[Top] [All Lists]

Re: [TowerTalk] Tower Coax Support Sleeve

Subject: Re: [TowerTalk] Tower Coax Support Sleeve
From: <>
Date: Tue, 20 Mar 2007 20:54:12 -0400 (EDT)
List-post: <>
Lets not forget ice loads!  Most of the land mass of the United States
is subject to icing.  Many areas -- including my apparently benign 
location in central Maryland -- can and does accumulate 3/4 inch radial
ice loads.

Wind will also damage coaxial cables if it causes it to rub on any


---- Original message ----
>Date: Tue, 20 Mar 2007 19:15:00 -0500
>From: Red <>  
>Subject: Re: [TowerTalk] Tower Coax Support Sleeve  
>To: Jim Lux <>, TowerTalk <>
>Many thanks, Jim;
>Your calculations and experience appear quite conclusive.  We don't need 
>to worry too much about the weight of common coax overloading the 
>tensile strength when it is supported at a single point, but we need to 
>prevent the increased tensile load due to wind from exceeding its 
>strength by tying it to a structure to support the horizontal load.  
>That may require a clever solution on telescoping structures.  It's been 
>many years since I used a telescoping tower.  If I remember correctly 
>(and I'm not sure of that!), I suspended the coax inside the sections 
>and carefully handled it to make sure it wasn't damaged while lowering 
>or raising or lowering the tower.  I'm sure that coax was subject to 
>flapping in the wind, within the confines of the tower.  I used it for 
>only a couple years before replacing it with a freestanding tower with 
>all coax and control cables secured to a tower leg at short intervals to 
>prevent flapping.
>73 de Red
>Jim Lux wrote:
>> So, 100 ft of RG213 will weigh 11 lbs, which is a lot less than the 
>> breaking strength of 160 lbs. Granted, you probably want to stay away 
>> from the absolute limit.
>> Wind loads might well be a bigger problem.  A 1/2" diameter pipe 100 
>> ft long could have quite a bit of wind drag.  In fact, this is the 
>> real limiter, I think.  A quick back of the envelope shows that the 
>> wind load on a 1/2" diameter tube at 80 mi/hr is about 0.7 lb/ft.  The 
>> analysis goes just like a catenary except the wind load is used 
>> instead of gravity.  Say you've got a 100 ft run, and you allow it to 
>> move a foot (like sagging 1ft in a 100ft span).. The tension in the 
>> coax would be 870 lb.  If you allow 2 meters (6 ft) of displacement, 
>> the load goes down to about 70lbs, still high. And, in that situation, 
>> the cable would probably flap around.
>> Moral of the story.. the weight of the cable isn't a big deal, wind 
>> loads on the coax is. So you need a fairly reasonable grip to hold it 
>> at top, but you need to tie the cable to the tower to take the lateral 
>> loads.
>> And, now actually having run some numbers, it seems to match practical 
>> experience at field day.  The disasters with coax are almost always 
>> wind induced.
>> Jim, W6RMK

TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>