On 4/22/2012 8:54 AM, Pete Smith wrote:
> I'm a little uncomfortable with the very small bend radius of the coax
> in that setup. With foam-insulated coax that could risk a short from
> the center conductor to the shield.
The bend radius does not exceed the spec for the coax. OTOH you will
notice the choke hangs a good foot below the feed point. That is enough
coax to replace the termination at least 2 or 3 times if it proves
necessary. I currently run the legal limit well off resonance which
presents a very high voltage at the nodes. running the loop around a
piece of plastic tubing (cut in half lengthwise) or formed plexiglass
would eliminate much of that stress, but I wanted/needed to keep the
weight of the unit as low as possible with the coax coming out near the
center as the antenna is already supporting nearly 100 feet of RG8 size
coax in addition to the center connector and current balun. I could
replace the Davis BuryFlex(TM) with LMR-400 which is notably lighter,
but then I'd be adding two UHF connectors, plus weather proofing, that
would be supporting the entire length of coax. I said two connectors as
I'd use one male (PL-259) and one female(?) for which I've forgotten the
nomenclature. I'd do that instead of two PL259s and a double female
connector with the additional weather proofing. That feed line hangs
down from the feed point and curves back to the tower where it's
attached at roughly the 20 foot level. There is another current balun at
that point. There is a pulley at the tower with a rope through it to
second relatively large pulley that the coax runs through, that lets me
raise the coax up the side of the tower. The upper end of the antenna
is held by a rope through a pulley near the top of the tower which
allows me to raise *and* lower the antenna in 5 minutes or less.
BTW I put 4 tiny dabs of super glue between each of the the 2.4" cores
so the stack of 5 is rigidly glued together. With a little heat and
force they come apart relatively easy, but I've never had one fail on a
hot, windy, summer day.
There's not a lot of flexing in the coax even on windy days except where
it runs through the pulley, but that is only when raising and lowering
it and that does not exceed the "repeatable bend radius" for LMR-400 so
it's well within spec. The wind is currently gusting over 20 mph and I
can just barely see the feed point or the coax back to the tower move.
Like most things this is a compromise.
> 73, Pete N4ZR
> On 4/21/2012 11:20 PM, Bob K6UJ wrote:
>> Looks nice and secure Roger.
>> I like the idea of eliminating a PL-259/SO-239 connection.
>> On Apr 21, 2012, at 7:07 PM, K8RI wrote:
>>> On 4/21/2012 6:17 PM, Dick wrote:
>>>> I just got a rope over a tree after 4 years of trying. I need a dipole
>>>> center insulator that has strain relief for the coax. To clear the
>>>> branches, the coax will be pulling against the center support rope. All
>>>> the center insulators I've seen have an SO-239, it doesn't seem like
>>>> putting that strain on a PL-259 is a good idea... Do any have a strain
>>> This is not center supported, but it does support the coax and current
>>> balun from the feed point.
>>> The ends of the wire need a little trimming but this is what I have:
>>> http://www.rogerhalstead.com/ham_files/AntennaFeed1.htm 5 #31 cores and
>>> 6 turns of Davis BuryFlex(TM)
>>> Roger (K8RI)
>>>> Dick NY1E
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