Pete,
You are not "all wet". You just lack the experience in putting
one of these "monsters" up. Here's the situation:
An 80M Yagi (of any element count) has elements TWICE as long as a
full-size 40M Yagi. That's the basic problem. Elements that are 130-some
feet long
just can't be made "horizontal" and also be able to be put up at heights
over
120 feet high and still be made of reasonable material, be
within the cost of most all of us, and withstand wind/ice, even the
wind/ice in MD!!! It's not a physically realizable objective for
99.9% of us. The other 0.1% of hams who could afford to do this and did
include W3MSK (W3AU), ON4UN, K2GL and a couple others. Antennas, BTW, that
did not stay up very long. (I'm sure we will be told of some that are still
standing!)
So, let's look at today's "reasonable" 80M Yagis. These are the linear
loaded
variety whose element lengths are 2/3rds, or so, the length of a full size
beam.
Linear loading itself adds issues: potential arcing and arc-over, increases
the "height" dimension of the antenna,
and adds wind loading to the shortened element. If the linear loading is
inductive, the antenna is more reasonable
in size (like K1DQV's) and easier to handle. N3HBX has the F12 3 ele 80M
linear loaded Yagi. This antenna has guy struts on each element as well as
on the boom in addition to linear loading wires on each element!!
Add to that the element length is now 85 feet. This is no easy task to
install and keep in the air either.
In my case, I have a F12 EF-180C rotatable dipole. I had to add a
phillistran boom guy to each element half
else it would droop and arc over to the linear loading wires OR droop and
break the linear loading wires. In fact, it did break and that's what caused
me to add the phillistran. I sell a $25 video on the mods I made to this
antenna just to keep it in the air at 149 ft. See: www.erols.com/n3rr
This is after my experience with an EF 180A, a smaller antenna (tip to tip)
but with more linear loading
that was a real "pain" to install. My 80M rotatable dipole experiences span
a period of 4 years with arc-over, breakage, wind damage, broken elements,
element-to-mast clamp insufficiency, etc. You name it, I had it. I had much
experience climbing up/down my tower fixing these antennas.
An 80M Yagi (or rotatable dipole) at 150 feet has special considerations.
That's why compromises such as linear loading
shortened elements need to be considered.
All this to say, Pete, yes, stories abound about 80M rotatable Yagis. They
are legend and will continue to be.
73,
Bill, N3RR
-----Original Message-----
From: owner-towertalk@contesting.com
[mailto:owner-towertalk@contesting.com]On Behalf Of Pete Smith
Sent: Sunday, July 22, 2001 1:52 PM
To: towertalk@contesting.com
Subject: [TowerTalk] 80m Yagis -- Too Tough to Tame?
Yesterday I visited a big new multiop station, and was able to be a fly on
the wall during discussions among a number of experienced, big-station
builders. Almost without exception, they seemed seriously daunted by the
idea of trying to install and maintain an 80m yagi, even one less than full
size, and even in our relatively benign climate. The air was full of tales
of antennas that lasted three weeks or less, and costly failures
I freely admit my lack of experience with these beasts, but I don't get it.
Why should design of mechanically durable 80-meter loaded yagis be that
much tougher than, for example, a full-size 40M yagi of equivalent element
count? Surely, the mechanical design software currently available can tell
you what to do to make a75%-scale 80m yagi survive 80, or 90, or 100 MPH
winds. I understand that cost is a factor, but once you buy the hardware,
why shouldn't you be able to have a mechanical failure rate comparable to
that experienced with other yagis?
My suspicion is that the hardware probably needs to be beefier than most
people's intuition and judgment usually tell them, and that failures
probably result in some part from not working the design problem hard
enough to start with.
Am I all wet?
73, Pete N4ZR
No, no ... that's WEST Virginia
List Sponsor: Are you thinking about installing a tower this summer? Call us
for information on our fabulous Trylon Titan self-supporting towers - up to
96-feet for less than $2000! at 888-833-3104 <A
HREF="http://www.ChampionRadio.com";>
www.ChampionRadio.com</A>
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
List Sponsor: Are you thinking about installing a tower this summer? Call us
for information on our fabulous Trylon Titan self-supporting towers - up to
96-feet for less than $2000! at 888-833-3104 <A
HREF="http://www.ChampionRadio.com";>
www.ChampionRadio.com</A>
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|