Bob
Seems to me, this the heavier duty truss I suggested and installed at your
place. Glad it continues to deliver!
Regards,
Mark, K1RX
> On Oct 7, 2021, at 8:23 PM, kq2m@kq2m.com wrote:
>
>
> I have three LJ205CA's (HG205CA's) on my 130' tower. They were all put up in
> late 2008 - so 13 years ago. They have been through and survived three EF0
> and EF1 tornados, one macroburst, two Hurricanes (Hurricane Sandy had wind
> gusts of 110+ mph) and countless ice storms and vicious T-storms with
> hurricane force wind gusts. I am convinced that the only reason they have
> stayed in one piece is due to the Trusses that I constructed and the fact
> that I balanced the antenna at the Boom to Mast Clamp of the antenna by
> bolting lead sheeting inside the boom after the Truss was in place and both
> ends of the boom were guyed with kevlar rope to the Truss. With the balance
> point at the clamp where the antenna attaches to the mast, there is less
> stress on the antenna and clamps hopefully prolonging its survival.
>
> I cut a 3' length of steel pipe to be used as the Truss Mast which is bolted
> to the antenna boom, and in the case of the 5L at 130', it is also bolted to
> the rotator mast, essentially forming a rectangle of pipe bolted to the Truss
> and antenna greatly reducing the potential back and forth movement of the
> antenna in the boom to mast clamp during strong winds. Before I did this the
> stock boom to mast clamp would get torn to shreds by the rocking motion in
> the wind within 1 - 2 years and needed to be replaced. Now the antenna is
> happy and the boom to mast clamp looks unscathed after many years.
>
> Bolted at the top of the Truss mast, I have a 4" x 4" thick aluminum plate
> which has on each side a large turnbuckle to which kevlar rope is attached
> tightly with three saddle clamps with the other end through an Eyebolt that
> is bolted above and below the boom and also which is also attached tightly
> with three saddle clamps. The same thing is done on both sides of the
> antenna. Each eyebolt is bolted through both sides of the boom approximately
> 1' from the end of the boom for maximum support. The turnbuckle easily allows
> me to tension the Truss wires (kevlar rope) and make adjustments to the
> antenna for sag while it is on the tower.
>
> The Truss is the only reason that these antennas have survived despite the
> winds being so fierce at my qth that the top 20 @ 130' has had several
> element tips bent UP while the other side of the antenna has element tips
> bent DOWN! (Thanks to the August 4th tornado last Summer).
>
> BTW, I didn't read the manual regarding how to build the Truss or where to
> attach the Truss ropes to the boom. I wanted to design something better and
> heavier duty for my qth which gets extremely severe wind weather on a regular
> basis.
>
>
> 73
>
> Bob, KQ2M
>
>
>> On 2021-10-06 15:12, Mark - N5OT wrote:
>> "When all else fails read the instructions."
>> (ask me how I know this :-)
>> 73 - Mark N5OT
>>> On 10/5/2021 10:38 AM, Ed Williams wrote:
>>> The manual I have on the LJ205BA states the boom support should be approx 3'
>>> above the boom and 16'4" from the boom support clamp. I hope this will help.
>>> 73, de KN4KL ed
>>> -----Original Message-----
>>> From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
>>> john@kk9a.com
>>> Sent: Tuesday, October 05, 2021 11:02 AM
>>> To: towertalk@contesting.com
>>> Subject: Re: [TowerTalk] height of truss for converted HiGain LJ205
>>> I concur with Grant, I connect the boom truss on my homebrew Yagi's about
>>> 2/3 out. This is approximate as I try to maintain symmetry while also
>>> avoiding any elements. I use DX Engineering ATBB-3 boom brackets, I do not
>>> use Big Grips due to their size.
>>> John KK9A
>>> Grant Saviers KZ1W wrote:
>>> Jeff,
>>> The number of variables (and equations) is pretty large - and Leeson
>>> enumerates these in his equations:
>>> guy angle
>>> section moments & lengths
>>> boom slenderness
>>> guy angle to boom
>>> attachment point
>>> guy spring constant
>>> boom moment
>>> Perhaps it defies "rule of thumb". However, it seems to me that
>>> depending on the boom, somewhere around 2/3 out from mast for the guy
>>> attach point is sensible. All depends on the taper/section moments. Guy
>>> to boom angle of 20 to 30 degrees. My preferred very long boom/element
>>> design is two guys each side to a single cross member on the mast about
>>> 24" each side (48" overall). This yields lateral wind support as well as
>>> ice strength and sag reduction. Did this for a rebuilt 86ft 80m loaded
>>> rotatable dipole. Some serious ice and wind over 10 years and still in
>>> one piece at 100ft up. Leeson recommends 3 guys, two below the boom to
>>> counteract wind lift and one above. Clearly needed for his QTH wind
>>> conditions.
>>> With larger angles of guy to boom, negative sag to the guy attach point
>>> is possible without overstressing a slender column boom into buckling.
>>> My 10m 5L 24ft booms are 3" diameter and are guyed, but the single guys
>>> are not symmetrical since the boom mounting point is on rings and space
>>> between elements is needed for tower clearance. The guy angle to boom
>>> is pretty near 30 deg. Probably total overkill considering the 3" boom.
>>> One error (I suspect) in my construction was using guy grips on the
>>> Phillystran at the boom attach points. I suspect they are long enough
>>> conductors to affect the performance. Not modeled though. A problem
>>> unique to 10 and maybe 12m. Wire rope clips are ok on the smallest
>>> Philly if thoroughly tightened and I have seen Nicopress compression
>>> sleeves used successfully. Nicopress will be the fix (someday).
>>> Grant KZ1W
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