Guys,
No problem if you've got the skills and the money. Look at the full
sized 3 element yagi from DJ6JC in the ON4UN Low Band DXING handbook.
The elements weigh only about 250 pounds each and are mostly made of
tapered tower sections. The elements sag only 1'. It is designed for
106 mph.
You tune the elements by suspending them from a 125' crane.
By the way, the resonant frequency of the elements changed 600Khz from
just above ground to 125'
73 de Brian/K3KO
Bill Hider wrote:
>
> 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
>
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