[TowerTalk] beam antenna truss

[Grant Saviers]

Dave Leeson W6NL, in "Physical Design of Yagi Antennas" (check Amazon) 
advises that trusses should resist sway in two planes - horizontal and 
vertical.  Wind up/down drafts can cause as many problems as side on 
force.  Particularly since hams like to place antennas on top of hills. 
So to really stabilize for wind loads a minimum of three guys are 
needed.  Two above or below the boom on outriggers perpendicular to the 
boom and one on the opposite side of the boom to the mast.

Of course, if you have enough wind strength and are only reducing the 
boom weight stress, only one truss is needed.  For booms that is 
possible, but it is unlikely for elements - wind loads usually are 
significantly higher the the weight load.  If your site has significant 
icing, it is potentially another big weight load to manage.

Another piece of advice from him was to guy long elements at 6 to 12" 
each side of the boom to reduce the element swaying motion on the 
boom.   These could be integrated into a three truss boom support, two 
upward to a crossbar on the mast above the boom and one down to the 
mast.  I think Phillystran is the best choice for all of these.

Grant KZ1W


On 12/23/2012 6:22 PM, K8RI wrote:
> On 12/23/2012 8:30 PM, Patrick Greenlee wrote:
>> Don't use nylon as it is too stretchy. Don't use polypropylene as it
>> lacks UV resistance (Good water ski rope though) Dacron is a good very
>> low stretch rope, preferably treated for UV resistance but you can put a
>> sleeve over it like cut from a throwaway garden hose .  You can cover
>> the knots with black silicone caulk and prevent the knots from
>> weathering.  Phillystran is an excellent material but...don't clamp it
>> or tie it in a knot.  Use the approved methods of terminating it: 1. the
>> Chinese finger grabber type grips or the 2. the two part catalyzed
>> potting system. Not really practical to use the grips on a really short
>> piece of Phillystran.  some argue against a conductive material but
>> commercial antennas use conductive material often. If you have the
>> ability to do the math or perform the tests you can find out what the
>> effect of a conductive material is.
>
> For a relatively light weight boom I'd not hesitate to use clamps, but 
> remember you will lose about 50% of the rated strength.  I use 3 
> clamps  and a minimum torque, or clamping force for the small 
> Phillystran.  I would prefer the potted ends when using larger cable 
> and heavier booms.  OTOH with long booms and lower frequencies the 
> "Big Grip" ends should not create a problem. Multiple trusses for the 
> long boom.  I don't think they would be a problem on 20, but won't 
> offer a guarantee.  <:-))
>
> 73
>
> Roger (K8RI)
>
>
>>
>> 73 Patrick AF5CK
>>
>>
>> -----Original Message----- From: Cqtestk4xs at aol.com
>> Sent: Sunday, December 23, 2012 7:10 PM
>> To: TOWERTALK at contesting.com
>> Subject: Re: [TowerTalk] beam antenna truss
>>
>>
>> The cheapest is to use is wire.  However, this can cause interaction
>> accord
>> ing to some, with the Yagi.
>>
>> Many use rope.  On my M2 antennas Dacron is used, fastened to the 
>> boom  by
>> mean of an eyebolt through the boom.
>>
>> Some guys use Phillystran in the same fashion.
>>
>> Bill KH7XS/K4XS
>>
>> In a message dated 12/24/2012 12:50:36 A.M. Coordinated Universal Ti,
>> w1dxh at aol.com writes:
>>
>>
>> Looking for info on best way to truss a long boom yagi. What is the best
>> material to use? How to secure to boom etc. Thanks for  help.
>>
>> 73,
>> Steve  W1DXH
>> _______________________________________________
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