[TowerTalk] [Bulk] Re: 90 degree coax bend atop a crankup tower

[Patrick Greenlee]

Thanks grant.  Apparently I was set to worrying over a non problem. I 
have seen but not used the Chinese finger cuff things for pulling wires 
through conduit using a winch and 3/4 inch rope.  I hadn't seen the 
lace-on variety but those sound really handy.

Thanks again, a little experience trumps a whole lot of speculation.

Patrick   NJ5G

On 6/5/2015 9:39 AM, Grant Saviers wrote:
> Tis the simple answer.  Use a Kellems grip and then there is no stress 
> on the bend.  They are available to slide over the end of the cable or 
> as "lace on" so they can go on an established length or where a 
> connector on the cable is larger than the expanded diameter.   LMR400, 
> Buryflex, LMR600UF and the like have a specified tensile strength of 
> 350 to 400# and a weight per foot of 0.07 to .16#/ft so one grip at 
> the top handles up to 110' crank up with better than a 2:1 safety factor.
>
> Grant KZ1W
>
> On 6/5/2015 4:32 AM, ve4xt at mymts.net wrote:
>> Wouldn't holding the coax with a sling-type grip in such a way that 
>> the bend itself is a tension-free loop, solve both problems?
>>
>> The issue in both cases is the unsupported weight of the coax pulling 
>> on the bend, yes? So if you took all the weight off the bend...
>>
>> Or am I missing something?
>>
>> 73, Kelly
>> ve4xt
>>
>>
>> Sent from my iPad
>>
>>> On Jun 5, 2015, at 12:15 AM, "Roger (K8RI) on TT" 
>>> <K8RI-on-TowerTalk at tm.net> wrote:
>>>
>>> Coax has two bend radius listed. A repeatable radius and a one time 
>>> bend.  It's a good idea to stay well away from both of these.  The 
>>> one time bend can be a very short radius. Short enough that the 
>>> center conductor will want to migrate off center given enough time 
>>> just laying on a flat surface.  The repeatable bend radius is 
>>> usually quite a bit larger and "should not damage the coax over a 
>>> given number of bends. No, I don't know the number, but the minimum 
>>> repeatable bend radius can still stress the coax.
>>>
>>> Now hang a load on the coax in a vertical run.  The center conductor 
>>> will tend to migrate downward.  In a 100 ft vertical run it's often 
>>> enough for N type connectors to lose continuity.   If the coax is 
>>> supported only from the top with a relatively sharp bend, the center 
>>> conductor will migrate off center.  That's why several small loops 
>>> evenly spaced up the side of the tower will remove the load from 
>>> that top support.
>>>
>>> There are several methods of supporting the coax from the top on 
>>> crank up towers.   Wire mesh and rope slings do a good job of 
>>> holding the coax, but do nothing for the linear migration of the 
>>> center conductor.  Several commercial ones linked to on here appear 
>>> to do a pretty good job,
>>>
>>> Too sharp a bend causes the off center migration, while too wide a 
>>> bend will allow the linear migration.  There has to be "a best 
>>> radius" for each size and type of coax.  I'd choose about twice the 
>>> repeatable bend radius.  No concrete proof, it just looks right. Not 
>>> exactly a scientific approach.
>>>
>>> Tall, crank up towers put a lot of stress on the coax supported only 
>>> from the top.  Unfortunately supporting the coax at intermediate 
>>> heights brings a whole new can of worms.
>>>
>>> 73
>>>
>>> Roger  (K8RI)
>>>
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