Dick Green WC1M wrote:
> K8RI wrote:
>> Use sufficient tension on the cable clamps, but not enough to damage the
>> Don't crank the nuts down tight like you would on steel cable.
> Generally good advice, and of course you don't want to damage the
> Phillystran, but in the case of the 4-el SteppIR boom support, I would
> advise cranking the nuts as tight as you can by hand.
It's a balancing act. I'd certainly go tighter than "hand tight" and
use a wrench or preferably nut driver to "snug them up"
*Generally* there isn't a lot of load on the boom truss except with the
really BIG monobanders.The truss broke on my 30' long, 7-L 6-meter Yagi
some 4 or 5 years ago. It's gone through two ice storms since without
it. Just clamping the truss under the saddle clamp is a short cut.
Me? I'd take a piece of Aluminum angle bout 1/8" thick the same length
of the saddle clamp width, drill two holes for the U-bolt in the saddle
clamp and one on the other side centered between the bolts holes (IE 90
degrees to the saddle) and install an eye bolt. The thimble for the
truss can fit directly into the eye, or a good S-hook can be used IF
there is enough tension to keep it from coming out in high winds. If
the manufacturer took the route of just clamping the truss under the
saddle I'd think of poor engineering practice (and a rather inelegant
way to fasten it) even if it is sufficient to hold.
> The reason I say this
> is that I didn't do so on one of the 4-el SteppIRs in my 3-stack, and the
> boom support pulled out of the clamp. So the antenna was without support on
> half the boom. Unfortunately, the end that slipped out was the one attached
> to the boom and was consequently out of reach from the tower. It was the top
> antenna, so I wasn't crazy about the idea of tramming it down to fix the
> boom truss.
> I contacted K7IR at SteppIR about it, and he told me that the boom is way
> overdesigned and the truss is there mostly for cosmetic reasons. So I left
> it that way for months, until I had another reason to take that antenna down
> (the second director motor had, unbeknownst to me, been damaged by that end
> of the antenna being dropped hard on the ground during installation.)
> Later, I spoke with K1DG, who had exactly the same experience with the boom
> truss on one of his 4-el SteppIRs. He devised an ingenious repair method
> whereby he used a snap hook attached to a fishing pole to snag the eyelet on
> the boom end of the truss. So, if it lets go you can repair it, but not
> without some difficulty.
> Of course, if you're one of the many SteppIR owners with a tilt-over crankup
> tower, my advice may not apply.
> 73, Dick WC1M
>> -----Original Message-----
>> From: Roger (K8RI) [mailto:K8RI-on-TowerTalk@tm.net]
>> Sent: Friday, October 30, 2009 1:01 AM
>> To: email@example.com
>> Cc: towertalk reflector
>> Subject: Re: [TowerTalk] Phillystran damaged?
>> Mike wrote:
>>> My 4L SteppIR uses small diameter Phillystran as a bridle for the boom,
>>> clamped with saddle clamps. I have the antenna on the ground, and was
>>> going to replace the saddle clamps with stainless steel ones.
>>> When I took off the old clamps, the 'stran is crushed absolutely flat
>>> where the U-bolt side bore on it. It appears as tho there is nothing in
>>> the jacket. The jacket isn't broken, only flat.
>>> Is the Philly cut or broken, or is that much crush normal? It doesn't
>>> seem like a good idea to breach the jacket to have a look-see.
>> The core of Phillystran is Kevlar (IIRC) and is made up of many fine
>> strands. When clamped that allows the jacket to flatten or distort
>> considerably without a great deal of loss in strength. OTOH any time
>> you flatten a cable it loses some strength that varies widely between
>> materials. The black jacket is purely weather proofing as Kevlar is
>> affected by water and Ultraviolet light.
>> Using saddle clamps doesn't sound like a good way to attach the boom
>> truss if the cable is just placed under either the U-bolt or saddle. I'm
>> assuming you are using the small (1200# test) cable. That is normally
>> terminated by using a thimble and three cable clamps. Use sufficient
>> tension on the cable clamps, but not enough to damage the Phillystran.
>> Don't crank the nuts down tight like you would on steel cable. Proper
>> tension on the clamps will still noticeably distorte the cable. That's
>> why they use 3 with less tension instead of 1 or 2 that are tightened
>> down more. Remember the U-bolt" clamps on the "dead side" while the
>> saddle clamps on the side with tension.
>> Roger (K8RI)
>>> 73, Mike NF4L
>>> TowerTalk mailing list
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