
Phyllistran overhead guys.  Tuning was a snap because one could actual
feather the pattern to the area it was desired.  Dave, W6ANR, would feed me
dimensional changes based on my measurements with a yagi on another tower
but much higher than my 80.  Now, thanks to Dave and Rich, K7ZV, I have a
yagi that really plays.  And another nice part about this project was when I
needed help, I got it NOW!

If you doubt the efficiency of this design listen some time in an 80M
pileup.  The guys who really rule the roost use those W6ANR converted beams.
They are all over the west coast, some in the interior of the States and
some in Europe.  The design is practical, tuning is a snap and results are,
well fantastic!

I don't own any interest in Dave's or Rich's venture. I am just a satisfied
user.  This conversion was written up in detail in K0CS's Low Band Monitor
in which I do not have an interest either.  If you want to see that article,
contact lance@diac.com for a back issue.  I do have a few photos I can send
digitally to anyone who requests them direct.

My yagi is on top of a hill with lots of falloff in all directions.  It is
on a 89 foot motorized crankup which allows me to bring the antenna to me
instead of me going to it.

73,

Charlie, W0YG..>>




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