[TowerTalk] re beam antenna truss

[K8RI]

On 12/25/2012 2:47 AM, Jim Thomson wrote:
> Date: Mon, 24 Dec 2012 12:30:26 -0500 (EST)
> From: jcjacobsen at q.com
> To: w1dxh at aol.com
> Cc: towertalk at contesting.com
> Subject: [TowerTalk] re beam antenna truss
>
> Yo,
>
> Steve is looking for ideas on how best to "truss" a boom.
>
> I'm amazed that no one has also suggested that no matter what he ends up using, he should make sure to use thimbles to protect the wire/rope/philly where it goes thru the eye bolts.
>
>
> 73
> K9WN Jake
>
> ## Putting a SS eye bolt through a thin wall boom is asking for trouble.  However it will work on a thick wall boom.  What else that works good is to use those wrap around,
> cast aluminum irrigation clamps, they are at least .187” thick.  Then replace the lag bolt with a SS one.. and nylock nut..+ thimble!


I agree with all but the Nylock nut unless the insert is protected from 
nature.  I've had the the inserts completely disintegrated in less than 
a year. If you use them, paint over with something to protect them.

73  Roger  (K8RI)


  Underneath the rounded head is a square... and this square
> fits like a glove into the mating square hole in the cast AL clamp.  You can get em cheap at any irrigation supply place.   But I have only seen them in 2”-3”-4”.
>
> ##  leesons method of using a 3 point truss was also mentioned.  KLM used the same trick on it’s 58’ long 20m boom’s years ago.   The trick is the outriggers + mast are all
> 120 deg apart.  If not there is no uplift support.
>
> ##  yet another method is to use say a 4’  wide cross bar mounted to the mast, well above the boom, then use 2 x truss lines on each side of mast,, converging to a  common
> point, towards the ends of each side of the boom.  Although this looks good, and was used all the time in the 70’s.... fact is, it provides zero side support.
>
> ## another variation of above is to use a short cross bar on the ends of the boom...and again, use 2 x truss lines... but this time they converge to a common point on the mast...
> again, that scheme provides very little side support.
>
> ## IMO, build the boom such that it does not require side support, only vertical support.
>
> ###  On a really long boom,say a 60’ boom, you can run a truss line out on each side of the mast, and terminate aprx 15’  on either side of the mast.   Then run a 2nd pair of truss lines
> from the mast.... but terminate the 2nd pair at the extreme ends of the boom, or close to the ends..... sorta like using 2 sets of guy wires on a tower instead of one set.
>
> ##  You will also put way less stress on everything if the truss line terminates on the mast, well above the boom.  5/32” galvanized winch cable works great as a truss line...as does
> 5/32” SS.  I use nicropress crimps at the boom end, and also the mast end.  Then a small turnbuckle at mast end to tweak the tension.  Use thimbles at all ends.
>
> ##  I’m getting too old for this long boom stuff these days.  36’ is as long as I have on all my yagi’s....including 40-20-15m.  The difference in gain is so miniscule it’s really not worth the effort.
> I can more than make up the difference  with a bigger amp, lower loss coax, or greater height.  A pair of shorter length boom yagi’s, stacked, will usually do as well, or better, than a single
> long boom monster, way up high.
>
> Later........... Jim   VE7RF
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