--- W0UN -- John Brosnahan <shr@medinaec.com> wrote:
> Scott--
>
> Sounds like you are getting lots of good advice.
>
> I had a stack of two of the 4L40M KLMs stacked with
> four TH7s. Two of the TH7s were within 5 ft of
> their respective KLMs. Never had the tribanders
> affect the KLMs in any way. Although the KLMs did
> bother 15M on the tribanders.
>
> I think the most likely scenario is something shorted
> in the feed system. The crossed-over phasing lines
> are the most vulnerable. When the boom is bowed up
> slightly by the top guy the phasing lines can short to
> each other or to the boom.
Alright - I think K4JNY and I have a place to start,
though it's going to be Jeff up at the top of the tower
figuring out the answer to this riddle once we have the
chance to look at it again in a few weeks.
> I ended up using some light dielectric rope to help
> support the phasing lines above the boom. If you
> pull the driven elements far enough apart to put
> significant tension on the phasing lines to keep them
> apart you are likely to pull out the ends of the phasing
> lines when the boom bounces in the wind. The
> phasing lines can just fail at the connection holes.
> Best to keep them somewhat loose and support
> them with their own little top rope.
Interesting - we didn't try supporting them, though there
is the opportunity to do so. I see this in your original
notes but as we had added PVC spacers and didn't see any
shorting problems, we didn't add a support rope. I wonder
about the 'too tight' issue - we felt they were awfully
loose, to the point of shorting to the boom, when we built
it with the stock spacers.
> Of course my stack of 4L40M antennas was
> mounted on the face of Rohn 55 using 10" aluminum
> channel and the channel added some unique problems
> in clearing the mount with the phasing lines.
>
> Good luck--and if you have a digital copy of my
> 4L40M notes you might send them to me--I seem to
> have lost them in the move to TX. They are probably
> on some computer--but I have about 20 here and
> some are in storage. And since you mentioned my
> call, someone is bound to write! ;-) And I can
> probably add some more details now.
We used what you typed for the benefit of TowerTalk
on 9/7/02. It's located at URL
http://lists.contesting.com/_towertalk/2002-September/050513.html
We also added a side-to-side truss to keep side movement of
the antenna to a minimum, consisting of a 6 foot pipe bolted under the
boom perpendicular and then a diamond made out of Phillystran to try
and stop side-to-side movement of the antenna.
To say the least, I am really familiar with this antenna now. Over
Memorial Day weekend and the following weekend I essentially built this
antenna in K4JNY's front yard by myself, with Jeff adding the side
truss, mast hardware, and top boom support guy (also Phillystran).
We did everything you suggested - we bought DX engineering hardware,
nylon self locking SS hardware, pinned all the element pieces with
sheet metal screws, milled out the centers of the linear support
brackets - everything.
> BTW I have FOUR of them now. Two in boxes and
> two still up in CO. Both in CO have finally shown
> a failure--and the same failure. A tip on one half-element
> has pulled out. But the tip is still being held in the
> air by the linear loading. I suggest pinning the
> elements if you don't want this to happen. But I got
> about 10 years out of them without ANY of the
> well known failure modes by using my minor mods.
Yup - and I expect that this one will do the same. After the
all day battle that it took myself, K4JNY, N4CM, and
KD4HIK to get it up the tower and mounted, about the last
thing we want to do is take it back down.
> Think the mods must work! Still need to take the
> two down in CO--or talk Duffy out of his! You can
> bet I will pin the element sections in the future.
>
> 73 es gl John W0UN
Thanks - once we get an answer to this, I'll post it.
Scott W4PA
=====
Always been the radio's child
Quick-to-smile precious baby
Search the dial and electrify
--Widespread Panic "Radio Child"
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