Sorry wrong thread.
On Tue, Aug 14, 2018 at 10:52 AM, Joe Partlow <joe.w6jwp@gmail.com> wrote:
> I cheat: http://ac6v.com/swrmeter.html
>
>
> On Tue, Aug 14, 2018 at 9:56 AM, Jim Thomson <jim.thom@telus.net> wrote:
>
>> Date: Mon, 13 Aug 2018 16:40:04 -0700 (PDT)
>> From: terry burge <ki7m@comcast.net>
>> To: TowerTalk@contesting.com, terry burge <ki7m@comcast.net>
>> Subject: [TowerTalk] supporting a 40 meter rotatable dipole with
>> trusses
>>
>> <Been working on my 40 meter rotatable dipole I plan to put up at 124
>> feet or so. But I'm worried about making sure whatever I come up with to
>> fix the 3/16" dacron truss lines to the elements out about 20' or so are
>> secure. Dealing with the DXE tubing when <it gets down below 1" or so I
>> don't want anything too heavy. Also don't want to drill and weaken the
>> dipole. I actually came up with some 'rings' from Wilco just about the
>> right size that would slip over the 0.5", 0.625", 0.750" to I believe the
>> 0.875". There I <could use 1/2"-1 1/4" hose clamps to make sure the ring
>> doesn't slip further up. Just the dacron wrapped around the ring might be
>> enough to keep that from happening but I don't trust it.
>>
>>
>> <I'm not sure I could trust just using the hose clamps to hold the dacron
>> line but I don't want to drill and weaken the tubing in any way.
>>
>>
>> <Any better idea? You can see a few pictures of what I'm building on my
>> QRZ/KI7M page.
>>
>>
>> <Terry
>>
>> <KI7M
>>
>> ## Ken, W3JK, uses a 2 piece machined aluminum clamp, thick,
>> rectangular, that goes around the tubing in question.
>> On the top part of the clamp, a piece of 1 x 1 x .125 angle aluminum
>> is bolted, using the same pair of ss bolts as the
>> 2 x piece clamp. The vertical part of the angle al is where the truss
>> terminates... with just a hole in the vert portion of the
>> angle al. Use a small thimble etc, so the dacron does not bear down on
>> the edges of the hole. Ken will make a couple of pairs
>> for you, if he knows the exact tubing OD in question. Then they wont
>> slip.
>>
>> ## I looked at your pix. I would use better mast to rectangular plate
>> clamps.... vs the muffler style clamps you show in the pix.
>> Use a pair of the dx eng style muffler clamps.. the ones that have the
>> SOLID al saddle, then they have loads of surface area. The SS
>> u bolts that come with them are extra long threads, that will handle any
>> thickness al plate. You also
>> need a solid fiberglass center insulator. Without it, you have way too
>> much stress right in the middle.
>>
>> ## heres the real concern. Did you run the design through something
>> like the DX eng yagi mech software program ???
>> 66 ft long and starting with just 1.25..and down to the typ .375
>> even with thick, inboard sections, is going to have a tough
>> time with high winds... esp with dipole broadside to the wind. If we
>> knew the exact tubing schedule used, which means exposed
>> tubing lengths and also overlaps, and wall thickness, or if any inner
>> liners used etc, etc, then it can all be run through the dx eng mech
>> software very quickly.
>>
>> ## Your pair of over head truss lines wont buy you anything for
>> increased wind speed, only sag, and sag from snow and ice loading.
>> You also require horizontal dacron truss lines to handle increased wind
>> speeds. Horz truss lines will also minimize horizontal
>> deflection for XXX wind speed. If the ele deflects too much, then
>> you also get this effect called... wind induced swr.
>>
>> ## The dx eng yagi mech program will spit out how much vertical..and
>> horz deflection you will get..and also factor in both vert
>> and horz truss lines.
>>
>> ## At 1st glance, I just cant see your 66 ft long ele
>> surviving...when its only 1.25 inch OD in the middle. 1.25 is what you
>> would typ
>> use for the center of a 20m ele. For a 66 ft long dipole, 2.00 inch is
>> typ used..then tapering down to .375 at the tips. Even then, the inboard
>> 15 ft on either side of mast is typ heavy walled material, like .125.
>> And thats just to get it to survive a 85-90 mph gust. Without a horz
>> truss,
>> the ele deflection is insane with high winds. Typ a single horz truss
>> is used, and terminates 15 ft from the mast.
>>
>> Jim VE7RF
>>
>> _______________________________________________
>>
>>
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>
>
>
> --
> - 73 -
> - Joe W6JWP
>
--
- 73 -
- Joe W6JWP
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